Lighting Installation - Basic vocational knowledge (Institut f�r Berufliche Entwicklung, 164 p.)

Lighting Installation - Basic vocational knowledge (Institut f�r Berufliche Entwicklung, 164 p.) 2. Elements 2.1. Basic Terms in Lighting Engineering 2.2. The Eye and its Visual Capacity 2.3. Colour, Light and Space 2.4. Quality Characteristics of Lighting 2.4.1. Indoor Lighting 2.4.2. Outdoor Lighting

Lighting Installation - Basic vocational knowledge (Institut f�r Berufliche Entwicklung, 164 p.)

2. Elements

2.1. Basic Terms in Lighting Engineering

Radiation - general

Emission or transmission of energy in the form of electromagnetic waves or corpuscles.

These electromagnetic waves or corpuscles themselves.

The wavelength of this radiation is unlimited.

Radiation - visible

Radiation causing visual sensation immediately and directly. The visible radiation comprises the energy in the wave bands between 380 and 780 nm.

Light

Characteristic of all perceptions and sensation the visual organ is capable of mediating.

Radiation suitable for exciting the visual organ.

Relative luminosity factor

The ratio of the radiant flux with the wavelength Lambda (m) and the radiant flux with the wavelength Lambda both radiations causing the same brightness impression in certain photometrical conditions.

Lambda (m) has to be selected in such a way that the maximum of this ratio is equal to 1.

The graphic representation of this ratio shows the spectral photopic eye response curve for daylight and night vision (Fig. 1). For the purpose of phototechnical evaluation of all physical values these must be related to the mentioned curve.

Therefore, the phototechnical formula symbols get the index ‘v’, whereas the physical values bear the index ‘e’ for ‘energy’.

Figure 1. Spectral-response function of the eye depending on the wavelength

1 for cone vision (day vision)
2 for rod vision (night vision)

Luminous flux

Value derived from the luminous flux in such way that the radiation is assessed according to its effect on a selective receiver the spectral sensitiveness of which is given by the standardized degree of brightness.

Unit lumen (lm)

Lumen is the internationally agreed unit of the luminous flux.

The luminous flux characterizes the light power.

Light efficiency

Quotient out of the luminous flux and the wattage applied.

Unit lumen per watt

Light intensity

Quotient out of a luminous flux emitted by a light source into a solid angle element around the considered direction and this solid angle element.

Figure 2. Representation of light intensity

1 light source, 2 direction of view, 3 solid angle, 4 portion of the luminous flux which is registered from the direction of view

For calculating the illumination it is important to know in what direction the lighting fitting distributes the luminous flux.

That is to say one must know the spatial distribution of the luminous intensity of the illuminator. For this, the luminous intensity is represented as a radius vector in a polar diagram.

All the vectors start from the same point - pole -; their respective length is proportional to the values of the luminous intensity in the various directions. By meridian sections one gets the light distribution curve (LVK) in these planes.

Figure 3. Basic representation of the light distribution curve

1 light intensity in candela

With the representation of the solid of light distribution by light distribution curves with many lighting fittings one cannot manage with one sectional axis; it is necessary to determine plane systems. Three plane systems are preferred.

- Planes the lines of intersection of which stand on one supposed illuminator axis and lie in a horizontal plane through this axis.

The planes a re called A-planes, the angle of swing of the planes is represented by beta.

Figure 4. Light distribution curve (A plane)

1 illuminator axis
2 rotation axis
3 beta = 40 degrees
4 beta = 20 degrees
5 beta = 0 degrees
6 light distribution curve in the A plane

- Planes the lines of intersection of which coincide with the supposed illuminator axis. These planes are called B-planes, the angle of swing is marked by alpha. The alpha- and beta-angles are counted from 0 to +- 180 degrees. The direction of a luminous intensity I in the A-planes system is clearly defined by the value A (beta, alpha), which is equivalent to beta = 40 degree and alpha = 30 degrees. The direction of a luminous intensity I in the B-planes system is clearly defined by the indication of B (alpha, beta), which is - in this example - alpha = 30 degrees and beta = 40 degrees.

Figure 5. Light distribution curve (B plane)

1 illuminator and rotation axis, 2 alpha = 40 degrees, 3 alpha = 20 degrees, 4 alpha = 0 degrees, 5 light distribution curve in the B plane.

- Planes the lines of intersection of which stand vertically on the illuminated surface and which pass through the centre of the illuminator.

These planes are called C-planes; the angle of swing is called gamma and counts from 0 to 360 degrees - semiplanes.

Figure 6. Book-leaf representation of a low-frequency illuminator in the A plane

1 (candela divided by 1000 lumen), 2 measuring plane, 3 beta = 0 degrees, 4 beta = 50 degrees.

Figure 7. Channel flood lantern with light distribution curve

Close-radiant with an illuminator efficiency of 0.74

1, 2 radiation planes

Wide beam with an iliuminator efficiency of 0.72

Luminance

Luminance - in one direction, at one point of a radiating or irradiated surface, or at a point of an optical path.

Quotient of the luminous flux leaving a surface element enclosing the respective point, hitting the surface element or penetrating it and spreading within a solid angle element in a given direction and of the product of the transilluminated solid angle element and the surface element on one plane vertically to the direction of the radiation.

Figure 8. Representation of luminance

1 light intensity for epsilon, 2 transilluminated solid angle element (surface element), 3 vertical orthogonal projection of the surface element

Unit of candela per square metre

Illumination

Quotient of the luminous flux received by a surface element which contains the point considered and of the surface of this element.

Unit of lux (lx)

Illumination is that value in lighting engineering which is mainly used as the basis of projecting indoor and outdoor lighting installations, except street lighting installations.

In this context it is mostly necessary to picture to oneself the distribution of illumination. In many cases, the indication of the average illumination is sufficient. In this case, the surface the average illumination is related to must be accurately marked off.

For characterizing the local evenness it is required to know the maximum and minimum illumination on the calculated surface with outdoor installations. Often it is also important to know the evenness on a number of vertical planes and to find out the minimum and average values of certain vertical planes. After having measured or calculated the illumination in a number of points of one plane, the values in these points can be projected vertically as vectors on the surface (measuring plane); the values are given by the length of the vectors. The enveloping surface of these vectors is the illumination shape that gives a picture of the distribution of illumination on the measuring plane.

By connecting the points of the same illumination within this shape the representation becomes more illustrative - isolux surfaces.

Figure 9. Illumination figure of a lighting fitting fixed to a lamp pole by a holding fixture, useful height = 9 m

1 illumination in lx, 2 width of the measuring plane in m, 3 length of the measuring plane in m

In practice, sections in different planes of the shape are sufficient. The vertical section produces the rectangular illumination diagram.

Table 1. Survey of the basic values, their symbols, units and relations in lighting engineering

Table 2. Luminance in various systems of units

Table 3. Illumination or illuminance in various systems of units

In addition to the mentioned basic units distinguishing marks - materials indices - are required, which mainly characterize the building materials in lighting engineering. These include materials for lamps and lighting fittings and all materials influencing the illumination and entire impression of a room and which exert an influence especially on the mood of the people staying in this room, e.g. machines, surfaces of the room, work clothes, etc.

The qualities of a material relevant for illumination engineering are expressed and represented by:

Reflection, transmission and absorption

This is the throwing back or passing through of a radiation by or through a surface or medium without any change of frequency within the monochromatic portion of the radiation and transformation of radiant energy into another form of energy by interaction of light with matter. There are different types of reflection and transmission:

Specular reflection

Reflection without scattering according to the rules of optical reflection such that all reflected rays have the same direction.

Figure 10. Directed reflection, transmission

Diffuse reflection

The reflection of rays from a surface such that the reflected rays have various directions, as far as the rules of optical reflection do not become noticeable macroscopically.

Figure 11. Diffuse reflection, transmission

Mixed reflection

Simultaneous specular and diffuse reflection.

Figure 12. Mixed reflection, transmission

Perfectly diffuse reflection

Diffuse reflection such that the reflected radiation is evenly distributed in all its directions as to radiant intensity and luminance per unit area - Lambertian light source.

To the types of transmission the respective definitions apply.

Among the mixed reflections also counts the term of Gloss (of a surface)

Quality of a surface such that - by specular reflection or an acute reflection indicatrix - it shows bright reflected lights or the reflected pictures of bright things.

Gloss can essentially support the recognition of a form, but it may as well impede the recognition of details.

