Основы светотехники на английском языке (989259), страница 4
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This hasgreat advantages: Relief of an air-conditioning system by dissipation of lamp and light heat, increased efficiency of fluorescent lamps, reduction in disturbing heat radiation, etc.1.3.3Illumination levelThe illumination level is basically determined by the illuminance E. However, it is also influenced by the reflection properties of the ceiling and walls, furniture and floor. Vision is directly dependent on the illumination level. The illumination level of a room is defined by the rated illuminance.The rated illuminance En / lx, planned for a certain activity determines the type of sight task and shouldapply as an average value in the whole room or an area of the room.
It is usually determined for a horizontal reference level of 0.85 m above the floor. In the planning, the rated illuminance should be multiplied by12Fundamental Principles of Lighting EngineeringFeatures of Good Lightfactor 1.25 under normal ageing conditions because the illuminance diminishes with progressive ageing ofthe lamps and by dust on lamps, lighting systems and reflecting room surfaces.Figure 1.3.3 shows the course of the average illuminance and illuminance at the most unfavourable workplace which cannot be less than 50% of the rated illuminance.illuminanceactual new valueplanning value1.251.0rated value0.8minimum value0.50unfavourableworkplacestartingtime tserviceserviceFigure 1.3.3 IlluminanceTables 1.3.3.1 and 1.3.3.2 show the minimum requirements for the illumination of classrooms.Fluorescent lampsType of room or activityEn / lxLightcolourQuality classStage of colof the limitingour reproducof direct glaretion propertiesPlanning notesPre-school rooms3 00ww, nw21*)Classrooms if the restrictions in thenext line do not apply300ww, nw21*)At the workplaces at least0.8 x EnClassrooms with a daylight quotientD < 1% at the most unfavourableworkplace and for mainly eveninguse or especially for adult education500ww, nw21*)The illuminance requiredfor other activities can beachieved by switching partsof the lighting system.High degrees of reflection: ceiling at least 0.7;walls/partition walls atleast 0.5750ww, nw21*)Medium degrees of reflection1000ww, nw21*)LargeclassroomsTable 1.3.3.1 General classroomsAdditionallightingmust beprovided forthe mainblackboardand/ordemonstration desk.Fundamental Principles of Lighting EngineeringFeatures of Good Light13Fluorescent lampsType of room or activityEn / lxLightcolourStage of colour reproduction propertiesQuality classof limiting ofdirect glareTraining kitchens500ww, nw22Works500ww, nw21Handicraft, sewing and typingrooms500ww, nw21Drawing, painting500ww, nw11Physics, Chemistry and Biology500ww, nw21*)Laboratories, practical rooms forexperiments500ww, nw21Technical drawing750ww, nw21Planning notesEn related to the centrepoint of the drawing boardat a height of 1.2 m ; drawing board tilted 75° to thehorizontal.
Attention mustbe paid to luminous intensity distributionAdditionallightingmust beprovided forthe mainblackboardand/ordemonstration desk.Table 1.3.3.2 Special classrooms*) The next highest rated illuminance is decisive for the quality class of the limiting of direct glare.1.3.4Harmonious brightness distributionThe illuminance in the room says nothing yet about a harmonic, balanced distribution of lighting densitiesof different areas.The careful adaptation of the degrees of reflection of all surfaces in the room is the prerequisite for a harmonious lighting densities distribution.Different degrees of reflection cause contrasts betweenthe ceiling, the walls, furnishings, curtains and floorings.The brightness distribution in the room can have organisational functions by emphasising, combining or isolatingareas of the room.The best vision conditions exist when the lighting densities contrasts between the object of vision (e. g.
writingpaper) and larger areas of the environment are kept incertain limits. The ratio of lighting densities in the field ofvision should not be greater than 3:1 and not less than1:3 (figure 1.3.4).A harmonious brightness distribution and the necessaryillumination level produce the conditions for physical andmental well-being.Figure 1.3.4 Distribution of luminances141.3.5Fundamental Principles of Lighting EngineeringFeatures of Good LightLimiting of glareGlare reduces power of vision (physiological glare). Afterlonger stays in the room glare will cause discomfort andfatigue.
