LIET6 Colour Data
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CRI
Colour Rendering Index (CRI) is a quantitative measure of the ability of a light source to reproduce the colours of various objects in comparison with an ideal or natural light source. Light sources with a high CRI are generally most desirable. The CRI is calculated by comparing the colour rendering of the test source to that of a “perfect” source, which is a black body radiator (basically a block of iron) for sources with colour temperatures under 5000 K.
CRI by itself does not indicate what the colour temperature of the reference light source is however; therefore, it is necessary to also cite the correlated colour temperature (cct). The cct is the temperature of the Planckian radiator whose perceived colour most closely resembles that of a given black body radiator stimulus at the same brightness and under specified viewing conditions. The Planckian locus is the path that the colour of an incandescent black body would take in a particular chromaticity space as the blackbody temperature changes (i.e. as the temperature of the black radiator increases so will its colour temperature), it goes from deep red at low temperatures through orange, yellowish white, white, and finally bluish white at very high temperatures. An example of a practical black body radiator is a tungsten filament bulb, which actually produces it’s light by heating the wire to a given temperature, hence the colour temperature is the temperature of the wire.
CRI is not the most realistic way of measuring modern lighting sources such as LED's. A ‘perfect’ light was considered an incandescent bulb back in the early 1930’s. Until a more modern way of measuring light is standardised, LED lighting will always appear less than ‘perfect’ with respect to historical CRI ratings. In practice however, in many cases LED lighting will render and illuminate better than many conventional light sources.
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Colour Spectrum and CRI
The broader the spectrum of colour there is in a light source the better. The human eye can only see colour that is being emitted or reflected from a light source or surface. If a light source does not contain the full colour spectrum then human eyes simply will not see all of the colours in the spectrum. A good example is a low-pressure sodium street light, with a very low CRI of between zero and one, predominantly emits a dull yellow light and limits an individual’s capacity to accurately distinguish between colours; a red or green car for example will appear to be a dark colour but the actual colour will be impossible to determine.
A compact fluorescent light has an inaccurately high CRI rating due to the positioning of the colour spikes, which has been deliberately engineered to attain a high rating. Colour wavelengths in the spaces between the spikes will be indistinguishable. In Halogen lights there is very little blue and green, mostly red and masses of infrared (heat). Much of the Halogen’s light output therefore is not seen. |
Illustrating the spectral plots of CFL, Halogen, and LIET. Notice how LIET with a filter
perfectly contains a natural spread of all visible light and contains virtually no I.R.
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Beam Angle - General Term |
| Clear Lens |
60° to 10%* |
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* From a 2.1 meter height, there is a 2.1 meter spread of light of which 90% of the light is within 2 meters. |
| Diffusing Lens |
180° |
| Clear Lens |
52° to 50% |
| Lens Aperture Diameter |
69mm - 2.71 inches |
| CRI |
63 - 83 |
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CRI is not the most realistic way of measuring modern lighting sources such as LED's. A ‘perfect’ light was considered an incandescent bulb back in the early 1930’s. Until a more modern way of measuring light is standardised, LED lighting will always appear less than ‘perfect’ with a CRI rating. |
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Peak Lux from 2.1 meter height |
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Warm White |
Bright White |
Cool White |
| No Lens |
130 Lux |
150 Lux |
150 Lux |
| Clear |
121 Lux |
136 Lux |
136 Lux |
| Rose |
105 Lux |
117 Lux |
117 Lux |
| Pink |
97 Lux |
106 Lux |
106 Lux |
| Honey |
111 Lux |
126 Lux |
126 Lux |
| Amber |
105 Lux |
116 Lux |
116 Lux |
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