What is Illuminants?

Illuminants: 

Illuminants are standard light sources defined by specific spectral power distribution (SPD). A source is physical emitter of light e.g. sunlight, candle or a lamp. Illuminant refers to the theoretical data on relative energy at each of visible as well as at near uv range of light. Commission Internationale de l’Éclairage (CIE) i.e. The international Committee that formulate colour & illuminant standards established in 1931 recommended three illuminants

1. Illuminant A
2. Illuminant B
3. Illuminant C

1. Illuminant A

Standard illuminant A was designed in 1931 to be representative of indoor artificial (tungsten lamp) illumination and is defined as an illuminant having the same SPD as a Planckian radiator at a temperature of about 2856 K and CRI = 100. An actual source corresponding to this illuminant is readily achieved, and calibrated standard tungsten lamps are available from standardising bodies in each country. Such an illuminant is relatively yellowish in colour as it is deficient in power in the blue end of the visible spectrum and rich in the red wavelengths (Figure 1.9).

2. Illuminant B

Standard illuminant B, with a correlated colour temperature (CCT) of about 4870␣ K, was supposed to represent daylight plus sunlight,

3. Illuminant C

Standard illuminant C (CCT = 6770 K) was intended to represent average daylight.

    4. D65 :

In 1964, CIE introduce another standard illuminant D65 . It is better representation of illumination of average day light as it is average of day light from early morning to late evening, from blue sky to completely overcast condition and at different latitude.

•  Colour temperature = 6500 K
•  CRI = 98

5. D75 :

In 1971, CIE introduced another artificial illuminant representing artificial day light which is popular in some part of American for colour assessment where a bluer phase of day light is preferred.

•  Colour temperature = 7500 K
•  CRI = 96
•  ASTM Standard.

6. D50 :

In 1984, CIE introduced D50 which is recommended for graphic art trade for illumination of colour prints and photograph.

•  Colour temperature = 5000 K
•  CRI = 98