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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 Examples | 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.
See also: Apostilb, Lamberts Laws, Lumen.
  
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