ARTIFICIAL LIGHTING lecture notes

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1 ARTIFICIAL LIGHTING lecture notes Dr. Habil. András Majoros Figures, images and tables by Levente Filetóth Budapest University of Technology and Economics Faculty of Architecture Department of Building Energetics and Services Prof. András Majoros: Artificial Lighting 1.

2 LIGHTING AND THE VISUAL ENVIRONMENT THE COMPONENTS OF THE VISUAL ENVIRONMENT The goal of lighting is to make the environment visible, the visual environment is a visible environment. The aim of lighting is to create an adequate visual environment. The internal visual environment comes into being by illuminating a room. Thus, there are two components of the visual environment - one is a usually furnished room with surfaces reflecting light to a greater or lesser extent, - this is a basically passive component- and - the other is light, which (as an active component) makes the room visible. The surfaces of the interior can be characterized by their reflectance, while the use of light can be described by the illuminance of the surfaces. LIGHT AND ITS QUALITY Light is the visible part of the electromagnetic spectrum between the wavelengths of l = nm. Its symbol is Φ e, its unit is Watt [W] Each wavelength corresponds to a given colour as shown in the following figure. Colours at shorter wavelengths are called cool (colours like purple and blue), colours at longer wavelengths are called warm colours (like orange and red). We use so called white light for lighting, as the natural light that human vision developed by was white light, too. It is a peculiarity of white light that it contains radiation at every wavelength of the visible range, and that the intensity of radiation at the different wavelengths vary to a certain extent. Thus, white light may vary. White lights differ from each other in colour combination, so white lights may differ in quality. The quality of white light can be characterized with its spectral distribution. There are two aspects of the quality of light that are important in practice. The quality of white lights may differ because they may contain consecutive colours in varying ratios. The quality of a white light can be characterized in practice from this point of view with the help of colour temperature. The colour temperature of a given light is the temperature of the black Prof. András Majoros: Artificial Lighting 2.

3 body, at which the spectral distribution of its radiation is nearly the same as that of the given light, its symbol is T, its unit is Kelvin [K]. A lower colour temperature means warmer light, a higher colour temperature indicates cooler light. The ratio of red is higher in warm light, while the ratio of blue is higher in cool light. The colour temperature of the incandescent lamp shown in Figure 0.2 is K. The quality of white light may also vary according to how much the colour of the surfaces illuminated by the light appear to be different when illuminated by artificial light compared to the colour they appear to be when illuminated by natural light. From this point of view, the quality of white light can be given with the help of colour rendering. The better the colour rendering of a white light, the less difference the colour of the surface shows when illuminated by it and by natural light. The degree of colour rendering can be given with the help of the colour rendering index in %, whose symbol is R a. R a = 100 % when colour rendering is perfect. Prof. András Majoros: Artificial Lighting 3.

4 THE QUALITIES OF SURFACES The reflection of surfaces can be characterized in an exact way by the reflection factor expressed as a function of wavelength ρ(λ). Surfaces can be classified into two groups: 1. The group of non-coloured surfaces. It is typical of these surfaces that they reflect nearly the same portion of light at every wavelength as shown in the following figure. When illuminated with white light, that is to say with a light containing all the colours in nearly the same proportion, these surfaces seem white, black or various shades of grey. 2. The other is the group of coloured surfaces. It is typical of these surfaces that their reflection varies greatly at different wavelengths. As wavelengths correspond to colours, the above surfaces seem to be the colour at whose range their reflection is dominant when illuminated with white light. Prof. András Majoros: Artificial Lighting 4.

5 It is essential to note that the colour of a given surface is not an inherent quality, existing independently of everything, but it is a quality affected by both the characteristics of the surface and the quality of the light that illuminates it. Consequently, what colour a surface seems to be depends on the colour distribution - the quality - of the illuminating light as well. Still, people attribute natural colours to materials. Those are the colours the materials have by natural lighting. As natural light is a white light, and its quality may vary, people associate many different natural colours with a given material. The colour of a surface is the perception generated by the spectral distribution of the light reflected from it Φ ρ (λ). It depends on the reflection factor of the surface as a function of wavelength - ρ(λ) - and on the spectral distribution of the illuminating light - Φ i (λ) as illustrated by the following equation Φ ρ (λ) = ρ(λ) * Φ i (λ) The colour of a given surface may vary. The colours associated to surfaces (materials) in our minds are the colours that they seem to have by natural lighting, so - grass is green, as natural light contains all the colours, including green, grass reflects the green part of the light, and absorbs the rest of the light. The same grass is practically black if it is illuminated with red light. - milk is white, as it reflects every part of the natural light in nearly equal measure, so the reflected light is white light. When milk is illuminated with red light, it reflects only red light, and it looks red. The spectral distribution of natural light is always changing, the components of direct sunlight, of the light of an overcast sky, that of a clear or partly cloudy sky are different, and different colours are present in these lights to differing degrees. As a result, different natural colours are associated with the surfaces and materials of the environment. We consider grass green by different sky conditions, whether the sun shines or not. Prof. András Majoros: Artificial Lighting 5.

