Why is it that we can feel the heat of the sun through glass?

Question

However, if a piece of glass were separating me and a plug-in heater, I could not feel the heat from the heater?

Answer 1

Infra red radiations coming from the sun

Answer 2

Glass reflects infrared radiation, but is transparent to visible light. The sun energy ouput is mostly in the visible area of the spectrum, so that energy will go though the glass and will be absorbed by any opaque object beyond as a function of its darkness (dark objects absorb light, that is why they are dark). Hot objects tend to give up heat back in the form of infrared radiation, unless they are hot enough (red hot, white hot) to produce visible light (that is how the lightbulb works, and also why it is inefficient as it produces a lot of heat for the light it emits).

Your heater works like a lightbulb, but at a lesser temperature, that is why the element glows red and not white. This implies it puts out most of its energy in the infrared (heat) area of the spectrum. Which is precisely where glass does not transmit well (and also explains why a car parked in the sun will get so hot inside: light comes throug the windows and windshield, heat cannot get out through that glass; and you have what is called a green house effect).

Answer 3

To begin with, your claim that you "could not feel the heat" from a heater behind glass is incorrect, although it might take a fair amount of time to feel the heat.

The answer is that glass is neither dense nor reflective enough to absorb the full energy of the sun's rays. Sunlight is (as you probably know) transmitted in the form of photons which are travelling at or near the speed of light for most of their journey (and by necessity are transmitted at a significantly high level of energy).

The same is true of your heater, although in that case, the energy might take longer to create the sensation of warmth because it is being transmitted differently - in that case an electrical current heats coils which transmit heat to the surrounding air and by extension, the glass, which would, in time, absorb heat and transmit it into the adjoining space.

Answer 4

Heaters often work via convection/advection. If you block the flow of air the the air can not transport the heat to you. It can also heat by radiation. The wavelenth of solar heat is shorter and may pass through a pane of glass that would absorb or reflect the longer wave radiation of the heater.

Materials can be opaque at certain wavelengths and transparent at others. An example of this is how a blouse made of certain materials (usually synthetics) may cover your modesty to the human eye, but a camcorder using Infrared night mode can see right through it.

Answer 5

Glass transmits quite a lot of infrared radiation which is what gives you the warm feeling. I guess it does not transmit IR that well as scientists use salt plates when they want something to pass IR radiation. I suppose your "plug-in" is not powerful enough or is it a convector? in which case it just warms the air and does not emit much radiation.

Answer 6

this is becuase, ultimately, the sun radiates ultraviolet light, which will excite (heat up) the molecules of the objects it falls upon; It is the light that sort of carries the heat, and it passes through glass. (the glass absorbs some of the heat though, and glass that is thick enough can absorb a significant amount of heat, which is how greenhouses work).

Answer 7

the rays of the sun are far more powerful than a space heater.