A method of obtaining a measure of the stickiness of heated particulate solids includes pouring a sample of the particulate solids onto a generally horizontal support and allowing it to freely form its own angle of repose. Etch stop layers are used to form contacts to the n-type ohmic contact layer and contacts to the n-type modulation doped quantum well structure. Two second elliptic group reflecting surfaces can be provided that are shaped as substantial halves of elliptical surfaces. Each of the plurality of luminance levels and the corrected luminance level in the extension correcting table memory corresponding thereto are mixed in the mixture ratio.