A Simple Method of Heterochromatic Photometry

Abstract

AS is well known, it is difficult to compare the intensities of lights of different colour. We can tell when one is much brighter or much darker than the other, but values obtained for the point of balance by the direct methods differ widely amongst themselves. It is consequently necessary to use the flicker photometer or the step-by-step method; in the latter method a series of lights of different colours intermediate between the colours to be compared is used, and the one end colour is compared with the first of these, the first with the second, the second with the third and so on. Thus by reducing the difference in colour its disturbing effect is eliminated at the expense of some time and a cumulative error in the settings.