A study on the spectral energy distribution of a tungsten filament lamp based upon the results obtained by the summation of black body radiations at different temperatues

Abstract

It is already known that when the temperature of tungsten lamp is set to give the same red-blue ratio as the black body at a particular temperature the green part of the spectrum of the radiation from the tungsten filament is relatively higher than that of the black body. The difference seems ascribable to the selective emissivity of the tungsten filament and the non-uniformity in the temperature distribution along the filament.In order to investigate the latter's effect, the distribution of the color temperatures along the filament has been measured. Assuming that each part of the filament is a black body, authors calculated the spectral energy distribution of the total light from the filament and found that the resultant radiation had almost the same spectral distribution as that of the black body at a certain temperature. According to the results obtained, it is considered that the difference of the spectral energy distribution between the tungsten filament lamp and the black body depends mainly upon the selective emissivity of the tungsten filament and slightly on the non-uniformity of the filament temperature.Moreover, in the case of the summation of black body radiations at differet temperatures, the temperature of the black body wkich gives the nearest spectral distribution to that of the resultant radiation is easily calculated with suitable weight which is estimated at T 9-T 11.