What is Light? Sources and CIE recommended light sources ?

What is Light?


 J.C. Maxwell (1831) mentioned light as a type of electromagnetic radiation which propagate in the form of wave. In colour physics, light is that aspect of radiant energy of which human observer is aware through visual sensation arising from stimulation of retina by that radiant energy. Light has very high but finite speed (c) = 2.997925 X 108 m/sec or 1,86,000 miles/second in vacuum.

Sources of light:

1. Natural source of light (e.g. sun radiation)
2. Artificial source of light
    i) Thermal or incandescent source
    ii) Light emission due to excitation by electrical discharge

i) Thermal or incandescent source:
    Here, radiation is the result of high temperature of the objects.

ii) Light emission due to excitation by electrical discharge
   The distinction between the two classes is not very sharp. However, incandescent sources produce continous spectrum i.e. radiation all over a range of wave lengths where as electrical discharge results line spectra i.e. radiation at single wave length followed by a region in which no radiant energy is emitted.


Most of the practical sources of illuminations are the radiation from hot incandescent solid.
  1. Sun with a surface temperature of about 5000-6000C is an example of an incandescent source.
  2. In domestic lamp, tungsten filaments are heated to about 2100C.
  3. The carbon are having a temperature of about 4000C at the positive pole is the brightest man-made thermal source.

Light Option: 

A shade cannot always be assessed under one light rather several light option may be required. Because
  •  Application condition
  •  Artificial day light
  •  Point of sale
When two coloured material have identical spectral curve, they will be matched visually under any illuminant. However, it is possible for two material to match visually under one illuminant but miss-match under another, such matches are called as “Metameric match”. A pair of sample is said to be metameric if their colour match under one light source and do not match under different light source.


    CIE recommended light sources:


    What is Light? J.C. Maxwell (1831) mentioned light as a type of electromagnetic radiation which propagate in the form of wave. In colour physics, light is that aspect of radiant energy of which human observer is aware through visual sensation arising from stimulation of retina by that radiant energy. Light has very high but finite speed (c) = 2.997925 X 108 m/sec or 1,86,000 miles/second in vacuum. Sources of light: 1. Natural source of light (e.g. sun radiation) 2. Artificial source of light i) Thermal or incandescent source ii) Light emission due to excitation by electrical discharge i) Thermal or incandescent source: Here, radiation is the result of high temperature of the objects. ii) Light emission due to excitation by electrical discharge The distinction between the two classes is not very sharp. However, incandescent sources produce continous spectrum i.e. radiation all over a range of wave lengths where as electrical discharge results line spectra i.e. radiation at single wave length followed by a region in which no radiant energy is emitted. Most of the practical sources of illuminations are the radiation from hot incandescent solid. Sun with a surface temperature of about 5000-6000C is an example of an incandescent source. In domestic lamp, tungsten filaments are heated to about 2100C. The carbon are having a temperature of about 4000C at the positive pole is the brightest man-made thermal source. Light Option: A shade cannot always be assessed under one light rather several light option may be required. Because Application condition Artificial day light Point of sale When two coloured material have identical spectral curve, they will be matched visually under any illuminant. However, it is possible for two material to match visually under one illuminant but miss-match under another, such matches are called as “Metameric match”. A pair of sample is said to be metameric if their colour match under one light source and do not match under different light source. CIE recommended light sources: What is Light? J.C. Maxwell (1831) mentioned light as a type of electromagnetic radiation which propagate in the form of wave. In colour physics, light is that aspect of radiant energy of which human observer is aware through visual sensation arising from stimulation of retina by that radiant energy. Light has very high but finite speed (c) = 2.997925 X 108 m/sec or 1,86,000 miles/second in vacuum. Sources of light: 1. Natural source of light (e.g. sun radiation) 2. Artificial source of light i) Thermal or incandescent source ii) Light emission due to excitation by electrical discharge i) Thermal or incandescent source: Here, radiation is the result of high temperature of the objects. ii) Light emission due to excitation by electrical discharge The distinction between the two classes is not very sharp. However, incandescent sources produce continous spectrum i.e. radiation all over a range of wave lengths where as electrical discharge results line spectra i.e. radiation at single wave length followed by a region in which no radiant energy is emitted. Most of the practical sources of illuminations are the radiation from hot incandescent solid. Sun with a surface temperature of about 5000-6000C is an example of an incandescent source. In domestic lamp, tungsten filaments are heated to about 2100C. The carbon are having a temperature of about 4000C at the positive pole is the brightest man-made thermal source. CIE recommended light sources:




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