LIGHTING (CONT) . Lighting Definitions
The Kelvin is the base unit of temperature named after the Belfast-born, Glasgow University engineer and physicist William Thomson, 1st Baron Kelvin (1824–1907), who wrote of the necessity for an absolute thermometric scale.
Kelvin temperature To specify the colour (spectral) output of a lamp we use colour temperaturemeasured in Kelvin (K). The warmer the colour the lower the colour temperature; candlelight can have a value as low as 1500K whereas outside daylight can have a value up to 10000K.
Luminous Flux Light output froma lamp (or point source) is measured in Lumens (lm). This indicates how intense the light is. The higher the value themore light is emitted. Lumens does not indicate the spectral (colour) output. Illuminance This defines how well lit a surface is and is measured in Lux (lx).For an inside space such as a room, the illuminance is the total amount of falling light and can include both natural and artificial light. This is themeasurement used to define recommended light levels in The recommended levels can range from20 to 5000lx depending on the function or the space. An operating theatre will require extremely high light levels, a car park facility on the other handmay not require as much. commercial, workplace and healthcare settings.
A high rating indicates that colours aremore authentically represented. Currently, eight pastel colour standards are used for tests when measuring the CRI score. Some critics argue that this test does not determine that accurate colour rendering and brighter standards such as R9 (a strong red) should be included. TheWell Building Standard (2019) indicates lighting should have a CRI R1-R8 value of 80 and above and an R9 value of 50 and above.
Luminaire A complete electric light unit.
Colour Rendering Index The CRI is a systemused tomeasure a light source’s ability to represent colour in comparison to a daylight standard. A light source is given a CRI rating (100 being the highest).
This illustration shows a range of colour temperature, measured in Kelvin - from 1000 to 10,000
The Colour Rendering Index
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