Talbot (photometry)
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In photometry the talbot (T) is a nonstandard unit of luminous energy, named in honor of the early photographer William Fox Talbot. It is exactly equal to the SI standard unit, the lumen · second:
- 1 T = 1 lm · s
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| Quantity | Symbol | SI unit | Abbr. | Notes |
|---|---|---|---|---|
| Luminous energy | Qv | lumen second | lm·s | units are sometimes called talbots |
| Luminous flux | F | lumen (= cd·sr) | lm | also called luminous power |
| Luminous intensity | Iv | candela (= lm/sr) | cd | an SI base unit |
| Luminance | Lv | candela per square metre | cd/m2 | units are sometimes called nits |
| Illuminance | Ev | lux (= lm/m2) | lx | Used for light incident on a surface |
| Luminous emittance | Mv | lux (= lm/m2) | lx | Used for light emitted from a surface |
| Luminous efficacy | lumen per watt | lm/W | ratio of luminous flux to radiant flux; maximum possible is 683.002 |