Therefore, this phenomenon must be paid special attention to when a lighting installation shall be constructed.

Table 4. Characteristics of illuminating engineering materials - glass -

Table 5. Characteristics of illuminating engineering materials - metals -

Table 6. Characteristics of illuminating engineering materials - paper and paint coats -

Table 7. Characteristics of illuminating engineering materials - various building materials -

2.2. The Eye and its Visual Capacity

The image of the environment is perceived and its physiological and psychological processing and assessment for experience of life is effected by the

Visual organ

It is the entirety of eye, optic nerve and cerebral cells that transforms the light stimulus into those nerve excitations which are the subjective correlate of the visual perceptions.

At first, the external light stimulus hits the eye.

Eye

This is the part of the visual organ which perceives the image of the external world and which transforms this image into nerve excitation.

Figure 13. Horizontal section through the human eye

1 cornea (transparent), 2 crystalline lens of the eye, 3 anterior eye chamber, 4 iris, 5 ciliary body, 6 sclerotic coat, 8 retina, 9 vitreous humour, 10 fovea centralis, 11 optic papilla, 12 optic nerve

The most important part of the eye is the retina.

Retina

The light-sensitive membrane of the eye consisting of the light receptors - cones and rods - and nerve cells. The latter lead the excitation to the optic nerves. Cones and rods are embedded in the retina.

Cones

Especially light-sensitive elements of the retina which presumably enable light and colour vision of the light-adapted eye - day vision.

Rods

Especially light-sensitive elements of the retina which most probably enable vision by the darkness-adapted eye.

The rods are not likely to contribute to colour vision. (Night vision). The distribution of cones and rods on the retina is different.

In the region of the breakthrough of the visual nerve and the choroid through the cornea there are neither cones nor rods.

For this reason, this part of the eye is called the “blind spot”. On the level of the optical axis of the eye there is a concentration of rods. Here is the region of sharp vision. This part of the retina is called fovea centralis.

Fovea centralis

Thinned and therefore concave central part of the yellow spot showing almost only cones. Region of accurate vision. It is corresponding to a visual angle from 0.017 to 0.035 rad (1 to 2 degrees) in diameter.

From this part of the retina towards its periphery the portion of rods in the retina grows continuously. Finally, there are only isolated cones in the periphery of the retina.

With the help of these cones and rods, which have a very differentiated sensitiveness to light, man is able to orient himself in bright sunshine and in moonlight as well. However, experience has shown that the adaptation, especially to a dark environment, takes a certain time. The ability of the human visual organ to adapt itself to light is called

Adaptation

The process of the visual organ adapting itself to luminances and chromatic stimuli in the range of vision. Condition achieved after completion of the process. The term ‘light adaptation’ is used if the luminance is at least a few candela per square metre; if it is less than some hundredth parts of a candela per square metre one speaks of ‘dark adaptation’.

With a physical radiation in the range from 380 to 780 mm seeing is enabled by the cones and rods.

Seeing; visual perception - specific excitation of the sensory system of the eye.

Recognition of the surrounding world by sensory impressions caused by incident radiation.

In this process, rods and cones are included separately or in common because they absorb the incident radiation. The electric pulses created during the absorption of the radiation are led to the brain via the optic nerve, which is the junction of the ends of cones and rods, and - in the optic centre - result in conscious perception.

Perception

Complex content of the consciousness resulting from sensorial impression and contents of the memory (shape).

Especially, the visual perceptions drop in the ideas we form of the existence, form and position of external things.

Since, with the process of seeing, it is not as often a question of stationary things as it is a question of objects in motion, the time for which these objects come into vision is of special importance. The movement of the things, that is to say the impression of movement, may also be caused by the movement of the eyes. Thus, the speed of perception must be considered as a decisive value in the process of seeing.

Speed of perception

Reciprocal of the interval of time passing between the moment of objective exposure of a thing to the eye and the subjective perception of the image.

This term is equivalent to that of ‘speed of perception of form’. Another parameter in the context of the perception of the environment is colour.

Colour

- Colour sensation: That characteristic of a visual sensation which makes it possible to distinguish between two neighboring parts of the viewing field equal as to their size, shape and structure but different in their spectral condition.

- Colour valence: Characteristic of a visible radiation which makes it possible to distinguish between to neighboring parts of the viewing field equal as to their size, shape and structure but different because of the different spectral condition of the respective radiations.

Colour sensation is only possible if object, physical radiation and action of the eye concur. Colour sensation can be influenced by the colour of the object as well as by the spectral composition of the radiation. In general, the colour of the object is called body colour.

Body colour

Colour of a non-luminous object: colour sensation caused by a non-luminous object.

The CIE definition of the term of ‘seeing’ speaks of the ‘recognition’ of differences in the surrounding world. This can be put in more concrete terms: The eye distinguishes on the one hand brightness and luminance contrasts and on the other hand colour contrasts.

Contrast

- Subjectively: Mutual influencing of two immediately neighboring or successive visual impressions - simultaneous contrast, successive contrast.

- Objectively: The size of the luminance contrast defined by formulae.

If the visual function is reduced by an unfavourable distribution of luminance, too high luminance or too great spatial or temporal luminance contrasts causing an unpleasant feeling - discrimination threshold, etc. - we speak of dazzle.

Literature distinguished between two main types of dazzle:

Psychological dazzle

Kind of dazzle causing an unpleasant sensation without a distinct reduction of the visual capacity being necessarily linked with this feeling.

Table 8. Glare terms according to Schober

Physiological dazzle

Kind of dazzle leading to a reduction of the visual capacity without necessarily causing an unpleasant sensation simultaneously.

With moving objects, flicker may cause a special effect:

Stroboscopic effect

Illusion of motion consisting in the fact that objects in motion appear as resting or in a condition other than their real one because they are illuminated by periodically variable light of a suitable frequency.

2.3. Colour, Light and Space

The aims of illumination include the following components:

Light (light source, lighting fitting), colour (colours of the ceiling, walls and furniture etc.) as well as the spatial conditions (dimensions of the room, measuring planes). These have to be considered in order to achieve an economical illumination.

The efficiency of the lighting installation is determined by the possibility of directing the light of the respective light source, to diffuse it - according to purpose - or to reflect it.

A distinction is made between illuminator efficiency and degree of the effect of depth. Both together result in the efficiency of illumination.

Efficiency of the illuminator

The illuminators shall fulfill their task of directing the luminous flux with the lowest possible light flux loss. Light flux losses are caused by losses in transmission and reflection at lighting fitting components. The efficiency of an illuminator (optical efficiency) is the ratio of the light flux emitted by the illuminator Phi (2) and the sum of the light flux generated by the individual lamps within the respective illuminator Phi (1).

Degree of the effect of depth

For projecting indoor lighting installations according to the light flux method, the degree of the effect of depth Eta (R) has to be determined. It considers the effects of the room on the direction of the light flux on the plane of calculation Phi (3). It depends on the proportions of the room, the values of the degree of reflection of the limiting surfaces of the room and the mode of construction and is defined by

Degree of illumination efficiency

The degree of the illumination efficiency Eta (B) is calculated from the degree of efficiency of the illuminator Eta (L) and the degree of the effect of depth Eta (R):

Eta(B) = Eta(L) x Eta(R).

Thus, the degree of illumination efficiency is the ratio of the light flux Phi(3) reaching the area of use and the lamp-emitted light flux Phi(1):

The degree of illumination efficiency has very wide limits; in practice values between 0.05 and 0.9 are to be found.

Light and colour

The use of colours in a working room deserves more and more attention because due to the ever more sophisticated processes of work the required illumination values at work places amount to 1000 lx and more. A consequence of the putting into practice of so great an illuminance is that the luminance in the range of vision can no more be an optimal one, if no coloured surfaces are used in the working room.

The spectral composition of the light energy emitted by the lamps is different depending on the kind of light generation - temperature radiators or gas-discharge light source - and on the type of lamp which is used.

In warm light colours also warm body colours make themselves felt in a pleasant way, whereas the low proportion of short-wave radiation of these light sources more or less “kills” cold colours such as bluish green, blue and purple. With neutral-white light sources, all colour shades are assessed as equal. Lamps of this group are called ‘safe light colours’.

As background colours - wall and ceiling colours - white or light colours of little intensity such as pastel colours are preferred. Here, one can speak of ‘safe wall colours’. On the other hand, very dark background colours are accepted, too. Colours of a medium intensity and brightness are estimated least.