It reduces well-being and diminishes the workingperformance (psychological glare). Sensitivity to glare increases with age.Sensitivity to glare depends mainly on the lighting densitiesand sizes of the visible luminous areas (indirect glare), alllights in the field of vision, their position in the field of vision (direct glare) and the luminance of the environment orbackground.Figure 1.3.5 shows that the man at the desk is disturbedby direct glare. The glare occurs at an angle of visiongreater than 45°. The angle of vision depends on the roomdepth a and the height of the lights above eye level hs. Theglare is increased further by the unsuitable arrangement oflights (naked fluorescent lamps) transversely to the observer.
This can be avoided by good planning of the lighting system.1.3.6Figure 1.3.5 GlareLight direction and shadowLight direction and shadow influence the optical information about the things that we see. The light distribution of the lights and their arrangement in the room determine the direction of light. The direction of lightinfluences the forming of shadows and must therefore be adapted to the tasks of vision.Shadows can be placed purposely to accentuate room areas and danger zones.
They are used for effective representation of goods, safe handling of tools and no-risk operation of machines. Checking of surfaces is simplified by directed incident light.The light of a single lamp generally causes solid and hard shadows and can cause distorted light of an illuminated object (figure 1.3.6.1).Additional lights from other directions can brighten the shadows and improve the visibility of an object (figure 1.3.6.2). Band arrangement of lights form soft shadows (figure 1.3.6.3).Figure 1.3.6.1Figure 1.3.6.2Figure 1.3.6.3Fundamental Principles of Lighting EngineeringLight Sources1.4Light Sources1.4.1General15Light sources can usually be divided into two classes:Temperature radiatorsThe temperature radiators include filament lamps which belong to the oldest electrical lamps.
Whereas acarbon filament lamp of 1882 had a light yield of three lumen per Watt (3 lm/W), modern filament lampshave a luminous efficiency of about 12 to 30 lm/W.Filament lamps whose glass bulbs have a light reflecting coating are used for special purposes. Thesefilament lamps produce up to 35% more light on the illuminated area at the same current consumption.Halogen filament lamps are characterised by a longer life, a greater luminous efficiency and a higher colour temperature.Discharge lampsIn discharge lamps a solid, liquid or gaseous substance is caused to illuminate by an electrical discharge.Discharge lamps can be divided into low-pressure and high-pressure discharge lamps.Figure 1.4.1 shows an overview of the lamp systems.light generationtemperature radiatorsfilament lampsincandescentarc lampsdischarge lampshalogenfilament lampsmercury highpressure lampshigh-pressuredischarge lampssodium vapour highpressure lampshalogen metalvapour lampslow-pressuredischarge lampssodium vapour lowpressure lampsfluorescent lampscompactfluorescent lampshigh tension tubesinduction lampsFigure 1.4.1 Overview of the temperature and discharge lampsFundamental Principles of Lighting EngineeringLight Sources161.4.2Filament lampsIn filament lamps as shown in figure1.4.2.1 the light is generated by heating ofa helical tungsten wire (figure 1.4.2.2) totemperatures of approx.
2500 to 2700 °C.They therefore act as temperature radiators with a relatively poor luminous efficiency of only 10 to 15 lm/W.threadglass bulbfilamentFigure 1.4.2.2 Greatly magnified photo of a filament helixtop:double helix for filament lamps > 40 Wbottom: single helix for filament lamps from 25 W to 40 WFigure 1.4.2.1relative radiation in %100The power is only converted into lightto 5 to 15% as shown in figure 1.4.2.3,the rest is heat. The red part dominates in the visible range so that thelamp generates a warm-white light.8060402000380100078020003000λ / nmFigure 1.4.2.3 Relative spectral radiation distribution of a 40-Wfilament lamp.
Only part of the radiation is in the visible rangeAfter a certain time the light solid of afilament lamp vaporises and the lightcurrent is reduced by blackening ofthe light bulb and the life is shortened.The operating voltage of filamentlamps is decisive for their service life.Filament lamps should therefore neverbe operated with overvoltage but onlywith their rated voltage or much betterwith slight undervoltage.
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