Illuminance
This is defined as the luminous flux arriving at a surface that is perpendicular to it per unit area. The metric unit is the lumen m-2 or abbreviated to lux or lx.
In the British system this was defined as the lumen ft-2 or known as the foot candle or fc. 1 foot candle ~ 10.7639 lux
| Sunny day | 10000 lux |
| Overcast day | 1000 lux |
| Precision mechanical workshops, operating theatres | 1000 lux |
| Supermarkets, workshops | 750 lux |
| Normal office, library | 500 lux |
| Classes | 250 lux |
| Warehouses, home, theatre | 150 lux |
| Very dark day | 100 lux |
| Twilight | 10 lux |
| Full moon | 0.1 lux |
| Quarter moon | 0.01 lux |
| Starlight | 0.001 lux |
| Overcast night | 0.0001 lux |
For very detailed precision work the light level may need to be greater than 1500lux.
Photograph courtesy of industrial-needs.com
Note: It is very difficult to measure illuminance more accurately than ±10%.
See also: Apostilb, Foot Candle, Lamberts Laws, Lumen.
- Weblinks:
- PCE Group Your advisor in measuring and weighing proficient.