The question whether or not the colour of an object is felt as pleasant or unpleasant mainly depends on the colour of the background before which the object is presented. Therefore, a well chosen background colour may counteract even a ‘bad light source’ as well as, the other way round, a disadvantageous background colour may spoil the effect of a ‘good light source’.

Independent of the light colour and the colour of the background, the cold colours blue, bluish green, green and purple are preferred as object colours. Therefore, they can be understood as ‘safe object colours’. On the scale of assessment they are followed by red, yellow ranks last.

Whereas for the background colours very little intensity is preferred, very intensive colours are suited best for the objects.

In general, women are inclined to choose warmer colours such as red, yellowish red, and yellow in contrast to men who give preference to the green and bluish green shades.

The colours of food, as a rule, look better in warm light than in colder light.

Two neighboring colours, generally, are felt as harmonious only if they are similar in their shades. The more the colour shades are distant from each other on the hue circle the less harmonious is the impression of the combination.

In spite of the above statements it must be said that the colours in a room create a satisfactory atmosphere only if they are lively and diversified.

Simple repetition of a design and of colours which have proved good, decorative and useful often leads to boredom, monotony and thus to the opposite of the desired effect.

2.4. Quality Characteristics of Lighting

2.4.1. Indoor Lighting

Decisive of the impression an illuminated room leaves is the distribution of brightness and colours in it, i.e. the ‘colour climate’ which by the CIE dictionary is defined as follows:

The colour climate is the physiologically existing and psychologically active atmosphere of a room resulting from light (illumination and its distribution, kind of illumination and light colour) and from colour (shade, degree of intensity, colour rendition and area distribution in a room) in connection with form.

The following criteria of assessment are applied to indoor lighting:

- physiological-optical assessment taking into consideration the visual work and thus physiological problems relating to work;

- psychological assessment concerning the agreeableness of lighting;

- hygienic assessment as to whether or not the light in its quality and quantity is healthy.

The quality characteristics of lighting are subdivided in four groups.

Table 9. Quality characteristics of illumination

Table 10. Assessing methods and criteria for determining the optimum illumination

Physiological investigations in the relations between illumination and working efficiency

Investigations have shown a direct connection between illumination and efficiency. It is to be seen that the efficiency increases depending on the illumination and the size of the detail of a visual task.

With an increasing fineness of the details, an intensified illumination leads to an increase in efficiency. In this context, of course the level of initial illumination must not be overlooked.

Since the physiological investigations in connection with efficiency are carried out over longer periods of time, conclusions can also be drawn with respect to fatigue and lighting as far as fatigue decreases with increasing illumination.

The investigations and findings in connection with the illumination intensity refer to an average visual capacity. The special conditions of seeing at an advanced age and the differences in individual visual capacity were very little considered. An immediate connection between visual capacity - especially visual acuity - and age has been proved. From the fact that younger people often have better eyes it cannot be concluded that older people are less efficient, because there are essential other factors to be considered such as vocational experience and the general attitude towards working. The losses in visual acuity that occur along with the advance in years of life can be balanced to a far extent by an increased illumination in the course of which the specific characteristics of the respective work must not be forgotten.

Glare and glare limitation

Visual capacity is reduced if there are too great differences in luminance within the field of view. In such case one speaks of glare or dazzle.

With indoor lighting fittings it is mostly a question of psychological glare. It causes a feeling of uncomfortableness in man.

The assessment of psychological glare and the limitation of it to a permissible degree is an important criterion of the quality of indoor lighting installations. It is distinguished between the glare caused directly by the illuminators in the room - direct glare - and the glare resulting from too great luminances in the field of view, from reflection and/or areas of great luminance within the range of working.

Figure 14. Radiation angle for glare evaluation

1 height difference between eye and illuminator, 2 critical range of the radiation angle, 3 distance of the last visible illuminator

2.4.2. Outdoor Lighting

Similar to indoor lighting, also here the quality depends essentially on the luminance and its distribution in the field of view. Some statements made on indoor lighting also hold good for outdoor lighting.

Not all factors influencing the quality of illumination can be expressed in terms of quantity yet. Therefore, it is important to understand the correlations of the influencing factors in their effect on the quality of lighting. The most important quality characteristics are:

- luminance
- evenness of luminance
- illumination and evenness of illumination
- glare limitation
- optical guidance and additional information
- light design
- operation.

Luminance

Luminance determines the impression of brightness and the visual perception of the range of work or the traffic area. Seeing is the “recognition of differences in the surrounding world...”.

This is a question of recognizing differences in luminance - brightness differences - and differences in colour. Differences in colour - colour contrasts - generally play a subordinated role in outdoor lighting, because in outdoor areas they are less often represented and - with a low level of illumination - they may be beyond the threshold of visibility at that.

With an increasing luminance, visibility increases, too. This is to say, the eye becomes more sensitive to differences. A further increase in the adaptation luminance of outdoor lighting causes an essential increase in the sensitiveness to differences. For the time being, the luminance of street lighting is approximately 1 candela per square metre. The visual angle can mostly not be influenced. The luminance of the surrounding field can be increased only by much expenditure. Therefore, the creation of favourable contrast conditions is an important task.

Questions for repetition and knowledge test

1. What is the meaning of the term of ‘light flux’?
2. What is understood by ‘illumination efficiency’?
3. By what factors is the quality of a lighting installation determined?

Lighting Installation - Basic vocational knowledge (Institut f�r Berufliche Entwicklung, 164 p.) 3. Calculation of Illuminance (introduction...) 3.1. Luminous Flux Method for Interior Space 3.2. Luminous Intensity Method - for Rotation-Symmetrical Lighting Fittings

Lighting Installation - Basic vocational knowledge (Institut f�r Berufliche Entwicklung, 164 p.)

3. Calculation of Illuminance

The illuminance required in a room or at a working place must be realized - according to the respective visual task - by a suitable number and type of lamps and lighting fittings and their arrangement. For this purpose it is to be calculated how many lighting fittings and lamps are necessary. This can be done by finding the required luminous flux first.

Through the luminous flux of the individual lighting fitting the required number of lighting fittings can be found out. This is called luminous flux method. It is also possible to proceed this way: Calculation from a given arrangement of illuminators and the given luminous flux per illuminator taking into consideration the light distribution of the illuminators the illuminance, for instance at a certain point of the working area. Here, one speaks of the luminous intensity method. Then, the lamp supply of each illuminator or the arrangement of the illuminators must be altered by the difference between the required and the calculated illuminance. It was refrained from an accuracy not required in practice in favour of a more facile application of many calculating methods. The accuracy of the calculated luminous flux or of the calculated illuminance is influenced by the tolerances of the individual calculation factors such as the luminous flux of the illuminator, illuminator efficiency, light distribution curve. Unfortunately, the tolerances of the most important value - the luminous flux of the illuminator - are within wide limits; with gas-discharge light sources the tolerance amounts to 10 or even 15 % of the nominal value. Another source of inaccuracy consists in the tolerances of the illuminator efficiency, mainly with the gas-discharge lamps, which in their efficiency depend on temperature. Here, the respective efficiency for a certain surrounding temperature must be indicated in connection with correction factors considering the different thermal behaviour of the illuminators and the illuminator equipment.

3.1. Luminous Flux Method for Interior Space

To calculate the required number of illuminators that shall be symmetrically distributed in a room the following details must be given:

1. The required medium illuminance depending on the visual task

Table 11. Minimum illumination

2. Colour of the ceiling and walls

Table 12. Reflection factors (selection)

3. Surface of the room (dimensions)
4. Suspension height of the illuminators
5. Measuring plane (height of floor)
6. Cleaning cycle, degree of getting dusty

Table 13. Depreciation factor with indoor lighting installations

7. Type of illumination

Table 14. Types of illumination

8. Type of light source

Table 15. Survey of light sources

The calculation of an interior space illumination shall be demonstrated by an example of the luminous flux method. The result is of sufficient accuracy.

A classroom shall be illuminated by fluorescent lamps. The double-lamp illuminators are evenly distributed in the room. The room is 7.00 m wide and 12.00 m long. The illuminators shall be suspended at a height of 2.60 m. The measuring plane is supposed to be 0.75 m (level of the desks). The degree of contamination is normal. The ceiling is chalk-white, the walls have an ochre painting. Illumination is direct, the illuminators are not screened on their lower ends but have reflectors on top. The degree of efficiency is supposed to be 1.

