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SECTION 1 - TERMINOLOGY
There are a number of key terms used that need to be further explained to assist in understanding the control approaches suggested.
Light
(or luminous flux) is electromagnetic radiation visible to the eye and is measured in lumens (lm)
Efficiency
of a light is measured in lumens per watt (lm/W)
Illuminance
is a measure of the amount of light falling on a surface and is measured in lumens per square metre or lux. The illuminance of direct sunlight is around 100,000 lux, normal daylight is 5,000 to 10,000 lux and moonlight around 0.25 lux.
Luminance
the eye sees the light radiating or reflecting from an object which is term ed the luminance and is measured in candelas per square metre (cd/m2)
Intensity
or luminous intensity is the strength of the light in a given direction and is measured in candela (cd)
Glare
uncomfortable brightness of a light source when viewed against a darker background. The luminous intensity gives an indication of the elvel of glare likely
Trespass
best measured by illuminance in the vertical plane of a window or building boundary
The relationship between some of these terms is shown in Figure A2.1 below.
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