Photometry measures guide
Lighting is science, and we’ve come a long way from wooden fire and candle light. But if we look into the different lighting technologies, there has been a serious advancement in the efficiency and luminous output of the lamps and luminaires. Behind this advancement there are different measures to determine the quality of the light. Here is a quick summary of the different terms and descriptions:
| Quantity | Unit | Dimension | Notes | ||
| Name | Symbol (1) | Name | Symbol | Symbol | |
| Luminous energy | QV (2) | Lumen per second | lm-s | T*J (3) | Units are sometimes called talbots |
| Luminous flux/ luminous power | ØV (2) | Lumen (=cd*sr) | Lm | J (3) | Luminous energy per unit time |
| Luminous intensity | lV | Candela (= lm/sr) | Cd | J (3) | Luminous flux per solid angle |
| Luminance | LV | Candela per square metre | Cd/m2 | L-2* J | Luminous flux per unit solid angle per unit projected source area. Units are sometimes called nits. |
| Illuminance | EV | Lux (= lm/m2) | Lx | L-2* J | Luminous flux incident on a surface. |
| Luminous exitance / Luminous emmittance | MV | Lux | Lx | L-2* J | Luminous flux emitted from a surface |
| Luminous exposure | HV | Lux per second | Lx*s | L-2* T * J | |
| Luminous energy density | ωV | Lumen second per cubic metre | lm*s*m-3 | L-3* T * J | |
| Luminous efficacy | η(2) | Lumen per watt | lm/W | M-1*L-2*T3*J | Ratio of luminous Flux to Radiant flux or power consumption, depending on context. |
| Luminous efficiency/ Luminous coefficient | V | 1 | |||
September 8, 2017