Figure 5.51. Light level standards

The accurate calculation of illuminance (the level of light) is a specialized skill. This section does not attempt to explain this science but gives a basic background of the principals involved. Illuminance is the luminous flux density at a surface expressed as lumens per square meter (lm/m2) or lux. The light of the full moon may give approximately 0.1 lux and a bright daytime sky 30,000 lux. For classrooms, suitable illumination levels are between 300 to 500 lux at the working plane. Good illumination is most important at desktop height. Illumination levels for most school spaces are assessed at a working plane about 800 mm above floor (700 mm for desks and 850 mm for benches)

The daylight factor, which is the percentage of the illuminance outdoors received at a point indoors, has three components: