Does Silver Reflect Heat in the Dark?
Discussion
MiniMan64 said:
Silver is a poor emitter of thermal energy so maybe that?
Or do you mean on the inside of the bag? Because in that visible light has nothing to do with it…
Yes - inside the bag once closed.Or do you mean on the inside of the bag? Because in that visible light has nothing to do with it…
Edited to add, when I search on-line I get stuff related to heat but about colours absorbing light. In a closed bag there might still be some light but not much at all. Especially if the bag is made specifically to contain heat.
Edited by Randy Winkman on Wednesday 30th November 08:56
There's 3 main ways heat moves around; Radiation, Conduction and Convection
The foil doesn't just reflect light but also reflects infrared radiation given off by hot items. The box is insulated to stop heat being conducted through it, and closed to precent convection (air warmed by the food expands so would rise and be replaced by cold air if not sealed)
The foil doesn't just reflect light but also reflects infrared radiation given off by hot items. The box is insulated to stop heat being conducted through it, and closed to precent convection (air warmed by the food expands so would rise and be replaced by cold air if not sealed)
ZedLeg said:
Randy Winkman said:
Cheers. I'm still not sure why the colour matters?
The absorption/reflection properties of the material doesn’t change based on whether it’s in full spectrum light or not. Maybe we just assume that because silver reflects light, it also reflects heat. However, visible light and IR are next to each other in the EMS so perhaps there's some crossover. But that doesn't help the OP. And would it be different on a conveyor belt...?
Do you mean "re-emit" rather than reflect?
If the silver is "in the dark" then there cannot be a source of light which would be the basis of the reflection.
The answer is, of course silver can re-emit because it will absorb some energy when it is exposed to a light source and later, when the light source is gone, some of that energy will be re-emitted as infra-red.
If the silver is "in the dark" then there cannot be a source of light which would be the basis of the reflection.
The answer is, of course silver can re-emit because it will absorb some energy when it is exposed to a light source and later, when the light source is gone, some of that energy will be re-emitted as infra-red.
Eric Mc said:
If the silver is "in the dark" then there cannot be a source of light which would be the basis of the reflection.
Surely the point is it's not in the dark across the whole spectrum. Visible light is 0.4 to 0.7 micrometers, but hot stuff will be emitting infrared somewhere in the 1-100 micrometer range, which is still going to be reflected by aluminium foil better than it reflects visible light.Google the concept of "black body emitter" - essentially the opposite of silver foil.
amongst the crazy things in life is central heating radiators being painted white. It suppresses their ability to radiate heat.
As regards the use of silver foil the "colour" isn't really relevant at all. What matters is "reflection". For instance, when you look at yourself in a mirror you don't see the mirror you see your perfect reflection with no colour changes.
(How come the reflection is swapped left to right but not upside down....?)
amongst the crazy things in life is central heating radiators being painted white. It suppresses their ability to radiate heat.
As regards the use of silver foil the "colour" isn't really relevant at all. What matters is "reflection". For instance, when you look at yourself in a mirror you don't see the mirror you see your perfect reflection with no colour changes.
(How come the reflection is swapped left to right but not upside down....?)
Randy Winkman said:
MiniMan64 said:
Silver is a poor emitter of thermal energy so maybe that?
Or do you mean on the inside of the bag? Because in that visible light has nothing to do with it…
Yes - inside the bag once closed.Or do you mean on the inside of the bag? Because in that visible light has nothing to do with it…
Edited to add, when I search on-line I get stuff related to heat but about colours absorbing light. In a closed bag there might still be some light but not much at all. Especially if the bag is made specifically to contain heat.
Edited by Randy Winkman on Wednesday 30th November 08:56
Simpo Two said:
ZedLeg said:
Randy Winkman said:
Cheers. I'm still not sure why the colour matters?
The absorption/reflection properties of the material doesn’t change based on whether it’s in full spectrum light or not. Maybe we just assume that because silver reflects light, it also reflects heat. However, visible light and IR are next to each other in the EMS so perhaps there's some crossover. But that doesn't help the OP. And would it be different on a conveyor belt...?
Even the finish of the material can effect it. The shiny side of kitchen foil reflects more radiation than the matt side.
ZedLeg said:
No because the colour is relevant. The absorption properties of the material are what makes it appear a certain colour, so if you lined the bag with a black insulated material it still wouldn't be as efficient as the silver coating as it's absorbing all radiation rather than reflecting most of it back into the space.
That's very true. But silver isn't actually a colour... 
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