6 THE CHARACTERISTICS OF THE VISUAL ENVIRONMENT We see the elements of our environment as having some colour and brightness. The brightness of a surface is the so called L luminance. The lighter the surface, the greater its luminance is. In a word, it is the luminance and the colour of certain elements of the surfaces we perceive. The greater the reflection (ρ) and the illuminance (E) of a surface is, the lighter it is, in other words L = ρ * E The visual environment is the spatially arranged surface elements of our field of view, that is Σ (field of view) ρ * E The visual environment is a product of the passive environment (ρ) and of active illumination (E). The two components are inseparably involved in the result. The brightness of a darker, but better illuminated surface may be the same as the brightness of a dimly illuminated lighter surface. To sum it up, the visual environment is a three dimensional coloured image of the field of view, a spatial arrangement of luminances and colours. It follows from the fact that the visual environment is a product of the environment and of illumination, that -a good visual environment is a product of a well formed interior and of adequate illumination, -neither a badly formed environment, nor inadequate illumination, can result in a good visual environment. The goal of lighting is to create an appropriate visual environment. What constitutes an adequate visual environment can vary from case to case. The visual environment has to meet a double requirement: -on the one hand, we require background information from our environment, we would like to know what is, and what is happening around us. This requirement has to do with the actual field of view. -on the other hand, we require a more or less accurate picture of a certain part of our environment. This requirement is based on the activity done in the room, and it has to do with the centre of the field of view. Usually the latter requirement, the requirement to see details clearly is more exacting. Being able to get exact information on the environment means being able to differentiate the dimensions, luminances, colours and spatial positions of the details. Prof. András Majoros: Artificial Lighting 6.

7 THE CHARACTERISTICS OF VISION The visual environment is created for people, therefore its peculiarities have to be taken into account when forming it. From the point of view of lighting, the following qualities of human vision have to be taken into account : 1. Human eyes can see nearly a hemisphere, but only a relatively small part of it, in the axis of the field of view, is perceived exactly. 2. We can see colours only in light environments. If it is dark, we can only see the environment in black and white. 3. The sensitivity of the human eye depends on the wavelength (colour) of the perceived light as shown in the figure of V λ (λ). If the intensity of the radiation reaching the eye is the same at every wavelength, we perceive as the lightest colour - the yellow-green colour at 555 nm in a light environment, - the blue-green colour of 505 nm in a dark environment. The name of V λ (λ) is the curve of spectral luminous efficacy. Prof. András Majoros: Artificial Lighting 7.

8 It follows from the above, that light seen by the eyes, as a physical effect, is not the same as the luminous flux, the sense of light. The luminous flux is the part of radiant light that produces a visual impression, its symbol is Φ, its unit is lumen [lm]. Although only the term of "luminous flux" should be used, the term "light" is often used carelessly in everyday practice. 4. The human eye can adapt its sensitivity to light. This process is called adaptation. Different levels of adaptation correspond to environments lit to various degrees. The adaptability of vision does not mean we are able to see equally well in every environment. Our vision is better in brighter environments than in darker environments. When the environment changes, when it gets brighter or darker, our vision has to adapt to it, which takes time. The time required for full adaptation is nearly one hour. 5. We are able to see clearly objects at various distances. This quality of vision is called accommodation. 6. We perceive the ratios of brightness logarithmically. Consequently, - relatively unevenly illuminated homogeneous surfaces seem to be of nearly the same brightness, - nearly evenly illuminated, non-homogeneous surfaces seem more homogeneous, - in order for a surface to be twice as bright as another, the ratio of their brightness has to be 1:10. Prof. András Majoros: Artificial Lighting 8.

9 THE VISUAL TASK AND THE VISUAL ENVIRONMENT When forming an adequate visual environment, two essential questions have to be answered:. 1. What constitutes an adequate visual environment in the given circumstances? 2. How can the visual environment be made adequate? The question of "What constitutes an adequate visual environment in the given circumstances? " can be answered on the basis of the characteristics of vision and on those of the visual task originating from the activity performed in the interior. A given visual task requires a certain visual ability. Visual ability is the accuracy and speed of visual processing. The measurable parameters of visual ability are the following: - visual accuracy, - contrast sensitivity and - speed. Visual accuracy is the reciprocal of the minimum angle α min, at which two points can be differentiated from each other. Contrast sensitivity is the reciprocal of the minimum contrast C min that can be perceived. Speed is the speed of visual processing. Visual ability is affected by the visual environment. The visual environment is characterized by its average luminance. The conditions of a well-defined visual ability are a product of a certain level of average luminance of the visual environment. In order to achieve the desired visual ability, the visual environment, as a possible field of view, has to have a certain level of average luminance. Prof. András Majoros: Artificial Lighting 9.

10 The relationship between the characteristics of visual ability and the average luminance of the field of view is illustrated by the following figure. In any visual task, the size of the part of the object to be seen as well as the distance between the object and the viewer defines a minimum angle of α *. That is the minuteness of detail we have to see the object with in order to get adequate information. The visual environment has to provide a visual accuracy appropriate for 1/ α *. Prof. András Majoros: Artificial Lighting 10.

