Why do embers glow red?

12 January 2016


A fire burning



Why do embers in a wood fire glow red?


Kat Arney put this burning problem to physicist Stuart Higgins...

Stuart - If you think about what's happening there - so you've got a lot of heat, and you've got everything that's warm gives off thermal radiation and this is caused by all the electrons whizzing around in the materials and the molecules of the wood and they're giving off this thermal radiation. Now humans do this all the time.

We do this at room temperature but we can't see it, it's in the infrared. So if you ever see one of those infrared cameras, and you look at someone and they wave and you can see their hands, you can see the hot parts of them giving off this radiation.

Kat - But we don't see that, so why do we see it coming off fire embers?

Stuart - So, in this case, the fire is a lot warmer. It's giving off a lot more energy and, in that case the photons, the radiation that's been given off is of a higher energy and it shifts from the infrared, the bellow red, into the red region of the spectrum, so we can start to see if with our own eyes.

Kat - So if humans were as hot as a fire, we would glow red?

Stuart - Yes, yes we would!


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