Filters to Colour-Match Tungsten Filament Lamps with Sodium-Vapour Lamps

Abstract

A description is given of the properties of four filters which may be used to measure the luminous intensities of sodium-vapour lamps if tungsten filament lamps are used as intensity standards. In particular, a filter made at the laboratory from Chance OB 2 and OY 1 glasses is described. It enables the measurements to be made under colour-match and approximately energy match conditions. This filter is compared with the Zeiss glass filter used at the laboratory. The spread in the results of six observers is about per cent. with the Chance glass filter described and about 7 per cent. with the Zeiss glass filter. The mean values of the readings obtained with each of the filters agree to about 2 per cent. The colour, transmission, and temperature coefficients of colour and transmission of the Chance glass filter are given. Other filters which may be suitable for this purpose are Corning 978 with Chance OY 1 glasses or the combination of Wratten 23B and Wratten 57 gelatine filters.