Proposed changes to the SI system of photometric units

Abstract

It has recently been proposed that the lumen should become the SI base unit for photometry and that it should be defined in terms of the SI unit of power, the watt. The freezing platinum primary standard source would then be replaced by a primary standard detector, for example an absolute radiometer. As a preliminary measure 683 lm/W has been adopted as the conventional value for Km for use in spectroradiometric calculations. The reasoning behind these changes is briefly presented, together with some discussion of the implications.