Solution: Parameters

Solution: Calculating steps

1. Surface of the room

A = L x B = 12m x 7m =84.00 square metres

2. Useful height

hN = hA - ME = 2.60 m - 0.75 m = 1.85 m

3. Room factor

K = 4.3

4. Determination of the illumination efficiency with the help of Table 16: Basis is the rubric ‘direct’. Under the term of ceiling reflection 70 % (the nearest to 80 %), that column is chosen which comes next to the wall reflection, i.e. 50 %. This column is gone down until the value of K = 4 is reached.

Here, the value 0.45 (45 %) is to be found. This is the degree of room efficiency. Since the efficiency degree of the illuminator was supposed to be 1, it appears that the illumination efficiency is equal to the degree of room efficiency (0.45).

5. Determination of the total luminous flux

PHIges approximately 58,340 lm

6. Calculation of the number of lamps

7. Illuminator arrangement

The result is that double-lamp illuminators have to be evenly distributed in the room.

Hints concerning the selection of the lamps:

According to the principle of assigning lamps of a certain light colour to the individual activities, it has to be decided about the colour of light after having calculated the number of lamps required.

There are the following colour shades: white, warm-tone, warm-tone extra or white, warm-white, warm-white de luxe as well as universal-white, white de luxe and daylight.

In any case it is advisable - due to the variety of international manufacturers - to use the respective colour temperature for selection, (e.g. warm-white 2900 K; white 4300 K). Furthermore, the starting behaviour of the lamps should be considered. In a cool ambient temperature, fluorescent lamps of the standard type start very bad. In such case, cold-proof lamps should be used.

As has been stated, the calculation according to the luminous flux method includes the reflection capacity of ceiling and walls in the design of the lighting installation. No daylight support is added! It is also supposed that the colour of the ceiling and the walls remains unchanged, because otherwise the initial parameters of the illumination would change.

3.2. Luminous Intensity Method - for Rotation-Symmetrical Lighting Fittings

By this method, the illuminance on a surface to be illuminated is calculated, with direct irradiation by the light source and without consideration of reflecting surrounding surfaces (spotlight effect). With the illuminance given the light source can be found.

The following details are required for the calculation:

1. Average illuminance required for the visual task.

2. Type of illuminator with the appertaining light distribution curve indicated by the manufacturer.

3. Suspension height

4. Measuring plane

5. Degree of getting dusty

6. Type of light source

7. Angle of irradiation (indirect by lengths of reference)

Figure 15. Light distribution curve (rotational symmetrical representation)

1 light intensity in cd

Example of a calculation task concerning a lighting installation for an assembly surface (open-air surface). The result is of sufficient accuracy.

An assembly surface shall be illuminated by downlighters equipped with high-pressure mercury vapour lamps. Rough work - locksmith’s work - shall be carried out. The dimensions of the surface are 10 x 10 m. The downlighters shall be installed at a height of 4 m. The required lamp performance has to be found out, if 4 illuminators shall be used.

Angle of irradiation: This has to be calculated with the help of Pythagoras and function of angles according to the space dimensions, (acc. to Fig. 16). It amounts to approximately 41.2 degrees.

Figure 16. Dimensional sketch

1, 2, 3, 4, 6 suspension and/or mounting frames of the lighting fittings, 5, 6, 7 lighting points resulting from the angle of arrival alpha, 8 (2.5 m), 9 (10.0 m), 10 (4.0 m), primed 1 and 3 vertical rotation point below the lighting fitting.

Solution: Steps of calculation

1. To 41.2 degrees the corresponding cosine has to be determined. It is approximately 0.425.

2. From the light distribution curve, Fig. 16, approximately 350 cd (candelas) appear.

Application: At 41.2 degree, the curve is intersected.

From the point of intersection, the value is read radially on the vertical axis.

3. In order to be able to calculate the required luminous flux, the two formulae for Ep and la must be linked. If the respective values are put in as follows

Luminous flux of lamps in lumen (lm)
Illuminance in point ‘P’ in lux (lx)
Useful height in square metres
Light intensity from the light distribution curve in candela (cd)
Solid angle ratio for rotation-symmetrical light distribution
Depreciation factor (degree of getting dusty in %)

the result is a luminous flux of the lamps of 17930 lm

4. Determination of lamps

Selection:

High-pressure mercury vapour lamp 400 W = 23.000 lm
High-pressure sodium vapour lamp 250 W = 25.000 lm

5. Counter calculation:

Since the rated luminous flux is greater than the calculated one, it derives for the illuminance in point ‘P’:

for high-pressure mercury vapour illumination 128 lx
and for high-pressure sodium vapour illumination 139 lx

6. The illuminance adds in the middle of the working surface to 4 x Ep = 512 and 556 lx, respectively.

7. Directly under the illuminator the following illuminance is calculated:

Ep approx. 302 lx

With high-pressure sodium vapour lamps it would be

Ep approx. 328 lx

The illumination distribution, for instance with high-pressure sodium vapour lamps, would be as follows:

Questions for repetition and knowledge test

1. By what methods a lighting installation can be calculated?

2. What importance does the type of illumination have for the determination of the number of lamps?

3. What is the importance of the light distribution curve?

4. What is understood by the term of ‘illuminance shape’?

Lighting Installation - Basic vocational knowledge (Institut f�r Berufliche Entwicklung, 164 p.) 4. Measurements at Lighting Installations 4.1. General Remarks 4.2. Illuminance Measuring 4.3. Luminous Density Measuring

Lighting Installation - Basic vocational knowledge (Institut f�r Berufliche Entwicklung, 164 p.)

4. Measurements at Lighting Installations

4.1. General Remarks

According to the measuring principle, similar instruments are applied to the measurement of illuminance and luminous density.

These are always physical measurements.

The photoelectric receivers are photoelements, photoresistors, photodiodes, photomultipliers and others. Their spectral sensitiveness is various and not congruent with the photopic eye response curve. For the correct measuring of illuminance and luminous density values, however, it is necessary that the photoelectric receivers evaluate the light in the same way as the human eye. Therefore, the sensitiveness of the physical receivers must be adapted.

Mostly, this is achieved by filters, but it can also be realized by diaphragm mechanisms. Of course, with supplementary filters and diaphragms, a reduction of the irradiated light energy is connected; the better the adaptation is the greater becomes the mentioned reduction. Generally, it is compensated by electronic intensifiers.

Since the required measuring accuracy for lighting installations is not very great - it is between 1 and 5 % - only approximate adaptations are practised. For this reason, correction factors are indicated on some measuring instruments.

When working with physical receivers, attention must also be paid to the ambient temperature. Sensitiveness alters with higher or lower ambient temperature. Therefore, the receiver must either be thermo-stabilized or this dependence on temperature must be counteracted by correction curves. An especially great importance for the correct assessment of the incident luminous flux is the direction from which the light hits the physical receiver.

An exact measurement is possible only with vertically incident light.

4.2. Illuminance Measuring

From the general requirements on physical measuring procedures it derives that the following requirements must be met by illuminance measurements:

- Adaptation of the physical receiver to the photopic eye response curve.

- An adaptor for the receiver for the cosine-true measurement of the incident light.

- As far as possible, linear correlations between illuminance values and indication value of the measuring instrument or correction curves for the individual measuring ranges.

- No influence of the measured value by fatigue of the receiver or by its ambient temperature.

When carrying out measurements, make sure that the measuring instrument and/or its photoelectric receiver is not shaded partially or completely by people or things.

The selection of the measuring points is determined by the measuring task. If the value of illuminance shall be measured in certain check points, make sure that the measuring conditions are the same as with previous measurements. If, for example with a project to be handed over, the average illuminance values shall be measured for comparison with the values demanded by the plan, a great number of measuring points has to be fixed the measuring height of which shall generally be 850 mm above the floor and with which the receiver element must be placed horizontally. The size of the measuring errors has to be chosen in such way that it can be supposed that the illuminance value is constant in each measuring field. This leads to the number of measuring points for the space or part of space to be measured.

However, there shall be at least 9 points.

With the measurements the mains voltage has to be checked during the measuring process and indicated in the measuring record.

