A Perkin-Elmer Lambda 1050 spectrophotometer is used to complement the reference reflectance and transmittance instruments. It performs this function by measuring samples relative to standards calibrated on the reference instruments. The instrument measures non-fluorescent samples at room temperature. The conditions of measurement and measured quantities for this instrument are given below. The illuminator has two sources, a deuterium (D2) arc lamp and a quartz-tungsten-halogen incandescent lamp, order-sorting filters, a double-grating monochromator, and a chopper. The sample compartment has two beams, one for the reference and one for the sample. Integrating sphere accessories are added for diffuse reflectance and transmittance measurements. The receiver has collection optics and photomultiplier tube (PMT), indium-gallium-arsenide (InGaAs), and lead sulfide (PbS) detectors.