11 Contrast C * between the brightness of an object and its surroundings defines a contrast sensitivity of 1/C *, which is required in a given visual task in order to get the correct visual information. The above two parameters (1/α * and 1/C * ) determine the minimum visual ability for a given task. As the above figure shows, the average luminance of the field of view has to be a L * t hat is larger than both L α * and L c *. How can the visual environment be changed to achieve an adequate L *, as the average luminance of the field of view? As the luminance of a surface is the product of the reflection factor (ρ) and the illuminance (E) of the surface, i.e. L = ρ * E the luminance of certain elements of the field of view can be changed either by changing the reflectance of the surfaces, or by changing their illuminance. Lighter surfaces and higher illuminances equally result in better visual ability, that is to say, they enable us to perceive smaller details and smaller contrasts. Moreover, it follows from the above equation that there are two ways of changing visual ability and/or the visual environment: - one is changing the ρ reflectance of the surfaces architecturally, - the other is changing the illuminance E by means of lighting engineering. The interior space is usually given prior to designing its lighting system. Consequently, it is the duty of lighting to provide an adequate visual environment (visual ability - average luminance of field of view) for a given activity or visual task. Prof. András Majoros: Artificial Lighting 11.

12 In order to provide the surfaces of a room with adequate illuminance, it is necessary to "put" enough light into the room. The amount of luminous flux generated and distributed in the interior has to be sufficient to illuminate certain surfaces to the required degree. LIGHT SOURCES Light sources are instruments of producing light. Light sources are technical devices which convert usually electric energy into radiation - partly to light. Based on the way they work, light sources are divided into two types of lamps: - incandescent, and - luminescent. In incandescent lamps, light is produced by the radiation of a filament at high temperature. The spectrum of the light generated in this way contains radiation at every wavelength and its spectrum is monotonous. A considerable amount of heat is generated at the same time as light. Incandescent lamps used in practice are - filament incandescent lamps, - tungsten halogen lamps for mains voltage, and - low voltage tungsten halogen reflector lamps. In luminescent lamps light is generated by excited electrons. An electric arc excites light in a socalled arc tube or on the surface of the envelope, as the case may be. The spectrum of the light generated this way is not necessarily continuous, radiation is much larger in certain narrow bands than in others, and the spectrum is not monotonous. Luminescent lamp used in practice are - fluorescent lamps, - compact fluorescent lamps, - mercury lamps, - mercury tungsten blended lamps, - metal halide lamps, and - high pressure sodium lamps. From the point of view of their practical use, light sources can be characterized by their: - construction and operation, and their - technical data: rated voltage: is the voltage that the base of the lamp can be connected to for normal operation. In incandescent and main voltage tungsten halogen lamps, it is the same as the rated voltage of the building's network, in other cases it may be different. nominal input: is the electric power consumed by the lamp alone under rated circumstances. If auxiliaries are needed for the operation of the lamp, the input of the light source - auxiliary unit is larger than that of the lamp alone. type of base: the type of technical design by which the lamp is connected to the electric network. measurements: the main measurements of a lamp, (such as diameter, length, etc.,) that are important from the point of view of installation. Prof. András Majoros: Artificial Lighting 12.

13 - the quality of light: spectral distribution: Φ e (λ) the distribution of light. colour temperature: T [K] colour rendering: R a [%] - cost efficiency: luminous efficacy: is the ratio of P r rated input of lamp and the Φ o luminous flux it produces, its symbol is K, its unit is [lm/w] Φ o lm K = P r W Luminous efficacy does not take into account the consumption of the auxiliaries! life time: is the length of time in which 50% of a large group of lamps becomes unfit for service. initial and running costs starting time: is the length of time a lamp needs to reach its total light output after it has been switched on. restarting time: is the length of time a lamp needs to reach its total light output when it is switched on soon after being switched off. temperature values the effects of circumstances on the above characteristics. Prof. András Majoros: Artificial Lighting 13.

14 INCANDESCENT LAMPS Design and operation: Light in an incandescent lamp is produced by a tungsten filament heated by electric current. The red hot tungsten filament (about 2800 K) is in a bulb filled with a noble gas. The electric connection is made possible by a special base at one or both ends. Incandescent lamps convert only about 1/10 of the input into light. Prof. András Majoros: Artificial Lighting 14.

15 There are various designs of incandescent lamps of different forms of bulbs and types of bases. The quality of light: The spectral distribution of light of an incandescent lamp is shown in the following figure. Its colour temperature is low, K, so its light is warm. Its colour rendering is excellent, R a = 1a. Prof. András Majoros: Artificial Lighting 15.

16 Technical data: The rated voltage of incandescent lamps mainly used for lighting interiors is V. Low voltage - 6, 12 and 24 V - lamps are mainly used for safety reasons. The values of rated wattage of normal incandescent lamps are 25, 40, 60, 75, 100, 150, 200, 500, and W. The so-called Edison base, whose symbol is E, is the most commonly used base. E 14, E 27 and E 40 are the various sizes of the Edison base, the most common being E 27. Different bases are used for different rated inputs of lamps as follows: E 14 base is used for W, E 27 base is used for W, E 40 base is used for 150-2,000 W. The luminous flux generated by one incandescent lamp is: ,000 lm. Cost efficiency: The luminous efficacy of incandescent lamps is 6-20 lm/w. Their life time is usually 1,000 hours, but it may be more than double in certain types. Their initial cost is generally low, due to their simple design. Their initial cost per produced luminous flux is the lowest, although the price ratio of certain types may be 1:8. Their running cost per produced luminous flux is relatively high, due to their bad luminous efficacy and their short life time. Operating qualities: Incandescent lamps produce total light practically immediately after they have been switched on. (starting time is <0.1s). They provide total luminous flux without delay when they are switched on immediately after being switched off, or following a break in the voltage of the network (restarting time is <0.1 s). Their life is affected by the voltage of the voltage supply. The larger the voltage, the shorter the lamps' life time. The operating temperatures of the bulb and the base are high. Temperatures at the top of the bulb may exceed 300 o C. Temperatures along the lamps depend on the burning position. Their burning position is optional. Prof. András Majoros: Artificial Lighting 16.

