What Colour is this Shirt?

We all know that objects can appear to be different colours based on the light that is shining on them: an object that appears yellow in white light might appear either red or green if only red or green light was shining on it, for example, and so on..

But it's an issue that can be hard to demonstrate in a school lab where we may have access to various colour filters and ray-boxes, but where it's near impossible to get rid of the surrounding white light. And even if we manage to make it dark (and assuming we could trust our students if we did so!), the fact that filament bulbs generally emit a broad range of colours and that the filters often allow a surprising range of colours through, tends to complicate the situation and leads to unpredictable outcomes.

But my daughter got a set of LED lights for her room at Christmas that allow the user to vary the colour output with a remote control, and I've noticed that the effects on reflected light there can be quite dramatic. It's a room that can be made very dark for one thing, and of course the other issue is that the output created by LEDs tend to have quite a narrow frequency range - so the blue light is only blue, for example, and the red is only red etc.

I thought the effect of light reflected off her Cúl Camp shirt from a few years ago was particularly striking. And the remote control allows you to vary the output quite quickly, so I videoed it for a few seconds and put the result up here.

If you look at the Kellogg's logo in particular, the colour changes nearly every second.

In white light, the shirt looks like this. It was almost a national uniform for under 12s a few years ago, as the Cúl camp shirt has been every summer in recent years - until Covid. Hopefully we'll be seeing a new design this year!

these are the lights we used. ...

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