Colors Produced by Reflection at Grazing Incidence from Rough Surfaces*

Using a precision spectrometer with a photomultiplier attached to its telescope, the specular reflection of light from various rough surfaces was measured at angles of incidence in the region 80° to 89°. Seven interference filters were used to isolate spectral bands covering the visible spectrum. From the measured values of reflectance the chromaticity of the specularly reflected light was computed, assuming CIE source “A” for the incident light. It was found that at all angles the resulting colors lay in a narrow region near the Planckian locus, being more reddish than the incident light. The maximum redness was found at an angle where the specular reflectance had already become small. It is shown to be likely that if the specularly reflected light could be isolated the surface would form an accurate means of reducing color temperature.