To make the experiment a little more fun, let's further assume that the curtain consists of a 1 mm thick layer of flexible woven copper behind the thin almost transparent white linen layer (which is an isolator like most textiles).
Observation: When there is a white linen curtain at a window, its colour guarantees that sun beams (and thereby heat) are reflected pretty well.
In contrast to that, if you spray the white linen with a thin layer of let's say black paint, sun beams and thereby heat is collected pretty well, heating up the room.
Conclusion: A thin layer of dark material at a surface is sufficient to change the heat behaviour of a much bigger voluminous body below:
This indicates that the relevant physical processes of turning sun beams into heat take place at the surface of (such) materials.
Since the sun beams are not powerful enough - as far as I know - to change the core of an atom, it seems obvious that the excitation and electron recombination are changed by dark surfaces in a way that let's the resulting electro-magnetic waves not turn into light beams that move away from the surface again (i.e. are reflected) but instead let electro-magnetic waves change their wave length and frequency in a way that turns them into infra red heat waves (the latter is an assumption that one should prove or disprove).
After these different kind of e-m-waves do exist ("are alive finally"), it does not seem to matter that the material below is of different structure (i.e. actually white if exposed to light or is of copper or is just air).
These kind of e-m-waves ("heat waves") have a nature that is able to "infect" (heat up) almost all other materials. And this refers both to gaseous materials such as air but also to solid bodies such as metals.
Result: A dark material is "dark" because its electron hull behaves differently when it is hit by e-m-waves (light waves), compared to an electron hull of a "bright" material.
Explanation: An explanation is easy if we assume that the material is hit by light waves with wave lengths between 397 to 656 nm:
Whitish materials (mainly) will turn the impacting light waves into visible light waves again or in other words "reflect" the light.
- Not a prove but: Feel the temperature of the copper on the backside of the curtain and compare it to the temperature of the darkish painted curtain.
- Not a prove but: One is often blended by the bright beaming of whitish objects but never by that of darkish objects.
- Not a prove but: Feel the temperature of the copper on the backside of the curtain and compare it to the temperature of the whitish curtain.
- Not a prove but: If dark objects would send out as many e-m-waves in the visible as a whitish body does, the human eye would perceive shiny objects. But this is generally not the case.-
Side remark: Not all visible e-m-light-waves turn into infrared e-m-heat-waves and some not even can (as a look at a term scheme of a spectrum shows): E.g. the alpha-3 excitation falls back from m = 3 to n = 2 whereas the infrared excitation has its base n =3 and thereby just sending out visible e-m-waves.
About the subjective darkish or whitish character of objects: One could possibly say that the human eye actually perceives surfaces as dark if a reasonable percentage of light - that hits a surface - is turned into "heat waves" and therefore "vanishes" from the human eye since the human eye is not able to perceive heat waves (at temperatures up to 100°C and way above at least).
Since less e-m-waves are turned back into light, less light waves can reach the human eye in comparison to surfaces with a "whitish electron character".
It can be assumed, since the human eye is easily deceivable, that a material only then appears as dark, if there are other surfaces around that reflect light seriously better (and thereby build an observable contrast).
On the other hand, a dark walled room containing dark objects is certainly perceived as a dark room with dark objects (but maybe also just because we know that there are brighter objects in the rest of the world).
Something clinical: To observe this thing more clinical, it can be said that an object can send out a minimum and maximum number of e-m-waves since the number of electrons are finite that can react with incoming (e-m light) waves.
So, if we look at a surface of 5*10-10 m (i.e. 25 atoms) and if we assume that only one hull electron interacts and if we further assume that the atoms don't interact with eath other we would have an y-axis from 1 to 25 units.
If we further see the time span of excitation and electron recombination ("mean time of exitation and electron recombination") as a defined known time intervall, we can estimate the maximum number of excitation-recombination intervals per time unit.
Let's just assume that each electron can experience a maximum number of 10 cycles per time unit, the x-axis then would go from 0 to 250 since we have 25 electrons (atoms) that are active.
A z-axis which would go from 0 to 100 % then could show us the amount of e-m waves that are turned back into "light waves" or changed into "heat waves".
Judging materials with this 3-d-graph, we might be able to decide more easily if we wonna regard a material as darkish or whitish.-
