Lumen (unit)
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The lumen (symbol: lm) is the SI unit of luminous flux.
Definition
1 lm = 1 cd·sr = 1 cd·m2·m–2
SI multiples
| Multiple | Name | Symbol | Multiple | Name | Symbol | |
|---|---|---|---|---|---|---|
| 100 | lumen | lm | ||||
| 101 | decalumen | dalm | 10–1 | decilumen | dlm | |
| 102 | hectolumen | hlm | 10–2 | centilumen | clm | |
| 103 | kilolumen | klm | 10–3 | millilumen | mlm | |
| 106 | megalumen | Mlm | 10–6 | microlumen | µlm | |
| 109 | gigalumen | Glm | 10–9 | nanolumen | nlm | |
| 1012 | teralumen | Tlm | 10–12 | picolumen | plm | |
| 1015 | petalumen | Plm | 10–15 | femtolumen | flm | |
| 1018 | exalumen | Elm | 10–18 | attolumen | alm | |
| 1021 | zettalumen | Zlm | 10–21 | zeptolumen | zlm | |
| 1024 | yottalumen | Ylm | 10–24 | yoctolumen | ylm | |
Explanation
If a light source emits one candela of luminous intensity into a solid angle of one steradian, the total luminous flux emitted into that solid angle is one lumen. Alternatively, an isotropic one-candela light source emits a total luminous flux of exactly [4\pi] lumens. The lumen can be thought of casually as a measure of the total "amount" of visible light emitted.A standard 100 watt incandescent light bulb emits approximately 1700 lumens. See the article on incandescent light bulbs for the specific efficiency of various types of electric light sources.
SI photometry units
| Quantity | Symbol | SI unit | Abbr. | Notes |
|---|---|---|---|---|
| Luminous energy | Qv | lumen second | lm·s | Talbots |
| Luminous flux | F | lumen (= cd·sr) | lm | also called luminous power |
| Luminous intensity | Iv | candela (= lumen (unit)>lm/sr) | cd | an SI base unit |
| Luminance | Lv | candela per square metre | cd/m2 | nits |
| Illuminance | Ev | lux (= lumen (unit)>lm/m2) | lx | |
| Luminous emittance | Mv | lux (= lumen (unit)>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 | |
See also
- Video projector for a discussion on lumen ratings of projectors.
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