an archaic unit of luminous exitance equal to 1 lumen per sq cm (1m/cm2). The name “radphot” was derived from phot, a unit of illuminance. It was proposed by the French physicist A. Blondel and included in 1928 in the recommendations of the International Commission on Illumination (CIE). In 1951 the CIE recommended that the unit for luminous exitance should be 1m/m2.
In the USSR radphot was used after 1932 (Sectorial Standard of the All-Union Committee on Standardization 4891). In 1948 the Statute on Photometric Units defined radphot as the unit of luminous exitance equal to 10,000 rlx (radlux). The radphot is abbreviated rph. The unit was not included in the All-Union State Standard 7932–56, Photometric Units.