LUMINOUS-FLUX MEASUREMENTS BY AN ABSOLUTE INTEGRATING SPHERE

We present an original implementation of the absolute-sphere method re cently proposed by Ohno. The luminous-flux unit, the lumen, is realize d by means of an integrating sphere with an opening calibrated by a lu minous-intensity standard placed outside. The adapted experimental set up permits one to measure luminous-flux values between 5 and 2500 lm w ith a significant improvement with respect to the simulated performanc es reported in the literature. Traditionally, the luminous-flux unit, the lumen, is realized by goniophotometric techniques in which the lum inous-intensity distribution is measured and integrated over the whole solid angle. Thus sphere results are compared with those obtained wit h the Istituto Elettrotecnico Nazionale goniophotometer. In particular , a set of standards, characterized by luminous-flux values of similar to 2000 lm, has been calibrated with both techniques. We highlight so me of the problems encountered. Experimental results show that the agr eement between the two methods is within the estimated uncertainty and suggest promising areas for future research. (C) 1996 Optical Society of America