CLOSE cooperation of Committees of the International Commission on Illumination, the International Organization for Standardization, the International Electrotechnical Commission, and the SUN Commission of the International Union of Pure and Applied Physics is resulting in the development of a set of terms and symbols that should, and hopefully will, receive acceptance throughout the entire world. The symbols in the USA Standard Letter Symbols for Illuminating Engineering are consistent with the international agreements that have been reached to date.
The outstanding features of the symbols in this Standard are (1) the use of the same set of symbols for radiometric and photometric quantities with the proviso that when there is need to differentiate these quantities subscripts e and v, respectively, will be used, and (2) the use of a subscript λ to designate a spectral concentration and λ in parenthesis to designate a function of wavelength (the adjective spectral is used in English to indicate both of these meanings, but in French, the adjective spectrique is substituted for spectral for the first meaning when there is a need to avoid ambiguity).
This standard was prepared by Subcommittee of Sectional Committee Y10. Following its approval by the Sectional Committee and the sponsor, it was approved by the USA Standards Institute on February 2, 1967.