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Pick a colour temperature, any colour temperature....

As each week goes by, more lamps and fittings of various flavours join the market - LED, compact fluorescent, metal halide, tungsten-halogen, incandescent - all sources with different properties.

The most noticeable, though (one would have thought) is the colour temperature. Colour temperature refers to a measure of how warm or cool a light source appears to us (if you're really interested, the science bit is here on Wikipedia). Mixing lamps of different colour temperature together in the same space is uncomfortable to the eye, and makes it impossible to render colours accurately within the area.

When virtually all lamps were incandescent, colour temperature was rarely a thought when purchasing lamps for general use. For general lighting purposes, there are two or three notional tones of white light available to the consumer - warm white, cool white, and sometimes daylight. There are pros and cons to all of these, and the final choice will likely be informed by a variety of factors. That said, though, when it comes to lighting your interior areas, unless you really are defining a highlight, pick a colour temperature that's right for your building, stick to it, and use it to inform other lamp or fitting purchasing decisions.

While LUX Magazine cautions manufacturers regarding over-exuberant lifetime claims, it is nevertheless true that any lamp or fitting purchased now will more than likely last you a very long time. It is therefore imperative that your colour temperature strategy is planned ahead, and robustly stuck to - if need be as part of your corporate design scheme and laid down on paper.

You'll need to do some playing. Colour temperature is measured (scientifically) in degrees Kelvin (the higher the colour temperature, the cooler the light - see left), but manufacturers often prefer words. The term 'warm white' is generally assumed to be equivalent to the warm yellowy glow of tungsten that we are so used to. That is equivalent to around 2700K, although one leading manufacturer rates some of their 'warm white' lamps at 2800K - and this difference is perceivable. 'Cool white' lamps operate in the region of 4000K, while true daylight is to be found at about 5000K.

The other key indicator to look out for is the colour rendering index (CRI). This measures how close to perfect a lamp can get colours to look - the theoretical best would be 100. Compact fluorescent lamps have a CRI of about 80, while good quality LED lamps will be greater than 80 - even as high as 95. You'll often not find the CRI information on the packet or online - you'll have to go to the manufacturer's catalogue.

For entertainment and hospitality purposes, it is usually desirable to go with a warm light, as it promotes an atmosphere of intimacy and comfort conducive to social interaction. Any random lamp or fitting that is the 'wrong' sort will stand out like a sore thumb, and puncture the feel of a room - cool lamps used in a predominantly warm room look cheap and industrial, while warm lamps in a cool room look dirty. Using cool lamps in richly upholstered areas will look odd, although the opposite is not true.

The issue is at its height in heritage spaces. While there can be planning protection for even some fittings within a historic space, there is no such protection for the colour of the installed or historically intended source. Perceived economies can then lead to low quality, low CRI lamps of inappropriate colour temperature in some of our most valuable spaces, inadvertently despoiling them, potentially for many years to come.

The key message, therefore, bears repeating here - choose your colour temperature wisely - you're probably going to be using it for a long time, and as you know, you never get a second chance to make a first impression.

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Graphic - Samsung

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Tags: cfl, color, colour, colour temperature, cri, heritage, index, led, rendering, retrofit, More…temperature, tungsten

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Comment by Tim Atkinson on July 17, 2013 at 10:53


You're absolutely correct, and I was a little disingenuous implying that CFLs never have good colour rendition - some can be very good.

The Kruithof curve (Wikipedia entry here) does need to be taken account of (and indeed should be!), especially in large spaces such office floor slabs, shopping centres, airports, etc.

An issue we have in the public areas of entertainment venues, for example auditoria of theatres or pub saloons - even large ones relatively speaking) is that the intimate feeling expected by patrons is rarely delivered by higher colour temperature. That said, in the grand scheme of buildings, these are still small spaces/areas, so I should (unscientifically) imagine have the effect of dampening the Kruithof curve effect.

Comment by Steve Hayes on July 16, 2013 at 11:29

You need to take account of the  Kruithof curve, the brighter the lit space the higher colour temperature that "seems right"

It's not true that CFLs and linear fluo lamps never have good CRI.  As a generalisation, most LED lamps have poor CRI (60odd), bog standard fluo lamps reach 80 something, any decent fluo lamp supplier can come up with CRI90+ up to CRI98 fluo if you ask nicely; still the best fluo lamps have better CRI than LED, but that's changing.