4.3. Luminous Density Measuring

For measuring the luminous density (surface brightness) also measuring instruments for illuminance may be used if simple additional instruments are applied. It goes without saying that the general requirements in connection with illuminance measuring instruments also apply to luminous density measuring. In this context, attention has to be paid that the receiving area is illuminated as evenly as possible. For the image formation of the surfaces to be measured a luminous density attachment with or without optical system is used.

These kinds of luminance meters are especially suited for measuring floodlighted or transilluminated areas and not for measuring the luminous density at lamps and lighting fittings.

For measurements in interior spaces devices of a wide angular aperture are preferred, because - as is known - the medium luminous density in the field of view determines the adaptation of the human eye. Decisive for the adaptation conditions are the surrounding surfaces which are covered by an angle of view of 30 to 50 degrees. If from a number of areas of different luminous density the average value of the luminous density of all the areas shall be calculated, the areas have to be measured individually.

Questions for repetition and knowledge test

1. On what basis do the luminance meters work?
2. What are the measuring methods for measuring illumination installations?

Lighting Installation - Basic vocational knowledge (Institut f�r Berufliche Entwicklung, 164 p.) 5. Light Sources for Illuminating Purposes 5.1. General Remarks 5.2. Thermal Radiation Lamps 5.2.1. Genera1-Service Lamps 5.2.2. Shaped Lamps for Technical and Decorative Purposes, Tube Lamps 5.2.3. Projection Lamps 5.2.4. Halogen-Filled Incandescent Lamps 5.3. Discharge Lamps 5.3.1. Low-Pressure Lamps (introduction...) 5.3.1.1. Tubalar Fluorescent Lamps 5.3.1.2. Sodium Vapour Lamps 5.3.2. High-Pressure Lamps (introduction...) 5.3.2.1. Mercury-Vapour Lamps 5.3.2.2. Halogen Metal Vapour Lamps 5.3.2.3. Sodium Vapour Lamps

Lighting Installation - Basic vocational knowledge (Institut f�r Berufliche Entwicklung, 164 p.)

5. Light Sources for Illuminating Purposes

5.1. General Remarks

According to the kind of light generation, the light sources are divided into two groups:

- Temperature radiators and
- Discharge lamps.

The group of temperature radiators includes all universal lamps, projection lamps and halogen lamps. These light sources have a great infrared portion and only a small visible range (approximately 90 % of the power rating is heat and 5 - 10 % is visible light). Consequently, the light efficiency is very low.

The discharge lamps comprise the group of low-pressure discharge lamps which the fluorescent lamps and sodium vapour discharge lamps (low-pressure lamps) belong to as well as the group of high-pressure discharge lamps which include the high-pressure mercury vapour lamps, halogen metal vapour lamps and high-pressure sodium vapour lamps. This categorization of lamps is of an increasing importance.

5.2. Thermal Radiation Lamps

5.2.1. Genera1-Service Lamps

Construction forms for illuminating purposes

Figure 17. General-service lamps

Base: Screw-thread or bayonet base

Figure 18. Socket forms for filament lamps

- Bulb: Clear or inside-coated, silvered or with reflector-coating

- Coiled-coil filament: Single or double filament with normal mount or - which is more frequently used - suspension in order to increase the vibration stability and shock absorption

- Gas filling: Argon-nitrogen or krypton-nitrogen mixture

Construction forms for illuminating and decoration purposes

- Bulb: Colour-coated red, orange, yellow, green, blue or pressed patterns or ornaments on the external surface of the bulb

Way of acting

The bulb, after application of its operating voltage, takes a higher current from the mains (starting current) than it will consume after having reached the operating point. The great current density in the coiled-coil filament with much heat development results in bright incandescence, that is to say in the generation of visible light.

Increased voltages lead to increases in the luminous flux but reduce the service life of the bulb considerably. For example: If the mains voltage rises by 5 %, the service life of the bulb falls to about 55 %, the luminous flux being increased by 20 %. Bulbs are produced of an efficiency up to 2000 W.

Use

- For illuminating purposes

In local lamps, decoration lamps, domestic lighting fittings, lighting fittings for purposes of representation and in technical lamps. Use for industrial purposes was much limited for energetic reasons in favour of the discharge lamps.

- For advertisement and illumination

Here, it is the luminous effect that counts, the light power is of secondary importance. The professional use of such lamps requires knowledge in the field of light effects such as colour stimulation, blending of colours, colour suppression.

Hints to practice

Do not put bulbs into lighting fittings with fatty or sweaty hands. Vibrations in general and shock especially have to be avoided when bulbs are in operation.

With frequent defects of bulbs the mains voltage has to be checked - overvoltages. See also way of acting.

The wear of the tungsten filament requires a replacement of the bulb after the rated lamp life has expired even if it has not become defect by that time. (The energy consumption increases the older the bulb grows).

For a correct order the following bulb details are required: Rated voltage, power rating in watt and/or luminous flux in lumen, type of base and bulb and/or special wishes such as silvering, colour or ornament glass.

In recent time, the development in the field of bulbs has been intensified. Tungsten-halogen lamps - also in the range of low voltages - have been used more and more. Compact and tubular lamps, too, are used frequently. The trend goes towards a lamp of high light power and little energy consumption. Spot lights are often designed on the basis of a low-voltage halogen lamp operated through a small transformer in an E 27 lamp base. The service life is remarkably longer than with traditional lamps.

5.2.2. Shaped Lamps for Technical and Decorative Purposes, Tube Lamps

This group of lamps includes bulb lamps 15 and 25 W, drop lamps 25 to 40 W and large candle lamps 15 to 60 W. These lamps are used for decorative lighting purposes, for smallest lighting fittings as well as for the illumination of refrigerators and switching plants.

Figure 19. Pear-shape lamps

Figure 20. Drop-shape lamps

Figure 21. Large candle lamps

Similar in construction are tube lamps from 15 to 25 W, which are used in various versions as control lamps, sewing machine lamps as well as in small local and decoration lamps.

Figure 22. Tube lamps

5.2.3. Projection Lamps

With projection lamps, the correlation of light efficiency and service life with thermal radiators is applied in favour of the luminous flux. For illumination engineering only a few types are important, among others the A projection lamps the average service life of which amounts to 300 h. The burning position of these lamps has also to be taken into consideration.

Figure 23. Projection lamps

1 length of lamp
2 diameter of lamp

5.2.4. Halogen-Filled Incandescent Lamps

Halogen-filled incandescent lamps due to their way of functioning must be made of quartz glass or hard glass. When using these lamps make sure that certain admissible temperature limits at some parts of the lamps as well as the given burning position are observed.

The main characteristics of the halogen-filled incandescent lamps are:

- Small dimensions
- No bulb blackening
- Constant luminous flux
- Constant colour temperature
- Colour temperature up to 3400 K
- Longer service life
- Higher luminous flux.

Halogen-filled incandescent lamps are prevailing in the fields of film and photo shooting, lighting fittings for motor vehicles, floodlighting and with slide and narrow-gauge film projectors.

Hints to practice

Projection lamps and halogen-filled incandescent lamps are manufactured in the range of 1000 to 5000 W and, according to type, achieve luminous fluxes up to 125.000 lm in the high-voltage range of 225 V.

With the operation of these lamps, the prescribed burning position must be observed by all means.

In any case, the instructions of the manufacturer have to be considered.

5.3. Discharge Lamps

5.3.1. Low-Pressure Lamps

By this term a low power density in the entire discharge space is understood, i.e. the discharge is distributed over the full cross section.

The most important representatives of this group of light sources are the fluorescent lamps and the low-pressure sodium vapour lamps.

5.3.1.1. Tubalar Fluorescent Lamps

Forms

Figure 24. Fluorescent lamps (rod-shape)

- Rod-shaped lamp with bipin caps of 16, 26, 32 and 38 mm in diameter

- Rod-shaped lamp with single-pin caps of 38 mm in diameter (rapid-start lamp)

- U-shape with bipin caps, 26 and 38 mm in diameter

Figure 25. Fluorescent lamps (U-shape)

- Ring-shaped lamp with external ring diameters of 216, 311 and 413 mm and tube diameters of 29 and 32 mm

- Twin tube lamps with the caps G 23, G 24d-1, G 24d-2, G 24d-3, and 2 G11, a tube diameter of 13 mm and a power range of 5 to 36 W.

Figure 26. Twin-tube lamp

Table 16. Utilization factors

Efficiency (See Table 15)

Colours

The manufacturers of light sources have their own colour designations and appertaining code numbers. At present, there is no international standard in this field. The below selected examples shall demonstrate three national colour designations.

