Re: Blacker than Black

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Emission and absorption are basically the same process in reverse. 
The material properties determine how efficient the material is at
absorbing light - with the remainder being reflected. 

In the reverse process it determines how much energy is emitted as light
and how much is retained internally.

Hope this makes sense.

Derk

Sent from my HTC

----- Reply message -----
From: "K.H.Ranitzsch" <kh.ranitzsch@t-online.de>
Date: Fri, Nov 11, 2011 7:03 am
Subject: Blacker than Black
To: <gzg@firedrake.org>

Tom B schrieb:
> 
> TB: Admittedly, I'm confused now. It is 98% absorptive in infra-red,
> but it also radiates away more heat... I can't quite reconcile this in
> my head.

Indeed, this seems like a paradox, but actually, it's true.

It may help to think about it as two different processes. One is how the

surface handles incoming radiation, the other is how it sends radiation 
generated by the object.

When we call an object black or white, we refer to the way it handles 
incoming radiation. A white object reflects radiation, a black one 
absorbs it. Note: of course this also depends on the incoming light. At 
night everything looks black, because there is no light around.

Any object above absolute zero temperature also sends out heat 
radiation. It is in the infrared at normal temperatures, but if you heat

it up, it starts to glow in visible light.

By a paradoxic-seeming twist of the laws of physic, a black object is 
both the best absorber of incoming radiation and the most efficiet 
emitter of outgoing heat radiation.

I hope this helps
Greetings
Karl Heinz