Page:Journal of the Optical Society of America, volume 33, number 7.pdf/29

 TRICHROMATIC

SPECIFICATIONS

TABLE II. Trichromatic specification, dominant wavelength, and excitation purity for neutral grays; half-steps of Munsell value, and a special series of small value steps.


 * r1 More than one lot of this color has been made (March, 1943).

puted colorimetric values for the curves. About 1000 colors were involved.

Spectral apparent reflectance curves were made on the General Electric Recording Spectrophotometer. The standard of reflectance was thick, of magnesium oxide. All samples were

backed by a non-selective diffusing surface having an apparent reflectance of 0.005.

The wave-length calibration of the spectrophotometer is shown by the curve in Fig. 1. This curve was obtained by drawing a smooth line through the mean of points representing the wave-length error as determined by observation of a mercury discharge tube, and measurements on two filters calibrated by the National Bureau of Standards and the Color Measurements Laboratory at the Massachusetts Institute of Technology. It is believed that this calibration was maintained within +0.5 mμ in the wave-length region used for the colorimetric computations.

The General Electric Recording Spectrophotometer as originally manufactured allows the sample and standard to be irradiated normally and viewed diffusely, except that approximately one-half of the specular component is lost by being reflected through the entrance apertures. During the course of this work, the viewing geometry was changed to permit total inclusion or exclusion of the specular component. This change allowed the sample and standard to be irradiated at 5° from the normal, and viewed diffusely, with provision to include or exclude the specular component.

Therefore, some of the reflectance curves were made with the original viewing geometry, while the remainder were run with the new viewing the surface of a freshly prepared layer, 0.06 inch geometry, specular component included. Experi