Influence of aperture size on the photometry of retroreflectors

The size of the source and receptor apertures used in the photometry of retroreflectors must be sufficiently small for geometric accuracy yet large enough to send and receive measurable quantities of light. This study uses a computer integration technique to calculate numerically the error in measurement due to various sizes of apertures. The calculations are based on highly resolved observation angle curves of four types of retroreflector obtained by direct measurement.