# Lumen second

(Redirected from Lumberg (unit))

In photometry, the lumen second (lm s or lm⋅s) is the SI derived unit of luminous energy. 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.[1] 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.

An older name for the lumen second was the lumberg.[citation needed]

The photometric unit lumerg, also 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 107 lumerg = 1 lm⋅s.[1]

SI photometry units
Quantity Unit Dimension Notes
Name Symbol[nb 1] Name Symbol Symbol
Luminous energy Qv [nb 2] lumen second lm⋅s TJ [nb 3] units are sometimes called talbots
Luminous flux Φv [nb 2] lumen (= cd⋅sr) lm J [nb 3] also called luminous power
Luminous intensity Iv candela (= lm/sr) cd J [nb 3] an SI base unit, luminous flux per unit solid angle
Luminance Lv candela per square metre cd/m2 L−2J units are sometimes called nits
Illuminance Ev lux (= lm/m2) lx L−2J used for light incident on a surface
Luminous emittance Mv lux (= lm/m2) lx L−2J used for light emitted from a surface
Luminous exposure Hv lux second lx⋅s L−2TJ
Luminous energy density ωv lumen second per metre3 lm⋅sm−3 L−3TJ
Luminous efficacy η [nb 2] lumen per watt lm/W M−1L−2T3J ratio of luminous flux to radiant flux
Luminous efficiency V 1 also called luminous coefficient