Lighting engineering elements
COLOUR TEMPERATURE
PHOTOMETRIC CURVES
Colour temperature is used in lighting engineering to identify the hue of light. Its unit of measurement is the kelvin (K). The spectrum of light emitted by a black body has a peak emission determined by its temperature. This same principle can be applied to a light source even though it differs from the black body. The colour temperature of a given light radiation is therefore considered as the temperature that a black body should have so that the light radiation emitted by it is chromatically as similar as possible to the radiation considered. For example a temperature of about 2,000 K will give a yellow-orange colour. Lowering this threshold, we will have red and afterwards infrared, i.e. wavelengths that are no longer visible to the human eye. Increasing the temperature, on the other hand, will gradually give a whiter light until reaching blue-violet and finally ultraviolet. In brief, a warm light will have a low colour temperature and a cool light will have a high colour temperature.
Photometric curves consist of a two-dimensional representation (vertical planes passing through the optical centre of the luminaire) of the photometric solid i.e. the intensity emitted in all directions from the light source. The luminous intensity distribution is normally represented in the two main planes that are perpendicular to each other. angoli gamma
180
150
120
105
105
90
90
75
100
75
60
200
60
300
45
45 400
cd/klm
500
30 0° - 180°
UNITS OF MEASUREMENT Quantity
Radiometric
Photometric
power
watt (W)
lumen (lm)
power per unit area
W/m2
lm/m2 = lux (lx)
power per unit solid angle
W/sr
lm/sr = candela (cd)
power per area per solid angle
W/m2 - sr
lm/m2 - sr = cd/m2 = nit
LOR LOR (light output ratio) is the ratio between the flux emitted by the luminaire and the total flux of the lamp contained in it (Φu/Φtot). Being a ratio of two quantities of the same type, LOR is generally expressed as a percentage.
1800 K WARM LIGHT Low colour temperature
XXII
4000 K
5500 K
15
0
15
30
90° - 270°
ISOLUX CURVES Isolux curves represent the union of the points of the plane having the same value of illuminance (lux).
max = 28 lx/klm 3.0h 2 2 2.5h 4 2.0h 7 10 1.5h 16 13 1.0h 4 19 22 0.5h 25 1 1 0.0h 2 2 -0.5h 4 -1.0h 7 10 -1.5h -2.0h 4 -2.5h -3.0h -3.0h -2.0h -1.0h 0.0h 1.0h 2.0h 3.0h
8000 K
12000 K
16000 K COOL LIGHT High colour temperature