Основы светотехники на английском языке, страница 2

A15.1 Important Measuring Hints.................................................................................................. A15.2 Measuring Equipment and Generators Used......................................................................... A15.3 Comparison of all Lamps Used in this Manual....................................................................... A2SolutionsFoils:ILLUMINATION BOARD (Type 2102)SPECIAL LAMP BOARD (Type 2103)HALOGEN BOARD (Type 2104)Fundamental Principles of Lighting EngineeringIntroduction11Fundamental Principles of LightingEngineeringLighting engineering is a relatively new technological field which became possible by the invention of theelectric lamp by Thomas Edison in 1879.However, specific planning and application of lighting engineering has only been performed for the lastfew decades.

Optimum working and living conditions can be achieved by the right combination and selection of lamps and light sources.1.1IntroductionSome of the basic theoretical principles need to be studied before beginning with practical lighting engineering.1.1.1Electromagnetic wavesLight is an electromagnetic radiation which only differs from other electromagnetic waves in its wavelengthand frequency.The sun’s radiation which reaches us contains a large number of waves of different wavelengths. Only asmall proportion of these reach the earth. In turn, light constitutes only a small part of the waves whichreach the earth.

We can see the direct effect of the light and analyse it with the help of a prism (figure1.1.1).Figure 1.1.1 Spectrum of electromagnetic wavesThe division of light through a prism can also be observed as a natural phenomenon in the form of a rainbow.

Raindrops act as a prism and divide the light according to wavelength.The visible spectrum of light from the colour violet to red has a wavelength of 380 nm to 780 nm. 1 nm-9(10 m) is the millionth part of a millimetre.The wave characteristic of light is shown by the wavelength λ (lambda) and therefore with a certain fre6quency f. Both variables are connected with the velocity of light c which is 300 x 10 m/s in a vacuum.λ=cf21.1.2Fundamental Principles of Lighting EngineeringIntroductionThe human eyeThe human eye (figure 1.1.2.1) is often compared with a camera as a strong simplification.The „lens“ is formed by the cornea, the vitreoushumour and the lens. The „aperture“ is the irisand the light-sensitive film the retina.

The human eye does better in this comparison thanthe very best of cameras.The lens adjusts very quickly and unconsciously to produce a sharp image on the retina. The aperture opening, recognisable by thesize of the pupil also adjusts automatically tofluctuating light conditions.

The pupil retracts tolet less light into the eye at a great brightnessand dilates at low brightness.Figure 1.1.2.1 The structure of the human eyea) cornea, b) iris, c) lens, d) vitreous humour, e) retina,f) fovea centralis, g) blind spot, h) optic nerveThe retina carries photoreceptors with different functions. They are divided based on their shape into cones and rods (figure 1.1.2.2).7 million cones on the retina serve to be able to seeduring the daytime and to recognise colours. 130 million rods serve to be able to see with small light. Nocolours are recognisable with the rods.Figure 1.1.2.2 Rods and conesThe cones react especially to the yellow-green part of the light spectrumand have their maximum sensitivity at555 nm.

The non-colour-sensitive rodsare most sensitive at a wavelength of507 nm.Figure 1.1.2.3 shows the relative spectral brightness sensitivity dependent onthe wavelength.Figure 1.1.2.3 Brightness sensitivityFundamental Principles of Lighting EngineeringBasic Lighting Engineering Variables31.2 Basic Lighting Engineering Variables1.2.1 Light sourcesLight sources can be divided as follows:Primary light sourcesPrimary light sources convert energy directly into light (e. g. the sun or electric lamps).Secondary light sourcesSecondary light sources pass on radiated light by reflection or transmission (light transmitting capacity).They may change the spectrum of light.

However, it contains only radiation which is fed externally. Lightswith a built-in lamp are an example of such secondary light sources.Temperature radiatorsAll objects radiate energy as a result of their temperature. The greater the temperature of a solid, themore energy it radiates. At a temperature of 0 K (-273 °C, absolute zero point), the radiated energy iszero.The temperature is usually specified in Kelvin (K). The radiation becomes visible in the dark from a temperature of 800 K (523 °C). However, the intensity of the radiation depends on the surface of the solid.Dark, matt primary light sources radiate better than solids with a bright, glossy surface. Heat sinks in electronics exploit this characteristic especially .Black solidsBlack solids are often referred to as Planckian radiators.

They absorb all radiation from all wave ranges.When heated, it becomes black radiator and emit a defined radiation.SunlightSunlight is a temperature radiator with about 5800 K. Approx. 1000 W/m² radiation power can be measured on the earth’s surface at a vertical radiation angle. This is used for producing electricity and heat bymeans of photovoltaics or sun collectors.Cloud and sky lightThe earth’s atmosphere is a secondary light source. It contains the light of the sun which is dispersed byair molecules.

Since shorter wavelengths are dispersed more, the sky appears blue. The longer wave lightis dispersed more by clouds or water droplets so that clouds appear white.DaylightDaylight is a mixture of sunlight, sky light and cloud light which is continually changing its spectral composition due to influences of the time of the day and the weather.LuminescenceAll light radiation which does not obey temperature radiation is referred to as luminescence. It includes allprocesses which have to do with gas discharge, fluorescence and phosphorescence phenomena.LaserThe laser is basically a primary light source which can emit a closely bundled, polarised, monochromaticlight.1.2.2Standard light typesStandard light types are light types specified internationally according to the CIE.

