LED FAQs (Part 5): CCT

In this series, we discuss some of the most frequently asked questions we receive about LEDs. Today, Color Technology Specialist Wendy Luedtke introduces CCT and D_uv and what they mean in the world of LED fixtures.

Ready to get fancy? As I mentioned in my earlier post, if a light source does not plot exactly on the blackbody curve, a perpendicular line is drawn from the source’s chromaticity coordinates through the blackbody curve. Where they intersect is the correlated color temperature, abbreviated CCT. Here’s the example I gave in the third installment.

In reality, the light emitted by many luminaires doesn’t plot directly on the blackbody. It plots a little above or below. Because that difference can be visually apparent, it’s important to look at D_uv values for any sources not plotting on the blackbody curve. While two sources could technically both be 3500 K, for example, one might be a little pinky warm white while the other might be kind of yellowy/greenish warm white. It may not matter, but if the two sources will be used next to each other, that difference may be very apparent.

Looking at light from a 4100 K source with a positive D_uv all by itself, it will likely appear neutral white. Here’s an example of what it might look like:

Repeat that with a 4100 K source with a negative D_uv and it, too, will likely appear neutral white:

However, side by side, they may look yellow/green and pink:

Not pretty, is it? That’s why we need to pay attention to D_uv values. Up next: ANSI C78.377!