How to avoid color temperature inconsistencies.

Here at HitLights, we talk about color temperature and LEDs quite a lot. In the past we’ve discussed how to choose the correct one, and how there is no such thing as ‘the right’ color temperature. Today’s blog discusses the more technical aspects of colour temperature - and why two strips with the same temperature might not necessarily appear the same.

Color temperature does not measure color

Somewhat counter-intuitively, color temperature does not actually measure color. Per wikipedia, color temperature “is the temperature of an ideal black-body radiator that radiates light of a color comparable to that of the light source”.

In physics, a black-body radiator is actually exactly what it sounds like - a hypothetical black object that radiates heat and light solely due to the high temperature of the object (think something like a traditional incandescent light bulb). You’ll notice that the above description of a black-body radiator does not at all match the description of LEDs, which are neither black nor emit light as a result of high temperature. Herein lies the problem - LEDs are NOT black-body radiators.

“In practice, color temperature is meaningful only for light sources that do in fact correspond somewhat closely to the radiation of some black body, i.e., light in a range going from red to orange to yellow to white to blueish white; it does not make sense to speak of the color temperature of, e.g., a green or a purple light.”

- Wikipedia

LEDs are NOT black-body radiators

The use of color temperature to measure the ‘color’ of LEDs is a flawed usage of this measurement. Because LEDs are not black-body radiators, and because LEDs emit light beyond the traditional red-orange-yellow-white-blue color temperature spectrum, there is an inherent variability in the actual color of the light produced.


The diagram above shows the color of an ideal black-body radiator (in the curving line from bottom left to top right) bisected by lines representing various color temperatures. Where these lines intersect is the theoretical color for each temperature for an ideal black-body radiator. You’ll notice, however, that the colour temperature lines extend far to either side of the ideal black-body curve. While the math on these lines is solid, it should be noted that the further away you get from the black-body curve, the less meaningful these values are. The International Commission on Illumination puts it as below :

Although the CCT can be calculated for any chromaticity coordinate, the result is meaningful only if the light sources are nearly white.

What this means is that any light source of a given color temperature could fall anywhere along the line given in the above diagram - rather than on a single value. Incandescent light bulbs, which produce their light through thermal radiation (heat) correlate pretty closely with ideal black-body radiators. For these light sources, color temperature values are generally pretty reliable. For LEDs (and indeed other light sources such as fluorescents and halogens), they are less reliable - and can fall within a range. This means that if you have an existing light source of a specific color temperature, a new light source with the same color temperature is not guaranteed to match the original appearance.

What can you do?

First, if you’re purchasing high quality strips from a reputable manufacturer (say, premium strips from HitLights), you’re much more likely to get strips closer to the black-body color temperature. Lower quality strips from less reputable manufacturers are much more likely to technically meet color temperature requirements (to meet specifications) while making little attempt to meet the actual spirit of the measurement. This makes sense if all the manufacturer cares about is your bottom line - as the chips that are further away from the black-body line are less desirable, and therefore cheaper.

Second, if color matching is important, you might consider purchasing all of your products at the same time, and from the same batch. Even high quality strips have variations between batches, and there’s nothing worse than receiving a second strip that doesn’t match the first - and then discovering that the first batch has been sold through and is no longer available. This is an even bigger problem if your supplier does not have direct control of their inventory, for example at fulfilment centers of online marketplaces like amazon - where inventory ages, batches get mixed, and even two strips purchased at the same time may not match in appearance.

Third, if you must use two light sources of differing appearance, then you can minimize the effect of these differences by making smart design and installation choices. These color differences are less noticeable when the light sources are further apart, so choosing to install them on separate sides of a room, for example, can help. Differences are also more noticeable with a common reference. If the entire room is painted the same color, then the difference in color will also be more noticeable. While we’re not advocating for painting a room in two different colors, you can use areas of different color or material to break up these references - for example installing one light low near a dark floor one another high near a lighter ceiling.

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Got color temperature down? It's just one small factor in choosing the right LED light strip for your project - our free eBook, titled 'How to Choose LED Strip Lights' is an ideal guide in the next stage of your LED lighting journey.


 

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Further Reading

Color temperature is a highly technical subject, and this blog has barely scratched the surface of the topic. You can read more about color temperature at some of the sources below.

Wikipedia : Color Temperature
Wikipedia : Black-body Radiation
International Commission on Illumination (CIE)
HitLights Blog : Choosing the right color temperature
HitLights Blog : There is no such thing as the right color temperature