Kruithof curve

Named after the Dutch engineer Arie Andries Kruithof, [cite web|first=Arie Andries|last=Kruithof|url=http://dap.library.uu.nl/cgi-bin/dap/dap?diss_id=7789|title=Aanslag van het waterstofmolecuulspectrum door electronen|month=December 12|year=1934 (PhD dissertation at Utrecht University under Leonard Ornstein) nl icon] the Kruithof curve relates the illuminance and colour temperature of visually-pleasing light sources.

The colour sensation of a given light mixture may vary with absolute luminosity, because both rods and cones are active at once in the eye, with each having different colour curves, and rods taking over gradually from cones as the brightness of the scene is reduced. This means, for example, that light with a colour temperature of 6000 K may appear white under high luminance, but appear bluish under low luminance. Under the same low luminance conditions, the colour temperature may need to be adjusted to, say, 4700 K, to appear white. This effect leads to a change in colour rendition with absolute illumination levels that can be summarised in the empirical Kruithof curve.cite journal |last=Kruithof|first=Arie Andries|title=Tubular Luminescence Lamps for General Illumination |journal=Philips Technical Review| volume=6|issue=3|pages=65–96|year=1941|issn=0031-7926]

As the brightness of the scene decreases, the brightness of red colours decreases more rapidly than those of blue colours, this being the so-called Purkinje effect.cite book | author=Frisby, John P. | title=Seeing: Illusion, Brain and Mind | publisher=Oxford University Press |location=Oxford | year=1980|isbn=978-0192176721] pn

References

Further reading

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* (A study in which the average luminance was 8 cd/m², or the illumination 200–400 lux, with an average of about 330 lux.)

External links

* [http://www.soluxtli.com/edu13.htm Daylight: Is it in the eye of the beholder?] by Kevin P. McGuire.