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I have been reading in this and found a statement saying : " Glass will not transmit heat radiation.". So now I am confused. If glass won't transmit heat radiation, then why do we feel hot when we sit in front of a glass window in a sunny day ? Also, why do we find the car seats facing the windshield so hot in a sunny day ?

One other thing, let's say a nuclear detonation happened somewhere nearby and I was standing behind a glass window, will this window protect me from thermal or heat radiation effects of the bomb ?

Abanob Ebrahim
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4 Answers4

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This very nearly a duplicate of Does infrared rays pass through polarized glass? if you ignore the bit about polarisation.

There is a useful collection of articles about the optical properties of glass on the Schott web site, and in particular there is one titled TIE 35: Transmittance of Optical Glass. The article is freely downloadable, though you need to give Schott you e-mail address, and if you download the article you'll find detailed spectra of glass in the infra-red region. The relevant graph is this one:

Transmittance

showing that the transmittance in the near infra-red falls to zero around 2500nm (the limit of human eyesight at the red end of the spectrum is around 700-800nm). The Sun emits strongly between 750 and 2500nm, which is why the Sun will warm you through a pane of glass.

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John Rennie
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The window will not protect you. Due to the Maxwellian distribution of thermal energies of the weapon plasma, a significant fluence of visible light can be transported through the atmosphere, the window, and your eye prior to cataract generation. So while the window can block the infrared, it won't block the visible. Nuclear weapons generate thermal radiation from the infrared into the hard x-ray spectrum.

user22620
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Your statement is correct. However, you might still be affected as there are other forms of Thermal transfer such as Conduction.

siva
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That sounds wrong. Also, later it somehow contradicts itself by saying

  1. A greenhouse keeps warm inside because of the properties of the glass. The short wavelength radiation from the Sun can get in but because the plants and soil are cooler they emit longer wavelength radiation which cannot escape through the glass.

Heat radiation is mostly electromagnetic radiation in the near to mid infrared portion of the spectrum. Depending on the glass, they let more or less of this go through it. It certainly will stop heat by convection to propagate, but still the glass will get eventually hot and then heat to go through it and heat the air on the other side. As you mention, we feel the heat from the sun inside cars,

As a side note, it's interesting that teams are trying to make smart windows that change their infrared reflectivity based on temperature such as to reflect more when it's hot.

I'm not a nuclear safety guy, but I would say that a glass window certainly will not protect you from thermal radiation or any radiation if a nuclear bomb explodes in your neighborhood.

Ignacio Vergara Kausel
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