Abstract

A spectroradiometer is described for recording the spectral distribution of daylight or of any artificial light source that radiates steadily for 3.5 min. Beams from the external source and from an internal standard lamp are deviated alternately through a monochromator to a multiplier phototube. The collimator consists of parallel baffles instead of a mirror or lenses. The amplified signal activates a motor which moves a mirror to attenuate the energy from the internal standard until the beams are equal. The necessary degree of attenuation is then recorded while the wavelength is being changed. The logarithm of the spectral distribution of the internal standard may be added electrically to the logarithm of the measured attenuation to record directly the logarithm of the absolute energy radiated by the sample. The spectral distribution of sources with luminances as low as 1 ft-L have been measured with a half-maximum band width of 10 mμ. The spectral emittance of a variety of phases of daylight and sunlight, at different times of the year and under various weather conditions, as well as of fluorescent lamps, electroluminescent panels, and ultraviolet-excited fluorescent coatings, have been recorded and are summarized here.

© 1958 Optical Society of America

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