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You are here:HomeLearn Lighting1.2-2----Characterising a light source
1.2-2----Characterising a light source

1.2.2 Color rendering
The color rendering index gives the capacity of a source to restore the colors of an illuminated object with regards to an ideal source. The  color rendering depends on th spectrum of light emitted. The more this spectrum is conditions and thereby close to that of sunlight, the better shall be its rendering. A light source may be used for general lighting as soon as its color rendering exceeds 80%.
For an incandescent light source
>>An incandescent light source has a color rendering index close to 100%

For a discharge luminescent source or LED
>>A TL tube or a compact fluorescent lamp may have color rendering indices from 80 to more than 90%
>>A white LED produced from a blue LED covered with yellow phosphor generally had bad color rendering (<80), as the emitted light lacked red and did not restore this color correctly. Today, we find white LEDs with a color rendering index greater than 80.
>>When the color rendering index exceeds 80 it is specified in the technical characteristics of the LED.
>>A low-pressure sodium lamp (used for lighting roads) has a rendering of 22, nearly monochromatic emission of yellow.

1.2.3The luminous flux (in lumen [lm])
This is the visible energy/time unit. A power of 1W radiated by a source at a wavelength of 555nm has a luminous fulx of 683 lumens (see point 1.3.2).