The gaps between rows correspond to specific quantities of energy, or quanta. The way these quanta are arranged in glass is such that moving to a free row requires much more energy than is available in visible light. Consequently, visible light does not have enough energy to allow the electrons to upgrade their seats and has no choice but to pass straight through the atoms. This is why glass is transparent. Higher-energy light, on the other hand, such as UV light, can upgrade the electrons in glass to the better seats, and so glass is opaque to UV light. This is why you can’t get a suntan
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