Color consistency in lighting products

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For white LED lights, color consistency can be a critical but often overlooked quality that can make or break a project. Read on to learn how and why color variation exists, and how to ensure you can attain excellent color consistency for your LED light project!

What exactly is color consistency?

In general, color differences can be characterized across two axes - blue/yellow and green/magenta. For example, you may find that one light is "bluer" than the other, or more "green" than the other.

The blue/yellow difference can be characterized using color temperature (in degrees Kelvin). Acceptable color variation depends on the application, but for warm white, +/-75K is typically the threshold of noticeable color difference, and +/-150K for normal white or cool white.

Green/magenta variation can be described using a lesser known metric called Duv. A Duv of 0.000 indicates a light source that is neutral. A negative Duv indicates a magenta color shift, while a positive Duv indicates a green color shift. Typically Duv values that differ by more than 0.002 are noticeable.

Keep in mind that Duv variation is very much overlooked as a metric but is arguably more noticeable than CCT variation. If color consistency is critical for your application, be sure to ask your supplier for Duv tolerance metrics.

Standard Deviation Color Matching (SDCM) or MacAdam Ellipses

Some sophisticated manufacturers will describe their color consistency using a metric called SDCM or MacAdam ellipses, both of which refer to the same concept and metric. The unit of measure is a "step" and the larger the number of steps, the larger the variation in color.

In general, color consistency is deemed acceptable when it is within a 5-step SDCM range for standard applications, and 3-step SDCM range for more demanding applications for professional or architectural uses. In some cases, even narrower color tolerances are needed, but most people will not be able to tell that there is any color deviation once consistency reaches 1 or 2 SDCM.

SDCM is a superior metric compared to CCT and Duv for two reasons. First, it captures the variation in both the blue/yellow direction and green/magenta direction and distills it into a single number. This can be useful because in some cases the color inconsistency can occur in both dimensions. The second reason is that a 100K color difference is considered larger at lower color temperatures. SDCM algorithmically takes this into account and makes the necessary adjustments depending on the color temperature. The primary disadvantage is that many manufacturers are not sufficiently concerned about color difference and will oftentimes be unfamiliar with this metric.

How color consistency issues become apparent

With LED lights, the two types of color consistency problems are:

(1) color mismatch within a single LED strip reel or segment, and

(2) color mismatch between LED strip reels or segments.

The first type of inconsistency may occur if the individual LEDs on a single LED strip have too much color variation, and is typically caused by insufficient tolerance specification at the manufacturer.

For other types of lights, generally the second type of color mismatch is more common and apparent.

The second type of inconsistency, on the other hand, is caused by variations that may occur between batches or manufacturer. This may be due to chromaticity bin selection, or simply color measurement equipment calibration variations.

With the second type of inconsistency, you may need to be careful about placing two LED lights from different batches or manufacturers in the same installation, particularly if they can be seen simultaneously (e.g. in the same room). It is therefore important to keep track of information about each batch to ensure that this is consistent.

Another factor to be aware of is consistency in color shift. Unfortunately, LEDs shift in color over time due to degradation in phosphor or packaging materials, and this is an inevitable aspect of LED lights maintenance that should be considered.

Generally, LEDs from the same manufacturer and batch will shift in color at the same speed and direction. Therefore if a single LED light installation utilizes LED lights from a single batch and installed at the same time, there should not be any issues.

However, keep in mind that if you decide to add or replace an LED light after some time (e.g after a year of continuous use), even an LED light from the same batch that has not yet been used may exhibit color differences.

Similarly, even if you can verify that two LED light products are a visual match today, this does not guarantee that the color will change in the same way over time, such that in one years' time you may have color mismatch issues.

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