LED Lamps: All the Stats: CRI, FSI and Colour Temperature

There's no denying that it's taken us a little while, but we've finally got there.  We're pleased to announce that we've now added results for CRI, FSCI and colour temperature to our LED lamp results.

To get this far, we've had to combine several software tools.  As well as Colorfacts, which produces excellent graphs illustrating how much of the visible spectrum a lamp covers, we've also added Argyll CMS to our toolkit.  The former uses data from the visual spectrum to calculate the Colour Rendering Index (CRI) and the colour temperature.  This gives us a chance to thank everybody who has contributed to this free software, and its original author, Graeme Gill.  Argyll CMS allows you to measure the amount of UV in a flow of light, an area that we need to do a little more work on before we give the results.

Alongside that, we also take data from the visual spectrum and use a script produced by the Lighting Research Center to calculate the FSI.

What are the CRI, the FSI and what do the results mean?

The CRI is the Colour Rendering Index, and is a measure of how well a lamp can reproduce the colours in an object compared to a standard source.  The results go from 0 to 100, and the higher it is, the better.

The FSI is the Full Spectrum Index is a mathematical calculation of the difference between the spectrum covered by a light source compared to an idealised equal-energy spectrum.  There are more details on the website of the Lighting Research Centre.  To convert the FSI into a score that can be compared to the IRC, it's scaled up to a score out of 100, and given the name FSCI.  Again, the higher the result, the better.

Colour temperature is a slightly counter-intuitive concept.  The lower the value (and the colder the temperature), the warmer the light will look.  A bulb with a colour temperature of 2700 K will have an orange/red tinge (like the Econergyworld 8 W globe for instance).  Closer to 5500 K, the light is cooler and more like pure white, before gaining a blue or purple tinge as the temperature rises.  You can follow the colour temperature as the black line across the CIE colour space.


Now that our test procedure is firmly established and thoroughly bedded-in, we are going to go back through all of our light bulb tests so far.

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