8.1 Night vision. Osram HQI-E 150 W/NDL CL
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If back reflecting construction elements are used in the luminaire design, the guarantee for the lamps can be restricted or even completely suspended.
It is therefore recommended contacting OSRAM if there is any doubt during the design stage.
It is useful to do comparative burning tests with non back reflecting luminaires. If in this case of e.g. ceramic lamps, visible deposits in the outer bulb of the lamps occur at an early stage in the tested luminaires, the burner has overheated due to back reflection.
In the case of lamps with back reflecting construction elements, tests should always be carried out to ascertain whether the extent of the lamp damage can at least be assessed as minimal.
Due to the fact that the failure rate of ceramic lamps depends on the switching frequency, a lamp test of this kind can be accelerated by increasing the switching frequency to e.g. 3h ON, 1h OFF.
8 Light and colour
Light is the part of the electromagnetic spectrum which can be seen with the eye. By definition, the perceptible wavelength range is 380-780 nm, although radiation can also be perceived as colour in the near infrared range. Similar to visible light, ultraviolet and infrared variation belong to the electromagnetic spectrum.
V’( λ)
(Night vision)
L < 0,1 cd/m 2
V(
λ)
(Day vision)
L > 30 cd/m 2
Fig. 43: Spectral brightness sensitivity
Light intensity
Light intensity
Light intensity is the measure of lightoutput in a specified direction.
Fig. 41: Visible light as part of the electromagnetic spectrum
Unit: 1 candela (cd)
Fig. 44: Definition of luminous intensity
Different wavelengths can be perceived to different extents. The maximum of the sensitivity curve for photopic vision is at 555 nm. The light output (luminous flux) is ascertained by multiplying the physical radiation output with the eye sensitivity curve V(λ)
(see Fig. 43).
Illumination
Average illumination of a surface is luminous flux per unit area.
If the entire radiation output is emitted monochromatically in the wavelength of maximum eye sensitivity
(555 nm), then the theoretical maximum luminous efficacy is 683 lm/W. With uniform distribution of radiation over the range of 380 – 780 nm, approx. 196 lm/W is possible.
Lux
Fig. 45: Definition of illuminance
Luminous flux
Luminous flux is the light output of a light source.
Unit: 1 lumen (lm)
Fig. 42: Definition of luminous flux
Luminance
visible surface
Light intensity illuminated surface
Luminance is the measure of the brightness that the eye has of a surface.
Unit: 1 candela/m 2 (cd/m 2 )
Luminance depends on the surface of the area seen by the eye and on the luminous intensity, radiated from the surface towards the eye.
Fig. 46: Definition of luminance
Luminous = Irradiated light in Lumen (lm) (Gl. 9.1) efficacy spent electrical power in watt
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