Why is ultraviolet light not transmitted by glass

Active Oldest Votes. Improve this answer. And people think that the germicidal lamps are made of glass, even though they are made of quartz I'm trying to understand cf. The bandgap for quartz is bigger than for glass. So the UV light can't get absorbed, because there is nothing to absorb it. Show 1 more comment. The values depend a bit. Quartz glass has a larger gap than lime glass and borosilicate glass. It may only have a lower density of states at some energy range, but definitely not as low as it would be in a crystal.

Think in terms of tight-binding theory. After all, re-crystallization can result in any of these forms, in which electronic structure differs considerably due to differing symmetry. But of course the crystalline form is birefringent and optically active while the amorphous solid is isotropic. Also molten salt will have the same band gap as crystalline rocksalt. Long-range order does not matter that much.

Britney's pictures didn't help, but your keywords "photon passing through material" lead me to the track I was looking for. Show 4 more comments. Sign up or log in Sign up using Google. Sign up using Facebook. The electrons in glass are arranged on different levels and can change from level to level, but such a change requires energy. Photons carry energy from visible light as they encounter glass, but this energy is not enough to move the electrons in the glass to a higher level.

As a result, the photons do not interact with the electrons in the glass at all and simply pass through. This process is known as transmission, and it gives glass its transparent appearance. You did not specifically ask about automobile glass, but that also is an issue for exposure to UV-A. The Skin Cancer Foundation states that windshield glass is specifically treated to remove the UV-A; however, the side windows and rear window will allow the UV-A to penetrate the interior.

Therefore, care should be taken in vehicles, as well. Window tints can be applied to automobiles, but be aware that states have regulations on tinting. In summary, typical window glass such as that found in homes will block most of the UV light from entering your house with the exception of UV-A light. Exposures to UV-A light can affect your skin if you have extended exposures to the light.

The addition of solar window films to the interior of the windows can reduce most, if not all, of the UV-A from entering your house. In brief, some types of UV light can pass through window glass.

Paul A. Charp, PhD.