Don't CRI

The overlooked importance of light quality in design
Eric Goodwin

Not all light is equal, some light is much better than others - and it’s an important distinction when talking about design.

As we learn in science class, white light is made up of all the colours in the rainbow, demonstrated by using a prism to split ordinary white light into a rainbow - but in reality this is a bit of an elementary way of looking at it (pun intended). This is because while yes, white light is made up of all the colours in the spectrum, white light can be composed of varying quantities of the different colours in the spectrum - and can even skip certain colours all together.

Think of it as if you had tubes of paint in all the colours in the rainbow, and you wanted to make the colour brown. There are a ton of different ways you could mix different coloured paint together to get brown, and the same is true with light.

This means that light may look white, but it could be missing certain colours in the spectrum or have an overabundance of certain colours.

The quality of light has a handy measurement though - CRI which stands for Color Rendering Index. This is a handy tool to gauge the quality of light, even if it looks white.

CRI is measured as a score out of a possible 100, with certain light sources measuring at a full 100 - as in they have all the colours in the correct quantities within the white light, or rather perfect colour rendition. Sunlight, incandescent light bulbs, and halogen light bulbs all score a CRI of 100 and have perfect colour rendition.

  • Side Note: We won’t dive too deep here because CRI actually isn’t a perfect measurement. Incandescent light has a 100 CRI but because it has a low kelvin temperature (2700K) its wavelengths have been pushed to the red side meaning it has less purple, blue, and green wavelengths within it.

The issue is that even though incandescent and halogen light are very high quality they also have drawbacks, namely they produce a lot of heat and consume a lot of energy. So new lighting technologies have popped up, namely fluorescent and LED light.

Have you ever been in a bathroom lit by a fluorescent light and thought you looked horrible? This is because fluorescent lights produce a lot of green and blue light in their wavelengths but have trouble producing oranges and reds, and your skin is mostly made up of varying shades of orange and red.

LED’s have come a long way in recent years, but they still aren’t perfect. Even LED lights from large reputable manufacturers boasting high CRI numbers aren’t as good as you might think.

Here’s a test we did recently:

The top image is lit by a 60W incandescent bulb, and the bottom image is lit by a 60W equivalent 2700K LED bulb (from a big name manufacturer) with a 90CRI rating! All the camera settings were exactly the same.

But here’s the tricky part, human eyes.

When I swapped the light bulbs I could tell the LED looked a little different and at the time I thought it looked fine and not a super noticeable difference. Once I brought the two images up on the laptop screen though I was blown away, I mean in that second image I look like I’m in The Matrix!

This is because human eyes have a sort of auto white balance (well kind of auto everything really). Our eyes are constantly adjusting to different light levels and colours very quickly, so in real life we don’t really notice light changes like the changes noted in the photos above.

So if our eyes have auto white balance, who cares right? Well the thing is that even though your eyes are adjusting to the light, the light is still lacking certain wavelengths. In those images above you can see that there is way less red and orange in the LED light and contains way too much green.

Now this whole topic is very important for cinematographers and photographers, especially when dealing with skin tones, but it’s important for designers as well. As designers, colour is very important - especially if you are working with fabric. Think of how different a red fabric would look under those two lights.

So when setting up your design area, consider not just the lighting, but the light quality. It makes a bigger difference than you might think.