ABSTRACT
SUMMARY A rig was built comprising a quadrant beam, pivoted at the top about a vertical axis and movable at its foot which was located on a semi-circular track, as shown the figure. The lamp holder and reflector were mounted on this quadrant and could be moved to each of the 28 positions defined by elevation r and azimuth B. The specimen was precisely located in a tray on three footscrews allowing precise height and level adjustments. The illuminance on the sample was measured by replacing it with a 98% diffuse reflectance plate and using a spectroradiometric luminance spot-meter. The luminance of the sample was measured with an electronic luminance camera mounted to encompass the viewing angle of le below the horizontal and also with the luminance meter at 3.5e below the horizontal. This greater angle was for practical reasons.