17 REFLECTOR INCANDESCENT LAMPS Technical data: The design and operation of reflector incandescent lamps are the same as those of normal lamps. The difference is that the inner surface of the envelope nearest the base is mirrored, and this part of the bulb has a parabola shape. As a result, the lamp radiates light at a certain angle. Mirrored lamps are made from standard glass or with special glass - the latter are called PAR lamps. Their usual rated wattages are 40, 60, 75, 100 and 150 W, their bases are generally E 27. In reflector lamps, luminous intensity by the axis of the radiation I o and the so-called beam angle are given instead of the luminous flux. The beam angle is the angle of a cone of radiation in which the luminous intensity is 50% of the maximum at the axis I o. The usual values of the beam angle are 12 o, 15 o, 20 o, 25 o, 30 o, 35 o, 40 o and 80 o. Reflector lamps are made either with narrow beams of radiation (called spot lamps) or with wide beams of radiation (called flood lamps). Prof. András Majoros: Artificial Lighting 17.

18 TUNGSTEN HALOGEN LAMPS FOR MAINS VOLTAGE Design and operation: Their design differs from that of standard incandescent lamps in the following ways. The light source is linear, the envelope is made from quartz glass, and the tube contains halogens - hence the name. Bases are situated at both ends of the tube. Their operation is the same as that of standard incandescent lamps. The quality of light: The spectral distribution of their light is practically the same as that of standard incandescent lamps. Their colour temperature is low, 2,800-3,300 K, so the colour of their light is warm. Their colour rendering is excellent, R a = 1a. Technical data: Their rated voltage is generally between V, their rated wattages are 100, 150, 200, 250, 300, 500, 750, 1,000, 1,500 and 2,000 W. They have special bases for electric connection. The luminous flux generated by one lamp is: 1,300-44,000 lm. Cost efficiency: The luminous efficacy of these halogen lamps is lm/w, better than that of standard incandescent lamps. Their life time (2,000-3,000 hours) is longer than the life time of standard incandescent lamps. Their initial cost is generally low, due to their simple design. Their initial cost per produced luminous flux is somewhat (by about 25%) higher than that of the cheapest standard incandescent lamps. Their running cost per produced luminous flux is relatively high, due to their relatively poor luminous efficacy and relatively short life time. Operating qualities: Halogen lamps produce total light practically immediately after they are switched on (starting time is <0.1s). They provide total luminous flux without delay when they are switched on immediately after being switched off, or following a break in the voltage of the network (restarting time is <0.1 s). The operating temperature of the bulb may exceed 300 o C. Their burning position is horizontal 4-15 o. Prof. András Majoros: Artificial Lighting 18.

19 LOW VOLTAGE TUNGSTEN HALOGEN REFLECTOR LAMPS Design and operation: In these lamps, a small light source is built together with a mirror lamp, thus becoming a compact unit for further installation. They operate in essentially the same way as standard incandescent lamps. The quality of light: The spectral distribution of their light is the same as that of standard incandescent lamps. As a result of the special mirror design, their heat radiation per light is lower than that of other incandescent or halogen incandescent lamps. Their colour temperature is low, 2,800-3,000 K, so their light is warm. Their colour rendering is excellent, R a = 1a. Technical data: Their rated voltages are as a rule 6, 12 or 24 V, their rated lamp wattages are generally 10, 12, 20, 35, 50, 75 and 100 W. They have special bases. Their beam angle is usually between 8-60 o. The luminous flux generated by one lamp is: lm. Cost efficiency: Their luminous efficacy is lm/w, somewhat better than that of standard incandescent lamps, but the luminous efficacy of the lamp-transformer unit is practically the same as that of standard lamps if the loss caused by the feeding transformer is taken into account. Their life time is 2,000-5,000 hours. Their initial cost is relatively high, due partly to the transformer and partly to their complicated (lamp and mirror) design. Their initial cost per produced luminous flux is very high, -- about 15 times higher than that of simple standard incandescent lamps. Their running cost per produced luminous flux is relatively high, due to their relatively poor luminous efficacy and their relatively short life time. Operating qualities: Low voltage halogen lamps produce total light practically immediately after they are switched on (starting time is <0.1s). They provide total luminous flux without delay when they are switched on immediately after being switched off, or following a break in the voltage of the network (restarting time is <0.1 s). The operating temperature of the bulb may exceed 300 o C. Their burning position is optional. Prof. András Majoros: Artificial Lighting 19.

20 FLUORESCENT LAMPS Design and operation: The light is produced predominantly by the fluorescent powder covering the inner wall of the tube. This powder transforms the UV radiation of the gas discharge into visible light. Fluorescent lamps can only operate with the help of auxiliaries (starter, ballast, capacitor, electronic control gear, etc.). These ensure the starting and the continuity of gas discharge. The following figures show the most commonly used connections of fluorescent lamp-auxiliaries. Fluorescent lamps convert about 1/4 of their input into light. This ratio is smaller if the auxiliaries are also taken into account. Prof. András Majoros: Artificial Lighting 20.

