Lighting terminology

Ambient Light – Blanket light level or general Illumination that comes from all directions in a room that has no visible source.

Brightness – is what the eye detects and the brain interprets as light thus affecting the size of your iris.

Colour appearance – The apparent colour emitted by a light source, measured by correlated colour and described as warm, intermediate, cool or cold.

Colour Temperature – Measured in Kelvin, this is a characteristic of visible light that has important applications in lighting, photography, videography, publishing, manufacturing, astrophysics and other fields. In the lighting industry we use 2700K Warm white, 3000K White, 4000K Cool White or 6000K Daylight.

Colour rendering – The ability of the light from the light source to reveal the colours of an object. It is determined by the spectrum of the light source. Measured by colour rendering index (Ra) and the higher the number the better, up to a maximum of Ra = 100. LED’s normally have a Ra 80 / 85 but can now be supplied with a Ra 95 at a cost.

Contrast – subjective experience of comparative brightness between areas of lluminance seen simultaneously. The difference between light and dark.

Glare – UGR The discomfort or impairment of vision experienced when there is excessive contrast in the field of vision.

Illuminance – The amount of light falling on an area divided by the size of that area. (also known as the “density of the light”) measured in lux, varies from 0.2 lux by moonlight to 500 lux for office lighting to 100,000 lux by bright summer sunlight.

Luminance – The measured brightness of a luminous or illuminated surface. Measured in cd/m².

Lux – is the SI unit of illuminance and luminous emittance, measuring luminous flux per unit area. It is equal to one lumen per square metre.

Lumen – a measure of the total “amount” of visible light emitted by a source AKA luminous flux.

Luminous efficacy – The ratio between the luminous flux or Lux emitted by a light source to the power consumed by the source. This is important to the industry and measured in terms of lumens per watt (lm/W) for Part L compliance.

LOR – Light output ratio is a measurement published by lighting manufactures to show the final amount of emitted light from the luminaire.  This is key and the responsibility of a competent designer to check for Part L compliance and other standard governing bodies.

Luminous flux – The rate light is emitted by a light source measured in lm known as Lumens.

Luminous intensity – The amount of luminous flux radiated in a particular direction, measured in cd or lm depending on the light spectrum.

Task Lighting – to increase illuminance of a local and defined area for reading, theatre or desk works.

Uniformity – The ratio of the minimum illuminance to the average illuminance over a specified area.

Switching – Reference to the type of control to lighting powered by a circuit.

Dimming – adjustable light output from 0% to 100%.

Chromaticity – of an LED product – that is, degree of deviation of its colour temperature – is defined in MacAdam ellipses in Standard Deviation of Colour Matching (SDCM) as per the CIE 1964 standard. The MacAdam system originates from the United States and ranks colour quality on a scale of 0 to 10.

MacAdam  1 to 3 step – Macadam 2 SDCM: museum, gallery application Macadam 3 SDCM: office, school, retail, healthcare applications. Divation from a chromatic diagram steps 1 to 3 is not noticable by the un-trained eye.

MacAdam  – Macadam 3 SDCM: outdoor facade / Macadam 5 SDCM: other outdoor applications. 5 step is noticable but for outdoor apllications it fine unless you want to illuminate a white wall. Mcadam step 4 is quite often a fluorecent lamp.

Please contact Stuart Moth to arrange a presentation to educate your staff on the lighting basics.


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