Colour consistency is a key quality for white lights, one that can either make or break a lighting project. That said, it is also one that’s overlooked often. Continue reading to find out what color consistency is and more importantly, how to attain great colour consistency every time.
What is Colour Consistency in Simple Terms?
Generally speaking, colour differences can be easily distinguished across two axes: blue/green and green/magenta. For instance, you might notice one light is more “green” in comparison to another or “bluer” compared to another.
It is possible to distinguish blue/yellow difference with the help of colour temperature, which is measured in Kelvin (k). The amount of colour variation that’s acceptable may vary from one application to the next, but when it comes warm white LED light, +/-75K is usually regarded as the threshold for distinguishable colour temperature. The threshold for cool white or normal white, on the other hand, is +/-150K.
Green/magenta variation, by contrast, can be distinguished using a metric that’s not as well known as Kelvin. The name of this metric is Duv. When the reading is 0.000 Duv, it indicates the light source is neutral. On the other hand, when Duv is in negative, it points toward a shift toward the magenta colour. Conversely, when Duv is in positive, it shows a green colour shift. Generally speaking, we are able to notice Duv values that have a variation of over 0.002.
Remember that Duv variation, for some reasons, is frequently overlooked, even when, compared to CCT variation, it is more noticeable. In case colour consistency is a make-or-break quality for your application, don’t forget to ask the supplier to provide Duv tolerance metrics.
What is SDCM or MacAdam Ellipses?
SDCM stands for Standard Deviation Colour Matching. Some manufacturers prefer to describe colour consistency using a different metric — SDCM or MacAdam ellipses. Both these terms refer to the same metric and concept. The unit of measure, in this case, is “step.” The greater the number of steps, the bigger the colour variation.
In the case of standard applications, a 5-step SDCM is regarded as an acceptable color consistency. By contrast, for demanding applications, the threshold is generally 3-step SDCM. It is possible in some instances even lower color consistencies are required. However, the majority of people are likely unable to identify colour deviation once the consistency is as low as 1 SDCM or 2 SDCM.
So which metric is superior — CCT, Duv, or SDCM?
SDCM is considered superior than Duv and CCT mainly due to two reasons. One, it is able to capture the variation in not only blue/yellow direction but also in green/magenta and distill that that in a single number. That can prove useful since in a small number of cases colour deviations occur not in one dimension but rather in both. Two, a 100K variation considered bigger at low colour temperatures. The impressive thing about SDCM is that it takes this fact into consideration and makes all required adjustments as per the colour temperature. The main drawback is that more than a few manufacturers are still not adequately concerned with colour difference and so are likely to be not familiar with this particular metric.
How do colour consistency problems become noticeable?
There are two sorts of colour consistency issues with LED lights:
Colour mismatch in a single LED strip segment or reel
- Colour mismatch between two or more LED strip segments or reel
When the colour variation between individual LED bulbs within a single LED strip is too much, you may notice the first inconsistency. This generally happens due to the inadequate tolerance specification from the manufacturer.
In case of other lights, it is the second type of mismatch that is more apparent and common. This generally occurs due to the variations occurring between manufacturers or batches.
You can avoid the second kind of inconsistency by using the LED lights of the same batch in one installation, especially if they will be seen together.