Integrating Sphere Simulation on Spatial Nonuniformity Errors in Luminous Flux Measurement
Yoshihiro Ohno, R O. Daubach
An integrating sphere simulation program, previously developed for the realization of the luminous flux unit at NIST, has been utilized to analyze spatial nonuniformity errors in integrating sphere photometers for substitution measurement of total luminous flux of lamps. The program simulates interreflections in an integrating sphere and calculates the final luminance distributions on the sphere wall as well as the detector output. Using this program, a series of simulations has been conducted on a 2 m integrating sphere having a 30 cm circular baffle, with varied sphere wall reflectance (p = 80 % to 98 %) and baffle reflectances, the size and location of the baffle, and the angular response of the detector. Measurement errors (with respect to an isotropic point source) were calculated for actual intensity distribution data of eight different types of incandescent and discharge lamps. The results show that, with a well-designed integrating sphere photometer with no contamination of coating, measurement uncertainties (k = 2) on the order of 1 % (p = 80 %) to 0.1 % (p = 98 %) can be expected for typical general service lamps with no reflectors, measured against a calibration source of uniform intensity distribution. Larger errors are shown with integrating sphere systems not properly designed.