Why are highlighters so bright?

09 October 2018

highlighters

highlighters

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Question

Why are highlighters so bright? How do they work?

Answer

Listener Cam highlighted this issue for us, Chris Smith put it to physicist Jess Wade from Imperial College London.

Jess - This is a really great question. I think we’re familiar with most chemicals are colourful because they absorb some colours of light and not others. But in highlighters there are special dyes that particularly absorb the kind of ultraviolet part of the spectrum. And they do that because they’ve got a bunch of atoms in there that have alternating single and double bonds and we call those things conjugated.

They’re exactly like all the materials I work on actually. And these dyes that absorb in the UV part of the spectrum, sometimes those electrons absorb that kind of light, jump up just like the lasers we were talking about before, and then really quickly aren’t very happy up there and jump down and fluoresce.

The highlighters actually contain a small amount of these fluorescent dyes and you can get these fluorescent dyes in all different colours which gives us all the different colours of highlighters.

Chris - Which is very nice indeed.

Jess - Beautiful.

Chris - Science in action. Thanks very much Jess. Not you, the highlighters. But you’re science in action as well.

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