21 The quality of light: The quality of light of fluorescent lamps may vary depending on the composition and quality of the fluorescent powder. Consequently, the spectral distribution of their light may also vary. The different quality of their light is indicated by a combination of a letter and a number, as shown in the following figure. Their colour temperature may be 2,900-6,500 K, so their light may be warm, neutral or cool. Their colour rendering varies, too, R a = 1a, 1b, 2a, 2b or 3. Technical data: The rated voltages of the tubes are between 57 and 110 V, which means that they can be operated from the 230 V of the network if the proper auxiliaries are used. The rated lamp wattage equals the input of the tube, consequently, the consumption of the auxiliary unit is higher. Depending on the sort of ballast, the input from the network exceeds that of the lamp by about - 20 % in case of normal ballast, - 10 % in case of low loss ballast and - 5 % in case of electronic ballast. The data of the rated wattages, lengths and diameters of the most commonly used fluorescent lamps are shown below: 20 W Φ 38 mm l = 590 mm 18 W Φ 26 mm l = 590 mm 14 W Φ 16 mm l = 548 mm 40 W Φ 38 mm l = 1200 mm 36 W Φ 26 mm l = 1200 mm 28 W Φ 16 mm l = 1148 mm 65 W Φ 38 mm l = 1500 mm 58 W Φ 26 mm l = 1500 mm 35 W Φ 16 mm l = 1448 mm The luminous flux generated by one lamp is: 1,000-5,400 lm. Cost efficiency: The luminous efficacy of fluorescent lamps depends on - the fluorescent powder used, - the rated wattage and - the diameter. Depending on the above parameters, their luminous efficacies are lm/w, for Φ 38 mm lm/w, for Φ 26 mm lm/w. for Φ 16 mm These values are smaller if the consumption of the necessary auxiliaries are taken into account. Their probable life time is 7,500-15,000 hours. Prof. András Majoros: Artificial Lighting 21.

22 Their initial cost is relatively high, due partly to the necessary auxiliaries and partly to their complicated design. Their initial cost per produced luminous flux is about 7 times higher than that of simple standard incandescent lamps. Their running cost per produced luminous flux is relatively low, due to their good luminous efficacy and long life time. Operating qualities: Fluorescent lamps produce total luminous flux in about 1 second after they have been switched on or after being switched off and on. Their life time mainly depends on the type of ballast used and the frequency with which they are switched on and off. The operating temperature of the tubes is o C. The burning position of the tubes is optional. Prof. András Majoros: Artificial Lighting 22.

23 COMPACT FLUORESCENT LAMPS Design and operation: Compact fluorescent lamps are usually relatively small fluorescent light sources that are or can be built together with the auxiliaries partly or completely. They operate the same way as standard fluorescent lamps. The usual types of compact fluorescent lamps - are built together with conventional or electronic ballast (fully compact), - are built together with starter and capacitor, can be plugged to the ballast or - can be plugged to the auxiliaries. Prof. András Majoros: Artificial Lighting 23.

24 The quality of light: The quality of the light of compact fluorescent lamps depends on the composition of the fluorescent powder. Consequently, the spectral distribution of their light may vary. Their colour temperature is between 2,900-6,500 K, so their light may be warm, neutral or cool. Their colour rendering is usually good, R a = 1a, 1b. Technical data: Their rated voltage depends mainly on the type. In the fully compact type it is 230, 240 V, in cases when they have to be connected to the network through auxiliaries, it is usually between 35 and 110 V. Rated lamp wattages - the input of the unit - are usually: 5, 7, 9, 11, 15, 20, 23, 24, 26, 28, 32 or 36 W. They are made either with special bases or with E 27 bases, which makes it possible to use them instead of incandescent lamps. The luminous flux generated by one lamp is: 250-2,900 lm. Cost efficiency: If they are built together with the ballast, their luminous efficacy is lm/w, if they are not, it is lm/w. Their probable life time is 8,000-10,000 hours, i.e. several hundred thousand times of switching. Their initial cost is relatively high, due to the more or less complicated design of the lamp. Their initial cost per produced luminous flux is about 3? times higher than that of simple standard incandescent lamps. Their running cost per produced luminous flux is relatively low, due to their good luminous efficacy and long life time. Prof. András Majoros: Artificial Lighting 24.

25 Operating qualities: Compact fluorescent lamps produce total luminous flux in a few seconds after they have been switched on. Total luminous flux is produced in about 1 second after they are switched off and on. Their light output depends on the environmental temperature and on their burning position. The operating temperature of the tubes is o C. The burning position of the tubes is optional. Prof. András Majoros: Artificial Lighting 25.

26 MERCURY LAMPS Design and operation: Mercury lamps belong to the group of HID (high intensity discharge) lamps. These lamps have two envelopes. The inner quartz envelope is an arc tube. The gas discharge is started by a starting electrode. The radiation generated by the electric current through mercury vapour is only partly light, its invisible part is transformed into light by the fluorescent powder on the inside surface of the outer envelope. Mercury lamps need auxiliaries (ballast or starter-transformer) for their operation. Mercury lamps convert only about 1/6 of the input into light. This ratio is smaller if the consumption of the auxiliary is taken into account. Prof. András Majoros: Artificial Lighting 26.

