How we’re shedding new light on why, when it comes to matching colours perfectly, there’s no substitute for natural daylight.

Metamerism (illuminant metameric failure, actually) Rarely mentioned by name, but often a problem. Metamerism describes the effect whereby a colour can appear to change depending on the light source under which it is viewed and the material upon which it is reproduced. For example, imagine a paint sample in a swatch book. In daylight, when the paint is chosen, bought and painted on the wall it looks the same as on the printed swatch book. However, that evening, when the light source changes, the colour looks different in the swatch book compared to the paint on the wall: well, that’s matamerism.

Interesting but irrelevant? Perhaps. But in printing we’re often asked to approve images on press by comparing them to a proof (usually digital and on a different material to the printing paper). You may well be asked to view the proof and printed sheet in a viewing booth where fluorescent tubes are used to simulate a lighting condition (usually daylight).

This happened to me a couple of weeks ago and, on press, the image needed a lot less yellow ink in order to match the proof. I became suspicious because nothing else had been out of balance and anyway, I’m a suspicious sort of person. I was concerned that I was in the middle of an illuminant metameric failure. It was 11am and the sun was out so off we trooped to a viewing area nicely in the shade of the bins and sure enough, the image needed more yellow, not less, to match the proof. A complete reversal of the indoor plan (look in the shade, not direct sunlight).

Colour is a strongly subjective perception Obviously, I really appreciate the expense companies go to simulate daylight conditions but, if the sun’s out, you can’t really beat the real thing. And remember, the only lighting condition you can be certain you share with the client is real daylight.

This summer was a grim D50

Words: Francis Atterbury