Основы светотехники на английском языке (989259), страница 3
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Hefner in 1884 was used as the luminous intensity standard. The luminous intensity of the Hefner candle corresponds approximately to a composite candle with adiameter of 2 cm with a flame height of 5 cm. Since 1941, the unit Candela (lat. candle) has been used asa basic unit for the luminous intensity. The Candela unit as a basic unit of lighting engineering is definedas one of the seven basic units in the SI system.The unit of luminous intensity is 1 Candela (cd).1 cd ≈ 1.16 HKThe luminous intensity I evaluates the light radiated in a certain direction, whereby 1 Candela corresponds12to a radiation power of 1/683 Watt at a monochromatic radiation of the frequency of 540 x 10 Hz.The luminous intensity I can be calculated using the solid angle Ω and the light current Φ.I=ΦΩExample:If a filament lamp (230 V / 100 W) is placed at the centre of a sphere, it emits light evenly in all directions.The luminous intensity is therefore:I=Φ 1380 lm== 109.87 cdΩ 12.56 sr1.2.8Illuminance EIf a light current Φ hits an area A vertically (figure 1.2.8), this area is more or lessilluminated according to its size.
The illuminance therefore corresponds to a certain degree to the „power density“. It is calculated with the formula:E=ΦAThe illuminance has the unit Lux (lx).The illuminance E is the quantity of light which actually hits an area. It is usedabove all as a dimensioning variable for interior lighting. However, it should benoted that the illuminance says nothing about the brightness impression receivedby the eye.Figure 1.2.87Fundamental Principles of Lighting EngineeringBasic Lighting Engineering VariablesExamples of illuminance:•••Cloudless summer day:Dull summer day:Office lighting:1.2.9up to 100 000 lx20 000 lx500 lx•••Dull winter day:Full moon night:Starry night:400 lx0.3 lx0.01 lxLighting density LThe lighting density L in cd/m² is a measure of the brightness impression which the eye has of an area A (figure 1.2.9.1).
It is the only visiblevariable in lighting engineering. The basic relationship is:L=IAL=IAIf the lighting density (brightness) is toogreat, „glare“ occurs which leads to eyefatigue and impairs vision (figure1.2.9.2).Daily examples of lighting density:•Figure 1.2.9.1••••Figure 1.2.9.2 GlareOpening a window at midday:light cloudcloudyOpal filament lamp (100 W):Fluorescent lamp:White paper at 500 lx:Environmentally friendly paper at 500 lx:5000 ...
50 000 cd/m²1000 ... 3000 cd/m²60 000 cd/m²5000 ... 15 000 cd/m²130 ... 150 cd/m²90 ... 100 cd/m²1.2.10 Luminous intensity distribution curve LVKMost lights do not radiate evenly in all directions. Certain areas are illuminated more strongly dependingon the light deflection of the light. This spatial distribution is specified with the help of the luminous intensity distribution curve LVK whereby the polar co-ordinates system is usually used. Figure 1.2.10 showsvarious luminous intensity distribution curves (A to H).Figure 1.2.10 luminous intensity distribution curves8Fundamental Principles of Lighting EngineeringBasic Lighting Engineering Variables1.2.11 Contrast reproduction factor CRFAn object can only be perceived if it can be distinguished from its background by means of its colour orcontrast.
The lighting density of the object should differ from the lighting density of the environment so thatcomfortable vision is possible. The lighting density contrast is therefore a measure of the perceptibility anddepends on the local illumination situation and can be defined by the following relationship:C=(LU− LD )LUC = The lighting density contrastLU = The lighting density of the environmentLD = The lighting density of the objectThe photometric contrast K is defined in the standard DIN 66 234 as:K=LULDThe contrast reproduction factor CRF is defined as a light-technical quality characteristic for internal illumination as follows:CRF =CC0with C0 = 0.91 (fixed reference contrast)A three-step division is used for assessment of thecontrast reproduction factor which is used above allfor activities such as reading, writing and drawingwhere small details of vision are important for example in offices, classrooms, production rooms etc.StepRequirementCRFmin1high≥ 0.952medium≥ 0.73low≥ 0.51.2.12 Luminous efficiency ηThe luminous efficiency η is a measure of the effectivity of a lamp.
The unit is lumen per Watt (lm/W).η=ΦPel .Pel. = electrical power in WThe luminous efficiency can be referred either to the power consumption of the lamp alone or – especiallyin fluorescent lamps – to the power consumed by the system (incl. choke, etc.). In this case we refer tothe system luminous efficiency.