27 The quality of light: The quality of their light may vary depending on the fluorescent powder used. The following figure shows the spectral distribution of the light of mercury lamps. Their colour temperature is 3,350-4,000 K, so their light is warm or neutral. Their colour rendering is bad, R a = 3. Their luminance is high. Technical data: Their rated lamp voltage is V. Their rated lamp wattages are 50, 80, 125, 175, 250, 400, 700 and 1,000 W. The base of the lamps up to 125 W is usually E 27, in bigger units E 40 is used. Lamps are made with other bases, too. The luminous flux generated by one lamp is: 1,800-58,000 lm. Cost efficiency: The luminous efficacy of the lamps is lm/w, but these values are smaller if the auxiliary is taken into account. The life time of mercury lamps is 8,000-20,000 hours. Their initial cost is relatively high, due to the complicated design of the lamps and the auxiliaries needed. Their initial cost per produced luminous flux is about 13 times higher than that of simple standard incandescent lamps. Their running cost per produced luminous flux is relatively low, due to their good luminous efficacy and long life time. Operating qualities: Mercury lamps produce total luminous flux in a matter of minutes after they have been switched on. (starting time is 2-5 min.) Total luminous flux is produced in about 10 minutes after they have been switched off and on (restarting time 10 min.). The burning position of the tubes is optional. Prof. András Majoros: Artificial Lighting 27.

28 MERCURY TUNGSTEN BLENDED LAMPS Design and operation: Mercury tungsten blended lamps are mercury lamps whose ballast is a tungsten filament located between the two envelopes. The tungsten filament acts as an incandescent lamp. In this way, no auxiliary is needed, they can be used like incandescent lamps. Discharge in the quartz glass arc tube is started by a starting electrode. The radiation generated by the electric current through mercury vapour is only partly light, whose invisible part is transformed into light by the fluorescent powder on the inner surface of the outer envelope. The quality of light: The quality of the light of these lamps may vary depending on the fluorescent powder used. The spectral distribution of their light is similar to that of mercury lamps. Their colour temperature is 3,000-4,200 K, so their light is warm or neutral. Their colour rendering is bad, R a = 3. Their luminance is high. Technical data: Their rated lamp voltage is V. Their rated lamp wattages are generally 160, 250 and 500 W. The bases of lamps of 160 W are usually E 27, those of larger units are E 40. Lamps are made with other bases, too. The luminous flux generated by one lamp is: 3,000-14,000 lm. Prof. András Majoros: Artificial Lighting 28.

29 Cost efficiency: The luminous efficacy of these lamps is lm/w. The life time of mercury tungsten blended lamps is 8,000-10,000 hours. Their initial cost is relatively high, due to the complicated design of the lamp and the auxiliary needed. Their initial cost per produced luminous flux is about 11 times higher than that of simple standard incandescent lamps. Their running cost per produced luminous flux is better than that of incandescent lamps, but worse than that of other discharge lamps, due to their relatively poor luminous efficacy and long life time. Operating qualities: Mercury tungsten blended lamps produce a considerable part of the total luminous flux in 0.1 sec after they have been switched on, but they reach total luminous flux only a few minutes (in 5 min.) after switching on. Total luminous flux is produced about 10 minutes after they are switched off and on (restarting time 10 min.). The burning position of the lamps can be either optional or vertical with defined deviation. METAL HALIDE LAMPS Design and operation: Metal halide lamps are HID lamps, too. They have two envelopes. The inner quartz arc tube contains other metal halides in addition to mercury. Light is generated in the arc tube either with the help of an auxiliary electrode or with the help of a starting impulse. The outer envelope may or may not have a fluorescent powder coating. Prof. András Majoros: Artificial Lighting 29.

30 Metal halide lamps convert only about 1/4 of the input into light. This ratio is smaller if the consumption of the auxiliary is taken into account. Prof. András Majoros: Artificial Lighting 30.

31 The quality of light: Their quality of light depends on the metal halides used in the arc tube. Their spectral distribution is shown in the next figure. Their colour temperature is 3,000-6,000K, so their light may be warm, neutral or cool. Their colour rendering is usually good, R a = 1a, 1b or 2a. Technical data: Their rated lamp voltage is V. Their rated lamp wattages are 35, 75, 150, 250, 400, 1,000, 2,000 and 3,500 W. The base of the lamps are either Edison type or a special type at both ends. Metal halide lamps are produced as reflector lamps, too. The luminous flux generated by one lamp is: 2, ,000 lm. Cost efficiency: The luminous efficacy of the lamps is lm/w, these values are smaller if the auxiliary is taken into account. The life time of mercury lamps is hours. Their initial cost is relatively high, due to the complicated construction of the lamp and the auxiliary needed. Their initial cost per produced luminous flux is about 10 times higher than that of simple standard incandescent lamps. Their running cost per produced luminous flux is relatively low, due to their good luminous efficacy and more or relatively long life time. Operating qualities: Metal halide lamps produce total luminous flux in a matter of minutes after switching on (starting time is about 5 min.). Total luminous flux is produced in about 10 minutes after they are switched off and on (restarting time 10 min.). In some special types with extra built in electrodes restarting time is only a few seconds. The burning position of the tubes is usually defined. Prof. András Majoros: Artificial Lighting 31.

32 HIGH PRESSURE SODIUM LAMPS Design and operation: High pressure sodium lamps belong to the group of HID lamps. They have two envelopes. Light is produced by the electric current through high pressure sodium vapour in the arc tube, which is made of aluminum-oxide. Light is usually generated with the help of a high voltage impulse. There are, however, some types that do not require a starter. High pressure sodium lamps are made either with transparent or translucent outer bulbs. Prof. András Majoros: Artificial Lighting 32.

