# Colours in winter camouflage, and thermal aspects

When I was 12 or 13, I read somewhere that the colour black absorbs all light, and therefore gets warmer than clothes of other colour. This fit well in with what I had observed myself.

A year or so later, we did colours and light in physics class. For whatever reason, the teacher ended up asking me (I suppose I must have made the claim that winter clothes should be black to be warmer, or something similar) if there was any reason for soldiers in snowy environs, other than camouflage, to wear white. I categorically said no. He asked again, hinting at an answer other than mine. He didn’t give one, though.

So, here’s my question for you: Is there any reason, other than camouflage, for soldiers in snowy environs to wear white?

Black clothing loses heat more quickly in the same way it absorbs it more quickly, IIRC. Thus, (presumably), white clothing retains heat longer.

Is that not reason enough? You can always wear more layers.

>Black clothing loses heat more quickly in the same way it absorbs it more quickly, IIRC.

Really, this really isn’t exactly right. Sunlight, and any light we see by, has a wavelength around 1/3 or 2/3 or so of a micrometer. Objects that are hot enough, like a lamp filament, radiate heat at wavelengths like this too. But objects that are at ourdoor temperatures only do their radiating at longer wavelengths, maybe 10 micrometers or so. Therefore, visibly black surfaces will do a good job of absorbing light and turning it to heat, but how they radiate heat away depends on how “black” they are at longer wavelengths. Some things are black at both visible and “thermal ir” wavelengths, like electrical tape. But many things are very different. For example, human skin can be very dark to very light in the visible, but it is almost perfectly black at wavelengths near 10 um.

Afraid no answer to the OP is popping up for me, tho.

So the type of dye would determine the amount of heat radiated? Or the material?

Well, that’s what I was thinking, but the teacher seemed to hint at there being something more to it, that white was chosen not only for camouflage. It should be said that this was some 17-18 years ago, so my memory may well be a bit off.

What little physics I have picked up tells me that this is the case. How much heat is lost by radiation out is determined by the material, whereas how much of the solar radiation is converted to heat depends to a large extent on the colour.

By type of dye I mean the specific composition of the dye or whatever coloring agent is used, rather than the color; I’m asking Napier what determines the “blackness” of the item at other wavelengths, as he put it.

Qualitatively, the same things that determine blackness at any other wavelength. Every material has some wavelengths that it absorbs more efficiently than others. How much of various visible wavelengths a material absorbs determines the color that we see (though not in a one-to-one manner), but it also has “color” in parts of the spectrum we can’t see.

To the extent that this matters for winter clothing, the ideal winter coat would be black in the visible and possibly near infrared (the wavelengths where sunlight is strongest), but white in the far infrared (the wavelengths where an object at around human body temperature radiates most strongly). In practice, though, the amount of down, wool, or other insulating material is going to be a lot more important.

Ummm… it’s easier to tell if they’ve been wounded somewhere because the blood shows up better?
Other than that, I got nothin’. And certainly no physics-based reason.

Is that a good thing?
I’m pretty sure the primary consideration for selecting the color of a military uniform is it’s ability to conceal the wearer.

The purpose of a coat is to preserve your body warmth, not to absorb heat from the sun to warm you up. The same insulation that keeps your interior warmth in, would also serve to keep an exterior warmth out.

The problem with dark color coats is that the exterior shell may absorb heat from the sun and become much warmer than ambient. Having a warm outer shell causes snow on the coat to melt and wet the insulation, thereby causing it to be less effective at preserving your body warmth.

You don’t have to sort laundry between whites and colors?

Thanks, that’s a great answer. Though I’m a bit perturbed I didn’t think of it myself. I’ve had 17 years, dammit.

I somewhat frequently work with near-ir cameras and so far all the visibly black clothing I’ve seen was light grey in this spectrum (>800nm).