Calibration of a Laboratory Spectrophotometer for Specular Light by Means of Stacked Glass Plates

Stacked glass plates have been used to calibrate a laboratory spectrophotometer, over the spectral range 0.5–2.5 μ, for specular light. The uncalibrated instrument was characterized by systematic errors when used to measure the reflectance and transmittance of stacked glass plates. Calibration included first, a determination of the reflectance of a standard composed of barium sulfate paint deposited on an aluminum plate; second, the approximation of the reflectance and transmittance residuals between observed and computed values by means of cubic equations; and, finally, the removal of the systematic errors by a computer. The instrument, after calibration, was accurate to 1% when used to measure the reflectance and transmittance of stacked glass plates.