Table 17. Survey of three national determinations of colour (arranged according to colour temperature)

The above comparison of various manufacturers of tubular fluorescent lamps shows how difficult it is to realize certain definite aims of illumination only starting from the colour designation. For this purpose, the documentations of the manufacturers are absolutely necessary.

Starting aids, starting mechanisms

Tubular fluorescent lamps need starting aids. Without that the fluorescent lamp cannot be operated.

- Starter for separate switching
- starter for tandem switching
- Electronical starter

Starterless operation is enabled by rapid lamps. Here, the starting aid is a special series-reactor switching device as well as a conductive ignitionstrip alongside of the lamp.

Series reactors

They are required to supply a sufficient ignition voltage and to reduce the mains voltage to the lamp voltage.

There are:

- Inductive series reactors (separately for each lamp power)

- Transistor series reactors (for tubular fluorescent lamps for operation with 12 or 24 V direct current voltage)

- Electronic series reactors (for flicker-free start without starter, GS-operation, light control etc.)

Way of acting

After connection of the lamp, a glow discharge takes place in the starter heating up the bimetal which is situated in the starter. This bimetal bends due to the heat and closes the lamp circuit. Then, the tungsten electrodes are heated up and stimulated to emit electrons. Thus the internal space of the lamp is ionized. Simultaneously, a magnetic field is induced by the current that flows through the ballast. Meanwhile, no glow discharge took place in the starter, the bimetal cools down and opens the circuit. By this, the field of force collapses in the ballast, the lines of force intersect the bobbin inducing a high voltage (up to 1300 V). This voltage is able to overcome the ionized internal space of the lamp from electrode to electrode.

It comes to a gas discharge. The fluorescent layer is stimulated to emit light. After ignition, the ballast fulfills the function of a variational resistor. A portion of the mains voltage drops over the ballast, it remains the portion which is fed into the lamp as operating voltage. The ballast also limits the operating current to the permissible value of the lamp current.

For this reason, only one ballast is allowed to be used for the lamp, which corresponds to the lamp current. Fluorescent lamps can also be operated by direct current voltage, if the lacking a.c. resistance is replaced by an ohmic resistance and the lamp is pole-changed from time to time with the help of an intermediate switch.

Use

Today, fluorescent lamps are used for many purposes. As far as suitable lighting fittings are available, the existing lamp colours and performance parameters allow the use of fluorescent lamps for almost all and every lighting purpose. By the creation of electronic ballasts, the disturbing flickering and dangerous stroboscopical effect of the fluorescent light is eliminated.

However, with the use of fluorescent lamps psychological aspects must be considered, because certain branches of the food, textile and paint industries as well as artistic fields such as painting and graphic arts can make only limited use of fluorescent light due to colour falsification, shadelessness and so on.

Man is emotionally stimulated by colours and coloured light, that is to say, emotions can be influenced. These problems were only very little touched by the bulb.

New in the range of fluorescent lamps are black-light lamps for special effects or detection of colour falsification in paintings, the baby-blue lamp for combatting jaundice with babies as well as the germicid lamp which is used for degerming the air. The lumoflor lamp is used for the acceleration of plant growth.

Hints to practice

The best ambient temperature for fluorescent lamps is 25° centigrade. With increasing ambient temperature, the service life of the fluorescent lamp decreases.

Since the fluorescent lamp is operated by means of inductive ballast, it is an inductively loaded collector that imposes the required blind power on the network, i.e. on all supply lines.

The network can be relieved to a great extent by compensation capacitors which store the required blind power. The following reference values are applicable to fluorescent lamps:

For interference suppressing (elimination of radio interference), suppressor capacitors of 0.022 microfarad/250 C are connected in parallel per lamp at the lamp feeding point (illuminator entrance). Fluorescent lamps are connected as follows:

- Single connection (classical version)

Figure 27. Separate switching of fluorescent lamps

1 switch, 2 series reactor, 3 compensation capacitor, 4 fluorescent lamp, 5 starter, 6 anti-interference capacitor

- Tandem connection

Figure 28. Tandem switching of fluorescent lamps

1 switch, 2 series reactor, 3 fluorescent lamps, 4 starter, 5 compensation capacitor

- Rapid connection

Figure 29. Rapid switching of fluorescent lamps

1 switch, 2 series reactor, 3 compensation capacitor

In addition to these commonly used connections, the below mentioned connection is used:

- Twin-lamp circuit

Figure 30. Dual lamp circuit of fluorescent lamps

5.3.1.2. Sodium Vapour Lamps

Low-pressure sodium vapour lamps, at the time being, have the greatest light efficiency: 183 lm/W. The light efficiency of these lamps is bound to a certain discharge temperature (therefore, a heat reflecting protectice glass is used which keeps the discharge tube at a favourable temperature).

The light is monochromatic yellow, so that no colour seeing is possible. The body colours appear only as shades of grey.

Low-pressure sodium vapour lamps are used in special fields of outdoor lighting such as: express motor roads, trunkroads, crossings, tunnels, waterways, docks and wharves, protection of buildings and/or sites.

Special advantages:

- Best possible penetration of fog and smoke
- Long useful burning life

Shape:

- Tube

Base:

- BY 22

Power and efficiency:

- Electrical 35, 55, 90, 135 and 180 W
- Light 4800, 8000, 13500, 22500 and 33000 lm

Table 18. Supra-national comparison of sodium vapour lamps (arranged according to their rated lamp power and luminous flux)

5.3.2. High-Pressure Lamps

This group includes high-pressure mercury vapour lamps, halogen metal-vapour lamps, and high-pressure sodium vapour lamps.

5.3.2.1. Mercury-Vapour Lamps

High-pressure mercury vapour lamps thanks to their specific advantages have become the preferred kind of lamps for outdoor lighting. The permanent improvement in the quality of colour rendition and the advantages of a great luminous flux per lamp unit contributed to the introduction of these lamps also into many fields of indoor lighting.

The light efficiency of high-pressure mercury vapour lamps is between 40 and 60 lm/W.

Figure 31. High-pressure mercury lamp

Construction

- Exterior glass bulb ellipsoid or fungiform transparent or inside-coated with or without reflecting layer

- Internal quartz bulb (also called burner) with sealed-in electrodes and auxiliary electrodes

- Base

E 27/30; E 40/45

- Burner

The burner together with the ignition resistors is suspended in a holding element in the exterior bulb.

The space between the burner and the exterior bulb is air-thinned.

Way of acting

If and when an operating voltage is applied, a glow discharge takes place between the auxiliary and main electrodes which results in the development of heat. The heat leads to the evaporation of the quantity of mercury which is situated in the burner as well as to an increase in pressure in the burner in general. The ignition resistors - see circuits - limit the ignition current. The evaporated mercury renders the entire internal space of the burner conductive. A discharge between the main electrodes takes place. Heat and pressure continue to grow up to the point when the mercury vapour settles as a metallic deposit on the internal side of the burner. The discharge arc between the two main electrodes stands now and is stable. The light produced by it leaves the burner with a great proportion of UV.

The external glass bulb filters the detrimental ultraviolet radiation and - by means of its internally deposited fluorescent coating transfers the radiation of the burner into visible light.

The air-thinned internal space of the lamp keeps the operating temperature nearly constant.

In case of an interruption of current the lamp goes out until the internal pressure of the burner on the basis of the mercury deposited on the internal wall of the burner allows a new evaporation. The ignition process starts again. The initially great starting current is limited on the one hand by the ballast and on the other hand by the increasing burner resistance. After approximately 4 to 5 minutes the lamp has achieved its nominal values and an operating pressure of approximately 8 to 10 at in the burner.

Circuit

Figure 32. Circuit of the high-pressure mercury lamp

1 secondary electrode, 2, 4 ignition resistor, 3 burner, 5 main electrode, 6 external bulb, 7 series reactor, 8 switch, 9 compensation capacitor, 10 lamp

Hints to practice

The burner position is any you like. The lamp parameters, however, apply to the burner position ‘vertical’ (base on top). With horizontal position only 97 % of the luminous flux are achieved.

The lamp is nearly independent of ambient temperatures and therefore is ideal for open-air installation. The lamp life is between 5000 and 10.000 hours.

Table 19. Supra-national comparison of high-pressure mercury vapour lamps (arranged according to their rated lamp power and luminous flux)

Clear-glass bulb lamps are used for copying machines (heliographic printing).