33 High pressure sodium lamps convert only about 1/3 of the input into light. This ratio is smaller if the consumption of the auxiliary is taken into account. The quality of light: The quality of light of sodium lamps is not very good. Its spectral distribution is shown in the following figure. The colour temperature of these lamps is 2,000-2,200 K, so their light is warm. Their colour rendering is bad, R a = 3 or 4. Technical data: Their rated lamp voltage is about V. Their rated lamp wattages are usually 50, 70, 100, 150, 250, 400, 600, 1,000, 2,000 and 3,500 W. The base of the lamps are Edison type or a special type at both ends. All of them need auxiliaries for their operation. The luminous flux generated by one lamp is: 2, ,000 lm. Cost efficiency: The luminous efficacy of the lamps is lm/w, these values are smaller if the auxiliary is taken into account. The life time of mercury lamps is 10,000-28,000 hours. Their initial cost is relatively high, due to the complicated design of the lamp and the auxiliary needed. Their initial cost per produced luminous flux is about 13 times higher than that of simple standard incandescent lamps. Their running cost per produced luminous flux is very low, due to their very good luminous efficacy and very long life time. Operating qualities: High pressure sodium lamps produce total luminous flux in 6-15 minutes after being switched on. Total luminous flux is produced in about 1-5 minutes after they are switched off and on. The burning position of the tubes is optional. Prof. András Majoros: Artificial Lighting 33.

34 THE ROUTE OF LIGHT FROM THE LIGHT SOURCE TO THE REFERENCE PLANE In artificial lighting, the interior is illuminated by the luminous flux of a lamp. The light of a light source reaches the surfaces of the room through the luminair. The surfaces of the interior more or less reflect this light, and they illuminate each other in the process. Each instance of reflection reduces the amount of available light, so finally it is absorbed. At a given moment, a given surface is illuminated at the same time both by light directly radiated from the lamp and by light indirectly reflected from the surfaces. It follows from what has been said above that every element of surface of a room is practically illuminated by a hemisphere: the hemisphere that is "seen" by the element. So a given surface of the interior is illuminated by the luminaires and surfaces it sees, in other words, the surface is exposed to the luminous flux of a hemisphere, to light coming from different directions and at different intensities. There are different ways by which the light of a light source can reach a given surface of the room. These ways as well as the quantity and quality of the utilized luminous flux of the light source vary depending on the luminaire and the surfaces. If we want to take into account all the above, and we want to plan the illumination of the interior, we must clarify the details of this chain of effects. That is why it is advisable to follow the route of light from the light source to the reference plane. The light output of a light source is characterized quantitatively by Φ o luminous flux, and qualitatively by T colour temperature and R a colour rendering. Prof. András Majoros: Artificial Lighting 34.

35 Light sources are always built into luminaires. Luminaires serve several technical and lighting functions. Their most important technical functions are: - to fix the lamp and to supply it with energy, - to protect the lamp from the environment and the environment from the lamp. Their lighting functions as follows: The lamp radiates only part of the luminous flux into the room, and it absorbs the rest. The effectiveness of a luminaire from this point of view is called the efficiency of the luminaire. The efficiency of a luminaire is the ratio of the luminous flux emitted by the luminaire Φ L and the luminous flux generated by the lamp Φ o. Its symbol is η L, its unit is [%]. From the point of view of lighting, the most important function of a luminaire is to distribute light in the room in the required stereoscopic manner. Luminaires can distribute and direct the light of lamp into space in different ways. Light distribution, 3D distribution of light emitted from a surface can be described by luminous intensity. Prof. András Majoros: Artificial Lighting 35.

36 Luminous intensity is the luminous flux per unit solid angle in question, its symbol is I, its unit is candela, [cd]. The distribution of a luminaire's light is characterized by so-called candle-power curves. A candle-power curve shows I luminous intensity in different directions on a plane laid through the luminair. As luminous intensity is a vector, each point of the candle-power curve represents the value of the luminous intensity vector pointing at the direction indicated by the point. Prof. András Majoros: Artificial Lighting 36.

37 Luminaires are classified according to their manner of lighting based on their light distribution: the ratio of luminous flux radiated up and down an endless horizontal plane lain through the luminaire. Prof. András Majoros: Artificial Lighting 37.

38 There is considerable difference between the possible utilization of the two parts of the luminous flux, since the part radiated down by the luminaire can, theoretically, reach the reference plane -in an infinitely large room-, but then the part of the luminous flux radiated up to an infinite plane can reach the reference plane only after one or more reflections, therefore only a fraction can be utilized. The ratio of illumination of a certain surface of the room is determined by the location of the luminaires in the interior and by their light distribution. Luminaires can affect the utilization of the light of a lamp in yet another way. If the transparent and/or reflecting part of the luminaire is coloured, the luminaire modifies the quality of the light of the light source. The transparent or reflecting parts of luminaires that are used for general lighting are not coloured, so they do not change the light of the light source. Prof. András Majoros: Artificial Lighting 38.

