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