<title>New standard for the candela at the CSMU</title>

Abstract

A method of luminous intensity measurement in accordance with new definition of candela adopted by the 16th International Committee of Weights and Measures in 1979 is described. Principal emphasis is placed in applying selfcalibrated photodiodes to the spectroradiometric measurements. The results of luminous intensity measurements with the CSMU photometric standard lamps are given. INTRODUCTIONThe relation between radiometric and photometric quantity is given by equationwhere)i and A2 are the limits of wavelength range in the visible. Spectral radiant intensity is a radiant quantity related to radiant flux by the equationwhere the spectral radiant flux. The solid angle over which light is collected is defined by the aperture area and the lamp/photometer distance. Luminous intensity in the relation (2) can be determined applying two main methods -broad-band photometry and spectroradiometric photometry. PRINCIPLE OF THE SPECTRORADI.QMETRLc REALIZATIONThe realization of the candela therefore involves dispersion of the radiation by a monochromator into spectral components. They are measured separately and the value of luminous intensity is determined numerically. There are several considerations behind the decision to use silicon photodiode detectors in the realization, rather than based on thermal device one. In recent years O-8194-1456-5/93/$6.OO SPIE Vol. 2161 Photometry (1993) / 133 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 07/04/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx