Index of returned color

The index of returned color or IRC is the capacity of a source of Lumière to restore different the Couleur S from the visible spectrum without modifying the colors of them. The general index of returned colors Ra determines the quality of a light starting from the index of returned of 8 standardized colors. The maximum index Ra=100, corresponds to a white light having the same spectrum as that of solar light (see Rayonnement black Corps).

light of day is by definition of Ra=100.
the incandescent lamps are close to Ra=100.
the gas-discharge lamps have a variable IRC which depends on gas contained in the bulb and the fluorescent powder placed inside the tube.
the fluorescent tubes have an IRC from 60 to 90. Fluorescent the tubes known as “white industry” or “universal white” have a poor IRC and give sometimes these dyes “blafards” or “greenish” which gave a bad reputation to the fluorescent tubes.
Certaines lamps used in the road or highway sector is lamps with sodium high pressure. It is their particularly low IRC (25), and not them Température of color (red orange), which explains the modification of the colors of body of the cars. One could say while simplifying coarsely that an IRC of 25 restores only one quarter of the nuances of the spectrum. The lamps with the sodium-low pressure have an IRC equal to 20, very poor with a quasi-monochromatic light in yellow.
the lamps with metal halides have an IRC ranging between 60 and 95, therefore very good returned colors, compared with sodium high-pressure. The lamps with mercury with a fluorescent coating, have an IRC ranging between 35 and 60, but a spectrum not very rich colors.

The IRC is, with the Température of color, the second factor making it possible to qualify a source of light.

External bonds

IRC and temperature of the colors (energy and environment)
Example of bulb fluocompacte with high IRC

Category: photometry Category: colorimetry

Index of Returned Colors

The Index of returned colors, or IRC, is a measurement of the quality of the light, standardized by the International commission of lighting (Co). It consite in a scale varying of 0, for the light emitted by a monochromatic lamp such as a bulb with mercury vapors, until 100, for a source of light with incandescence. The IRC (English CRY) is a percentage of recognition of the colors, in a given light, compared to an ideal, such as the light emitted by the radiation of the black body.

The IRC is related to the Température of color, in that, the IRC of two sources of light has direction only insofar as the temperature of color emitted by the two estla sources even. for example a fluorescent tube standard " cool white" an IRC of 62 has The IRC is not a subjective data but is quantitatively measurable. It is defined compared to a source of reference, radiant like a black body, to which one affects value 100. (Therefore the incandescent lamps, which radiates like black bodies, have an IRC of 100) and the source to be tested, having same the Température of color is compared to him. One uses these two sources to light several standard samples. The colors perceived with the reference and the source to be tested (measured according to standard Co 1931) are compared using a traditional formula, and one makes an average on all the samples (in general eight) to obtain the IRC. As eight one often use eight samples, the manufacturers often use the prefix " octo-" for their lamp with high IRC.

Standard The formulated consists off taking the color differences ΔEi, between the test color and the eight samples, one the 1964 W*U*V* uniform color space (which is now obsolete). The color rendering index IH is calculated for each off the eight samples:

R_i=100-4.6 \ Delta E_i \,

which gives the color rendering index with respect to each sample. General The color rendering index Ra is then the average off thesis eight separate indices.

External link

* To calculate CRY (http://www.kruschwitz.com/cri.htm) formulated

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