Measurement of Stray Light in a Monochromator*

In spectrophotometry and spectroradiometry photometric errors due to stray light passed by the monochromator employed are always present to some degree. The magnitude of the errors is dependent upon the spectral distribution of the energy entering the monochromator, the stray light characteristics of the monochromator, the effects of any filters or other components between the monochromator and the phototube, and the spectral response of the phototube or other receptor. Means are outlined of measuring the stray light characteristics of a monochromator and expressing the results in the form of a table or grid of numbers. From the grid values it is a relatively simple process to estimate closely the photometric errors in any given application. Finally, various means are suggested of reducing the effects of stray light errors.