They serve for technicalevaluation and dimensioning of light sources and materials.CIE defines the following light types:Standard light type ALight of a black solid with a temperature of 2856 K and a wavelength of 300 nm to 830 nm. This light isgenerated by a filament lamp with a colour temperature of 2856 K with very good approximation.4Fundamental Principles of Lighting EngineeringBasic Lighting Engineering VariablesStandard light type BThis light corresponds to sunlight with a colour temperature of 4874 K. It can be generated by a filamentlamp with an additional filter.Standard light type CThis light has a colour temperature of 6744 K and corresponds to average daylight from a combination ofsunlight and sky light. It can be generated by a filament lamp with filter.Standard light type D65This light corresponds to a daylight of 6504 K. Unlike the standard light types A and B, it contains a UVpart corresponding to daylight.

This light is used for evaluating colours, colour trueness, yellowing problems etc. However, it is very difficult to produce this light because there is no defined radiator with this colour temperature.1.2.3Spectral brightness sensitivityLight is the radiation which is „visible“ to the human eye. UV and infrared radiation (heat radiation) are invisible although the eye perceives them and can be damaged by them.The spectral brightness sensitivity is very important.

The brightness sensitivity of the human eye dependsnot only on the radiation power but also on the wavelength of the light. The CIE has defined the evaluationfunction for a normal sighted person as the spectral brightness sensitivity function with a V(λ) curve.In daylight vision the V(λ) curve at whichcolours are clearly perceived (photoptic vision) applies. The maximum brightnesssensitivity is at a wavelength of about555 nm (yellow-green).In night-time vision, the V’(λ) curve at whichcolours are unclearly visible (scotopic vision)applies.

The maximum brightness sensitivityis at about 507 nm (blue-green).This effect is used for example in xenonheadlamps of automobiles. This light contains less red parts and more blue parts sothat the brightness sensitivity is greater atthe same light power.Figure 1.2.3 shows the spectral brightnesssensitivity V(λ) of the human eye accordingto CIE as a function of the wavelength λ.1.2.4blue1.00.9V (λ) 0.8V´(λ) 0.7night0.6V´(λ)0.50.40.30.20.10400 450greenyellow orangereddayV (λ)600500 550555650 700λ / nm750Figure 1.2.3 Spectral brightness sensitivity curves fordaytime and night-time visionLight current ΦPower is usually given in Watts (W) in energy technology. However, since the brightness sensitivity of thehuman eye behaves according to the V(λ) curve and depends on the wavelength of the light, the radiationpower in lighting engineering says very little.For this reason, the light current Φ with the unit Lumen (lm) was introduced in lighting engineering.The light current therefore represents the “light power“ of a light source (figure 1.2.4).The light power and the light current are connected with the radiation equivalent K (lm/W).5Fundamental Principles of Lighting EngineeringBasic Lighting Engineering VariablesFor monochromatic light with a wavelength of 555 nm (max.

sensitivity of the human eye) the following equation applies for daytime vision:K max = 673 lm / WA monochromatic light source with a wavelength of 555 nm and alight current of Φ = 673 lm therefore has a light power of 1 W.Examples of light currents of different light sources:•••Filament lamp 230 V / 100 W:Fluorescent lamp 230 V / 36 W:High-pressure sodium vapour lamp230 V / 100 W:1380 lm3450 lm10 000 lmFigure 1.2.4 Light power1.2.5Quantity of light QThe quantity of light Q is shown in figure 1.2.5.

It is the product of the light current Φ and time t.ΦQ = Φ ⋅tQThe quantity of light is important for calculating lighting costsand for problems in connection with the influencing of materials (e. g. bleaching, etc.).Example:For a 100-W filament lamp with Φ = 1380 lm and an averagelife of t = 1000 hours (h), the quantity of light is:tFigure 1.2.5Q = Φ ⋅ t = 1380 lm ⋅ 1000 h = 1.38 ⋅ 10 6 lm = 1.38 Mlmh1.2.6Solid angle ΩThe light propagates evenly to all sides of theroom. Imagine a light source at the centre ofa hollow spherical solid which radiates ontothe whole surface of the sphere.If, however, you observe only a certain radiation angle (solid angle) only a part of the lightsource’s light current falls on it (figure 1.2.6).punctiformlight sourceAThe quotient Ω with the unit steradiant (sr) isreferred to as the solid angle.iradFigure 1.2.6 Solid angleus r6Fundamental Principles of Lighting EngineeringBasic Lighting Engineering VariablesΩ=Ar2The solid angle Ω is the value given by the size of the radiated area A and the square of the distance r .The full solid angle of a spherical surface is therefore:Ω=A 4π ⋅ r 2== 4π ⋅ sr = 12.56 srr2r2Accordingly, the solid angle of a hemisphere is 6.28 sr.1.2.7Luminous intensity IOriginally the Hefner candle (HC) invented by F.