Light and Colour Theories, and their relation to light and colour standardization

by Joseph W. Lovibond

A RESIDUAL RED RAY.

Apart from the colours of everyday life there is, in sunlight and most direct artificial lights, an additional red energy which differs materially from the red energy in diffused daylight.

It was first noticed whilst establishing the colour equivalence of the tintometrical light unit, by developing a red sensation which disturbed constancy of reading under certain conditions of light.

So far as the writer knows, this energy has never been investigated as separate from the other spectrum red. The following observations must be considered as tentative only.