{{short description|SI unit of luminous energy}} {{infobox Unit | name = lumen-second | standard = SI | quantity = luminous energy | symbol = lm·s }} In photometry, the '''lumen second''' ('''lm⋅s''') is the unit of luminous energy in the International System of Units (SI). It is based on the lumen, the SI unit of luminous flux, and the second, the SI base unit of time.
The lumen second is sometimes called the '''talbot''' (symbol '''T'''). This name was coined in 1937 by the Committee on Colorimetry, Optical Society of America, in honor of the early photographer William Fox Talbot.<ref name="Loyd_1937_Nomenclature" /> The talbot is exactly equal to the lumen second: : 1 T = 1 lm⋅s
The use of the symbol T for talbots conflicts with T as the symbol for the tesla, the SI unit of magnetic flux density.
The photometric unit '''lumerg'''<ref name="Loyd_1937_Nomenclature"/> or '''lumberg''',<ref>{{cite book |title=Dictionary of Scientific Units: Including dimensionless numbers and scales |first1=H. G. |last1=Jerrard |first2=D. B. |last2=McNeill |edition=6th |publisher=Springer Science & Business Media |year=2012 |isbn=9789401122948 |page=92 |url=https://books.google.com/books?id=tjz6CAAAQBAJ&dq=loudness+lumberg&pg=PA92 }}</ref> proposed by the Committee on Colorimetry in 1937, correlates with the old CGS unit erg in the same way that the lumen second correlates with the radiometric unit joule, so that {{nowrap|1=10<sup>7</sup> lumerg = 1 lm⋅s}}.<ref name="Loyd_1937_Nomenclature">Loyd Ancile Jones. ''Colorimetry: Preliminary draft of a report on nomenclature and definitions''. Journal of the Optical Society of America, Volume 27, page 211 (June 1937): "Referring again to Table I, terms (21) and (22) represent names for units which the committee has voted to adopt. The decision was almost unanimous<!-- votes: 16:2 --> in the case of recommending talbot as a psychophysical correlate of joule. The vote on lumerg as the psychophysical correlate of the erg was less unanimous<!-- votes: 11:9 -->."</ref>
{{SI_light units}}
== References == <references />
Category:Units of luminous energy Category:SI derived units Category:Second