For outdoor lighting, high-pressure reflecting lamps are used. In indoor lighting, lamps with elliptic bulbs with oxidic internal reflector are used. The coating of the external bulb can have different colour variants.

Special attention has to be paid that high-pressure mercury lamps in no case are operated without external bulb, that is to say the burner alone. The UV-light which leaves the burner destroys the retina of the human eye.

In fields where a light failure of several minutes may cause an accident equal filament lamps have to be installed in addition to the high-pressure mercury vapour lamps (mixed light). The lamp should be suspended at such height that dazzling by direct light incidence is avoided.

The high-pressure mercury vapour lamps must be compensated because of their inductive power.

When several lamps are used attention has to be paid to a symmetrical network distribution. Compensation capacitors are assigned as follows:

50 W: 7 microfarad/220 V
80 W: 8 microfarad/220 V
125 W: 10 microfarad/220 V
250 W: 18 microfarad/220 V
400 W: 25 microfarad/220 V
700 W: 40 microfarad/220 V
1000 W: 50 microfarad/220 V
2000 W: 50 microfarad/220 V

5.3.2.2. Halogen Metal Vapour Lamps

Halogen metal vapour lamps, by their great light efficiency of 75 to 90 lm/W, the great luminous flux concentration and good colour rendition, are of increasing importance in lighting engineering in the fields of colour television and colour film.

Table 20. Supra-national comparison of halogen metal vapour lamps (arranged according to their rated lamp power)

Construction

The structure of halogen metal vapour lamps, in its essence, is similar to that of the high-pressure mercury vapour lamps. The lamps have a tube-shaped or elliptic clear-glass external bulb.

Figure 33. Halogen metal vapour lamp

Some kinds of these lamps have a layer of luminescent material which, among others, serves to adapt the luminance and light distribution to that of the high-pressure mercury vapour lamps.

By admixing certain additional luminescent materials to the high-pressure mercury discharge in the form of metallic halides the gaps in the mercury spectrum are filled, which explains the great light efficiency and good colour rendition of these lamps.

Admixtures are - according to the respective type of lamp - iodides of sodium (Na), thallium (TI), indium (In) and lithium (Li).

Halogen metal vapour lamps are characterized by a very adaptable spectrum. Among others, for example, lamps can be manufactured emitting radiation only in the green or blue colour ranges.

Way of acting

Halogen metal vapour lamps need approximately 2 to 3 minutes till they achieve their electrical and technical characteristic values. The restarting time is about 10 to 15 minutes. In view of the restarting time of 10 to 15 minutes, it is recommendable to operate the lamps through time-delayed relays. These relays disconnect the operating voltage in the case of short voltage failure which extinguishes the lamp and reconnect it only after the time mentioned. This preserves the ignition mechanism.

Circuit

Halogen metal vapour lamps are operated by alternating current voltage of 220 V for lamps up to 400 W and by 380 V for lamps from 1000 to 2000 W at a voltage tolerance of 5 %. With colour film or colour television shooting the tolerance of +- 10 V should not be exceeded in order to keep up the quality of colours. In addition to the ballast, an ignition is required to start the discharge. For this purpose, starter ignition sets as well as a thyristor ignition set are used.

Figure 34. Circuit of halogen metal vapour lamps

1 series reactor, 2 ignition set, 3 lamp

Hints to practice

The burner position of the lamp is any you like. An exception is only the horizontal position with a deviation from position of maximally +- 2 %.

The luminous flux is independent from the ambient temperature.

Lamps for vertical position of use have approximately 5 % greater luminous fluxes. Changes in network voltage cause colour changes of the lamp, for instance, undervoltages tend to the blue-green range of colour, overvoltages to the yellow-orange one.

That means that the colour temperature changes!

The service life is between 1000 and 6000 hours, according to the type of lamp.

Compensation capacitors are assigned as follows:

175 W: 18 microfarad/220 V
250 W: 18 microfarad/220 V
400 W: 25 microfarad/220 V
1000 W: 30 microfarad/380 V
2000 W: 50 microfarad/380 V

5.3.2.3. Sodium Vapour Lamps

High-pressure sodium vapour lamps have gained international importance within a relatively short time. Mainly, this is the result of the great light efficiency values compared with other high-pressure discharge lamps - with some types it is more than 100 lm/W. Taking the respective conditions of use into consideration, very economical lighting solutions can be found with the help of these lamps. For example, the luminous flux of a high-pressure sodium vapour lamp of 250 W is equal to that of a high-pressure mercury vapour lamp of 400 W.

Another advantage in addition to the great light efficiency consists in the little decrease of the luminous flux in the course of the lamp life.

Figure 35. High-pressure sodium vapour lamp

Construction

Way of acting

The starting time is 4 to 5 minutes. Reignition is possible after 1 minute already.

This lamps needs a series reactor and a starting set for being started.

After application of the network voltage, the starting set gives ignition pulses to the discharge enclosure (approximately 1500 V). After ignition, a bimetal switches a the starting set off. In the discharge enclosure, the temperature rises to 1200 degrees centigrade and a pressure develops of approximately 13000 Pa. The most similar colour temperature is 2100 K.

Circuits

Figure 36. Circuit of high-pressure sodium vapour lamps

1 switch, 2 compensation capacitor, 3 series reactor, 4 ignition set, 5 lamp, 6 ignition lead

Hints to practice

This lamp should be used as follows:

- Street lighting
- Building floodlighting
- Lighting of pedestrian crossings and car parks
- Port installations
- Container stations
- Railway trackages
- Large building sites
- Open-air industrial areas
- Sports fields.

In the field of indoor lighting, this lamp can be used for foundries, cement works, storing and assembly halls. The lamp must be compensated. The following values are recommended:

175 W: 25 microfarad/220 V
250 W: 33 microfarad/220 V
400 W: 50 microfarad/220 V

The service life amounts to approximately 8000 hours.

The burning position is any you like. The luminous flux depends on the ambient temperature.

Questions for repetition and knowledge tests

1. How are the light sources categorized?

2. What forms, diameters and performances do low-pressure fluorescent lamps have?

3. How can fluorescent lamps be started?

4. What are the most commonly used lamp circuits?

5. What are the tasks of the series reactor?

6. What are the advantages of the low-pressure sodium vapour lamp?

7. What is the structure of the high-pressure mercury vapour lamp? (The structure has to be described from inside outwards.)

8. What are the advantages and disadvantages of a high-pressure mercury vapour lamp?

9. If the light emitted by a metal-vapour halogen lamp tends much to the blue-green range, this is traceable to a technical mistake. Name the mistake!

10. Describe the structure of a high-pressure sodium vapour lamp from inside outwards.

Lighting Installation - Basic vocational knowledge (Institut f�r Berufliche Entwicklung, 164 p.) 6. Operating Components for Discharge Lamps 6.1. Ballast 6.2. Starter Switches 6.3. Ignition Sets 6.4. Compensating Capacitors 6.5. Intensity Control of Lamps

Lighting Installation - Basic vocational knowledge (Institut f�r Berufliche Entwicklung, 164 p.)

6. Operating Components for Discharge Lamps

6.1. Ballast

With discharge lamps, the appropriately dimensioned ballast is an important precondition for the achievement of the lamp life. If a ballast is used which does not correspond to the respective lamp, the lamp parameters may not be achieved and the service life of the lamp may be reduced.

The ballast must have sufficient temperature conditions for the case of use they are meant for. These are printed on the ballast. For example: 105/55/140.

The meaning of these numbers is in succession: Winding limiting temperature in degree centigrade, winding overtemperature in degree Kelvin in normal and anomalous operation.

In normal operating conditions, ballasts in permanent operation with the winding limiting temperature have a service life of 10 years. If the ballasts are operated in anomalous conditions, at the limit of the then occurring winding overtemperature, their service life expires after 20 days. Towards the end of the service life, the ballasts fail due to break, interturn short-circuits or body contact. With this, very high temperatures may occur on the contact surfaces.

In the case of anomalous operation - for instance with preheating of the lamp electrodes - and with 110 % of the rated voltage for ballasts for lamps up to 400 W, the maximally occurring current is limited to the 2.1-fold value of the rated lamp current with lamps of greater power to the 2.2-fold value of the rated lamp current.

