Abstract
It is proposed (1) that the basic photometric unit be redefined so as to provide an exact numerical relationship between it and the SI unit of power, the watt, for a specified monochromatic radiation; and (2) that the unit of luminous intensity, the candela, be replaced as the basic unit by the unit of luminous flux, the lumen. It is claimed that the existing definitions are predominantly the product of early photometric practices that have been superseded. A closer link between photometry and spectroradiometry is now desirable. The proposals would enable photometric values to be derived from spectroradiometric data by exact computation, and would remove the need for a primary standard of light. They would not alter significantly the present magnitudes of the photometric units, nor change the existing relationship between photometry and visual perception. Because the proposed redefinitions are in terms of monochromatic rather than complex radiation, however, they would provide a more convenient basis for the future adoption of new spectral weighting procedures.