39 The light emitted from the luminaire and illuminating the surfaces of the interior, can be described by illuminance. Illuminance is the luminous flux collected by unit of surface. Its symbol is E, its unit is lux [lx]. Illuminance is an effect the surface is exposed to. Illuminance of a surface depends on the direction of the incident light. Luminous flux produces the largest illuminance on a surface that is at right angle to it. Light will not illuminate a surface that it is parallel to. It follows from the above that a luminaire close to a surface can only illuminate effectively the part of the surface closest to it. Illuminances coming simultaneously from different sources add up. Prof. András Majoros: Artificial Lighting 39.

40 Surfaces change the characteristics of light in the following way: - Each surface reflects only part of the luminous flux, and absorbs the rest, - Surfaces change the direction of light - more or less dispersing it, - Coloured surfaces change the quality of light. The Φ o luminous flux reaching a surface is - partly reflected (Φ ρ ), - partly absorbed (Φ α ) and - partly transmitted (Φ τ ), if the surface is transparent. The ratio of these parts are ρ reflection factor α absorption factor τ transmission factor The ρ reflected part of the luminous flux is the part that is visually perceptible. It is this part that can be used to illuminate the surfaces of a room. Surfaces of different quality reflect and disperse light in different ways. Surfaces can be divided into three main classes as shown in the following figure. The dispersion of reflected light can be characterized with the distribution of luminous intensity. Prof. András Majoros: Artificial Lighting 40.

41 The figure illustrates the following: - mat surfaces reflect light evenly irrespective of the direction of the incident light, - mirrors and shiny surfaces reflect light highly unevenly and depending on the direction of the incident light. In mirrors, the illuminated point can only be seen from direction "B". In shiny surfaces, the illuminated point is darker from direction "A" than "B". In mat surfaces, the illuminated point is equally bright viewed from every direction. The quality i.e. the spectral distribution of Φ o (λ), the light illuminating the surface, and of Φ ρ (λ), the light reflected from the surface, may be the same or more or less different depending on the ρ(λ) reflection function of the reflecting surfaces, according to the following equation Φ ρ (λ) = ρ(λ) * Φ o (λ) With white, grey and black surfaces, the reflected and the illuminating light are nearly identical in quality. Coloured surfaces mainly absorb their respective colours, consequently the reflected and the incident lights differ greatly in quality. A reference plane is illuminated by the luminous flux coming directly from the luminaires, and indirectly by the luminous flux coming from some of the room's surfaces. A point of the reference plane is illuminated by all the points of the room which it "sees", i.e. every surface element is illuminated by a hemisphere, whose elements can be luminaires or surfaces illuminated and reflecting light to various degrees. The reference or working plane is the part of the room the visual task refers to. Normally, it is a horizontal plane 0.85m above the floor, or in communicating areas it is the floor. What the spectator sees is that parts of his or her field of view varies in brightness and colour. How is a surface seen? An observer viewing a surface from a given direction perceives an I* luminous intensity coming from an A* virtual size of surface. It is this that makes a surface look bright to some degree. What is seen is the luminance of the surface. Prof. András Majoros: Artificial Lighting 41.

42 Luminance is the luminous intensity of an element of surface seen as a unit. Its symbol is L its unit is cd/m 2. It follows from the above that - the luminance of mirrors and shiny surfaces varies with the direction of viewing, - the luminance of mat surfaces are constant independent of the direction of viewing. From the point of view of the visual environment, using mat surfaces is more advantageous. Prof. András Majoros: Artificial Lighting 42.

43 THE REQUIREMENTS OF LIGHTING Theoretically, lighting must meet the following requirements : 1. Lighting has to ensure the accurate and speedy vision that is necessary for the given task. 2. For accurate vision, the details of the object as well as the colour and spatial location of the details have to be seen as clearly as the task requires. 3. Visual discomfort caused by lighting has to be limited to an acceptable degree. 4. While meeting the requirements of the visual task, lighting has to be cost effective. The above theoretical requirements can be met in practice if the requirements of lighting are quantified. For accurate vision it is necessary to perceive the details of the task to an appropriate degree. The exact perception of a detail of the environment means being able to differentiate between the details, their luminances and colours to the required degree as well as perceiving their spatial location. The requirement of accurate vision can be met with definable values of the following characteristics of lighting: Illuminance on the reference plane, Colour rendering, and Shadow effect. Visual discomfort can be limited with definable values of the following characteristics of lighting: The colour of light, Glare, and The ratio of luminances. Lighting serves the visual task effectively: if the installation and operation of the artificial lighting system is cost effective, and if the process of visual perception is efficient. Requirements vary from case to case, i.e. the requirements of a given activity is one of a great number of possible combinations. ILLUMINANCE ON THE REFERENCE PLANE Every visual task has a reference plane. As most tasks have to do with work, the reference plane is sometimes called the working plane, too. Unless otherwise specified, the reference plane is generally a horizontal plane 0.85 m above the floor in working areas, or the floor in circulation areas. Every visual task requires a certain degree of visual accuracy and contrast sensitivity, i.e. a certain degree of visual ability. As visual ability depends on the average luminance of the field of view, and the luminances of the elements of the field of view depend on the ρ quality of the surface and on E illuminance of the surface according to the L = ρ * E equation, the average luminance of the field of view can be changed by changing the illuminance if the surfaces of the interior (ρ ) are constant. L E In this way, the requirement of the average luminance of the field of view can be defined as a requirement of illuminance. Prof. András Majoros: Artificial Lighting 43.

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