| Lumen second | |
|---|---|
| Unit system | SI |
| Unit of | luminous energy |
| Symbol | lm·s |
Inphotometry, thelumen second (lm⋅s) is the unit ofluminous energy in theInternational System of Units (SI). It is based on thelumen, the SI unit ofluminous flux, and thesecond, theSI base unit of time.
The lumen second is sometimes called thetalbot (symbolT). This name was coined in 1937 by the Committee on Colorimetry,Optical Society of America, in honor of the earlyphotographerWilliam Fox Talbot.[1] The talbot is exactly equal to the lumen second:
The use of the symbol T for talbots conflicts with T as the symbol for thetesla, the SI unit of magnetic flux density.
The photometric unitlumerg[1] orlumberg,[2] proposed by the Committee on Colorimetry in 1937, correlates with the oldCGS uniterg in the same way that the lumen second correlates with theradiometric unitjoule, so that107 lumerg = 1 lm⋅s.[1]
| Quantity | Unit | Dimension [nb 1] | Notes | ||
|---|---|---|---|---|---|
| Name | Symbol[nb 2] | Name | Symbol | ||
| Luminous energy | Qv[nb 3] | lumen second | lm⋅s | T⋅J | The lumen second is sometimes called thetalbot. |
| Luminous flux, luminous power | Φv[nb 3] | lumen (= candelasteradian) | lm (= cd⋅sr) | J | Luminous energy per unit time |
| Luminous intensity | Iv | candela (= lumen per steradian) | cd (= lm/sr) | J | Luminous flux per unitsolid angle |
| Luminance | Lv | candela per square metre | cd/m2 (= lm/(sr⋅m2)) | L−2⋅J | Luminous flux per unit solid angle per unitprojected source area. The candela per square metre is sometimes called thenit. |
| Illuminance | Ev | lux (= lumen per square metre) | lx (= lm/m2) | L−2⋅J | Luminous fluxincident on a surface |
| Luminous exitance, luminous emittance | Mv | lumen per square metre | lm/m2 | L−2⋅J | Luminous fluxemitted from a surface |
| Luminous exposure | Hv | lux second | lx⋅s | L−2⋅T⋅J | Time-integrated illuminance |
| Luminous energy density | ωv | lumen second per cubic metre | lm⋅s/m3 | L−3⋅T⋅J | |
| Luminous efficacy (of radiation) | K | lumen perwatt | lm/W | M−1⋅L−2⋅T3⋅J | Ratio of luminous flux toradiant flux |
| Luminous efficacy (of a source) | η[nb 3] | lumen perwatt | lm/W | M−1⋅L−2⋅T3⋅J | Ratio of luminous flux to power consumption |
| Luminous efficiency, luminous coefficient | V | 1 | Luminous efficacy normalized by the maximum possible efficacy | ||
| See also: | |||||