There is a theoretical upper limit to the luminous efficiency of 673 lm/W.Examples of luminous efficiency:•••••••Filament lamps:Halogen filament lamps:Fluorescent lamps:High-pressure mercury vapour lamps:High-pressure sodium vapour lamps:Halogen high-pressure lamps:Low-pressure sodium vapour lamps:10 ... 15 lm/W14 ... 25 lm/W58 ... 100 lm/W32 ... 58 lm/W40 ... 150 lm/W54 ... 120 lm/W150 ... 200 lm/WFundamental Principles of Lighting EngineeringBasic Lighting Engineering Variables91.2.13 Coefficient of utilization KBThe coefficient of utilization KB is determined by various criteria. The contamination of walls and ceilingsas well as the ageing of the light source play an important role in the illumination strength in addition to thelamp design and nature of the room.
The coefficient of utilization value is always specified by the lampmanufacturer.Arithmetic calculation of the light current is therefore also dependent on the coefficient of utilization. This isusually included as a factor in the calculation.E) KBABelow, the coefficient of utilization for four different lamp systems arranged in the same room is specified:xxxxFree radiating lamp:Reflector grid lamp:Indirect lamp:direct/indirect:KB = 0.67KB = 0.68KB = 0.38KB = 0.571.2.14 Dimensioning of illuminationIn order to achieve a specified illumination E at the useful level in a room, a minimum number of lamps nis required.
This is calculated with the formula:E) KBA 1.251.25 = Planning factor due to ageing of the systemn)) LP) = necessary total light current)LP = lamp light current (new value) according to manufacturer specificationsExample:An office, 11 m long, 4 m wide and 3 m high, with a bright ceiling and medium bright walls is to have alargely direct general illumination. Universal white fluorescent lamps with a light current of )LP = 3450 lmare chosen as light sources for the illumination.
High demands are made on illumination for office work(500 lx). The manufacturer specifies the coefficient of utilization at KB = 0.6.A11 m 4 mE) K BAo)n 1.25EAK B 1.25)) LP44 m 2500 lx 44 m 20.6 1.2529333.33 lm3450 lm29333.33 lm8 .5Nine fluorescent lamps are therefore required for good illumination the office.10Fundamental Principles of Lighting EngineeringBasic Lighting Engineering Variables1.2.15 Colour temperature TFThe light colour of a lamp is determined by the colour temperature TF . A black solid is used for comparison which adopts specific colours at certain temperatures. The colour can therefore be defined withthe temperature specification in Kelvin (K) of theblack solid.If the light colour matches the colour of the blacksolid, it is assigned the temperature in K.twdaylight white> 5000 Knwneutral white3300 K ...
5000 Kwwwarm white< 3300 KFor general illumination purposes, the DIN 5035standard divides the colour temperature into threegroups as shown in the table above.Figure 1.2.15 shows examples for colour temperatures of different lamps.Figure 1.2.15 Colour temperatures1.2.16 Colour reproduction index RaThe colour reproduction index Ra serves as a measure for the description of the colour reproduction capability of lamps. A natural impression is only possible if the light used contains the whole spectrum.
Inpractice, the colour reproduction indices are divided into six stages according to CIE and DIN (table1.2.16).Colour reproduction propertyColour reproduction stageColour reproduction index Ra1A≥ 901BLamp examplesApplication examplesFilament lamps „de-Luxe“,fluorescent lampsGraphic industry, museums, salesrooms for textiles80 ... 89Triple-band fluorescentlampsRooms with normal colourvision purposes2A70 ... 79Fluorescent lamps: e. g.Osram 10, 25; Philips 25Rooms with normal colourvision purposes2B60 ... 69Halogen metal vapourlampssatisfactory340 ...
59High-pressure mercury vapour lampsWork in which colour vision is unimportantunsatisfactory420 ... 39High-pressure sodium vapour lamps and low-lampsStreet lightingvery goodgoodTable 1.2.16 Colour reproduction indices according to CIE and DINFundamental Principles of Lighting EngineeringFeatures of Good Light1.3Features of Good Light1.3.1Factors for good light11Figure 1.3.1 shows what factors are responsible for „good light“.room climateillumination levellight colour,colour reproductiongoodlightshadowbrightness distributionglare limltinglight directionFigure 1.3.1 Factors for „good light“1.3.2Conditioning and room climateConditioning of a room has the aim of balancing all the influences on a person in the room.
Neither thesum of these influences nor individual influential variables should affect the well-being and thus the willingness and capability of the person to perform.The interaction of lighting, room colours, climate technology and acoustics is responsible for the room climate, the importance of which is undisputed today.The high demands on lighting, room design, air and acoustic technology in classrooms and open-plan offices demand planning co-ordination. Other reasons for common planning are the large space required forlighting systems, air-conditioning systems and sound-insulation for which only the ceiling is usually available, especially in large rooms.For the above mentioned reasons, air-conditioning equipment is combined with lighting systems.
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