Keywords:

Abstract:

This article continues investigations reported in Conservation 5 (1960), p. 41. In Crawford's method observers are faced with objects illuminated by light closely approximating black body radiation of a given colour temperature. This light is then imperceptibly changed to light from the source under investigation, say a fluorescent tube. Since daylight is close to black body radiation, the light is in effect switched from daylight of the kind the fluorescent tube is intended to imitate to the fluorescent light itself. With appropriate checks, the observers reactions are reported. They are then analyzed on the basis of a division of the visible spectrum into six bands. Any illuminant can thus be given a class designation such that class A satisfies 95% of all observers. Crawford's investigations show that there is no fluorescent tube yet on the market which can be put into colour rendering class A. Tubes in colour rendering class B include the Atlas Northlight and the Philips Colour 34. Garry Thomson