Figure 37. Series reactor for fluorescent lamps

Figure 38. Series reactor for high-pressure mercury vapour lamps and halogen metal vapour lamps

Figure 39. Series reactor for high-pressure sodium vapour lamps

6.2. Starter Switches

Starters consisting of the major components of glow starter and capacitor are in important operating means of fluorescent lamps and recently in special designs have also been used as starters for ignition sets.

The prolonged first make time for instance of the St l glow starter for fluorescent lamps is within the range of 0.45 to 2 s; with most starters it is 1 s on an average. The maximum voltage produced is more than 400 V, the test service life 6000 (number of switchings).

For tandem operation of fluorescent lamps of 20 W special starter switches are required.

For starter ignition sets of high-pressure discharge lamps a special glow starter without capacitor is used.

Figure 40. Starter for fluorescent lamps

6.3. Ignition Sets

Halogen metal vapour lamps and high-pressure sodium vapour lamps need ignition sets for starting the discharge. Two different types of sets are available for the user - the starter ignition sets and the thyristor ignition sets.

Starter ignition sets, in their essence, consist of a special glow starter with a current-limiting capacitor and, perhaps, a protective resistor connected in series, by which - including the inductivity of the ballast - the required glitches from 1.5 to 2.5 kV are generated in the form of irregular pulses.

Starter ignition sets are very economical as to the price; they meet the requirements of the IP54 protective system and can be placed at a distance from the lamp.

After ignition of the lamp there is no internal consumption. As a wearing part the starter is considered as disadvantageous its replacement requiring much maintenance work.

The thyristor ignition set is an electronic heterodyne ignition set and consists of various semiconductor elements as well as of a pulse transformer. The primary voltage of the pulse transformer is switched by a thyristor controled by a diac.

The high-voltage pulses of approximately 4.5 kV and a natural frequency of 100 kHz which develop at the secondary winding of this transformer are superimposed on the network voltage near the maximum of the positive half-wave. Ballast and secondary winding of the pulse transformer are connected in series with the lamp, i.e. the lamp current flows over the secondary winding which is designed for a continuous current load of 4.4. A. From this results the power loss of the ignition set of maximally 4 W with the lamp burning. The high tension is led out by an ignition wire which has to be connected with the contact plate of the socket. The short ignition wire conditional on the set requires the ignition set to be arranged near the socket of the lamp. After having ignited the lamp the ignition set gives no further high-voltage pulses; however, it continues to work if and when the lamp is defective or the lighting outlet is unoccupied (continuous ignition).

6.4. Compensating Capacitors

The current limitation by inductive ballasts with discharge lamps causes a power factor of 0.4 to 0.7 according to the type of lamp; the average is 0.5 approximately. The use of suitable capacitors enables an improvement in the power factor - about 0.85. MP-compensating capacitors (parallel capacitors) of 2 to 40 microfarad as well as motor and power capacitors are used.

Furthermore, it is distinguished between single power-factor compensation, group power-factor compensation in alternating current installations and three-phase current installations and central power-factor compensation. The last mentioned kind of compensation considers all inductive consumers of the entire generating plant by a battery of capacitors based on an automatic control by connecting and disconnecting individual capacitors depending on the power factor measured. The capacity values of single compensation are to be found in the respective tables.

Compensation capacitors are connected in parallel to the network and must be disconnectable together with the entire installation. If a number of single capacitors are used in order to achieve the total capacity, these must be connected in parallel.

6.5. Intensity Control of Lamps

With all-purpose lamps intensity control can easily be realized.

By a voltage dip of only 30 %, a luminous flux value of 1 % can be achieved. This is done by using series resistors or - more economically - by adjustable transformers. Modern electronical small devices on thyristor basis are known as dimmers.

With fluorescent lamps, due to the falling characteristic of the current-voltage-dependence and the required high reignition voltage, an intensity control by reducing the voltage (amplitude control) is not possible.

Here, the principle of phase-shifting control is applied, i.e. the lamp current and thus the luminous flux are changed in a wide range both half-waves being used. The best control behaviour is shown by rod-shaped fluorescent lamps of 40 W, which must be equipped with an ignition aid in the form of an earthed starting strip or a closely spaced ignition grid. In addition to the ballast, each lamp needs a heating transformer with two separate secondary windings for preheating the lamp electrodes. The heating transformer, for instance 220 V/2 x 6.3 V, 10 VA and the device for the phase-shifting control must always be connected to the same external conductor. Because of the low preheating voltage of about 6 V, attention has to be paid that the lamp sockets give faultless contacts. In order to improve the quality of control, an ohmic base load has to be connected to the load exit of the device according to the instructions of the manufacturer (e.g. filament lamps 25 W).

To one light-controlling device, several lamps can be connected according to the design of the device.

The regulating proportion that can be achieved is in the range of 1:20 to 1:30; in favourable conditions a ratio of 1:100 is possible. Before using fluorescent lamps for intensity control the entire lot of lamps of one charge should be burnt in for approximately 20 hours.

Figure 41. Intensity control of fluorescent lamps

1 control unit
2 series reactor
3 filament transformer
4 lamp
5 ignition strip

To high-pressure mercury vapour lamps the above mentioned methods cannot be applied, because a voltage dip of more than 15 % already leads to the extinction of the lamp or to unstable operation.

Questions for repetition and knowledge tests

1. What are the distinguishing characteristics of ballasts of fluorescent lamps compared with ballasts of high-pressure mercury vapour lamps?

2. Why are compensation capacitors required for discharge lamps?

Lighting Installation - Basic vocational knowledge (Institut f�r Berufliche Entwicklung, 164 p.) 8. Lighting Fittings (introduction...) 8.1. Protection Classes 8.2. Degrees of Protection 8.3. Efficiency of a Fitting 8.4. Kinds of Lighting Fittings (introduction...) 8.4.1. Functional Lighting Fittings for Indoor Lighting 8.4.1.1. General Lighting Fittings 8.4.1.2. Local Lamps 8.4.1.3. Flameproof and Explosion-proof Lighting Fittings 8.4.2. Outdoor-Lighting Fittings 8.4.2.1. Street Lighting Lanterns 8.4.2.2. Decorative Outdoor-Lighting Fittings 8.4.2.3. Floodlights and Spotlights 8.4.3. Lighting Fittings for Representation Purposes and Housing Space 8.4.4. Lighting Fittings for Special Purposes

Lighting Installation - Basic vocational knowledge (Institut f�r Berufliche Entwicklung, 164 p.)

8. Lighting Fittings

Lighting fittings are devices serving the distribution, filtering and transformation of light emitted by lamps. They included all parts necessary for fitting, protecting and operating the lamps.

According to the effect of light it is distinguished between two main groups:

- Lighting fittings for illumination purposes
- Lighting fittings for light emission.

Within these groups, the actual subdivision is made according to the respective purposes of use. If one tried to designate all lighting fittings by these very few names, this would soon lead to difficulties of distinction. Therefore, further subdividing of lighting fittings is made, for instance by the mode of their installation or placing.

Table 23. Classification of the lighting fittings according to the ways of fixing

Stationary fittings

Mobile fittings

All lighting fittings used for illumination purposes have to meet definite requirements as to lighting engineering, design, electrotechnical and mechanical qualities. These requirements have more or less importance according to the purpose the respective lamp shall fulfill. With domestic rooms and rooms for representation, for example, demands will be made mainly on the design of a lighting fitting. Shall the lighting fittings contribute to the interior decoration of a room, this is to say they shall be included in the architecture, demands of illumination engineering should rank first. With working lighting fittings, technical requirements are decisive and the design is subordinated to them. The term of working lighting fittings is not standardized, neither nationally nor internationally. However, it is used in this textbook for better distinction from domestic lighting fittings and those for representation purposes.

8.1. Protection Classes

The protective class of a lighting fitting indicates the protective measures or the integration into the protective measures against hazardous contact voltage during the installation of the lighting fitting.

All lighting fittings must be constructed in accordance with the protective classes I, II or III. For external marking on the lighting fitting, the symbol is used for protective class II, while symbol applies to protective class III.

Table 24. Electric lighting fittings

There is no special marking for lighting fittings belonging to protective class I.

The international trend goes to the application of protective class II to lighting fittings that can be installed and maintained by amateurs. This concerns especially the domestic lighting fittings. But also with working lighting fittings the use of the protective insulation leads to greater safety and, with some installations, even to material savings.

The protection classes mean:

Table 25. Degrees of protection of lighting fittings