eli5: why does glass absorb infrared and ultraviolet light, but not visible light?
In: Physics
“Glass” is a big concept, and different types of glass absorb or reflect different wavelengths of light differently.
Ultraviolet for instance is neither reflected nor absorbed by most types of glass used in the home or vehicles. We have the technology to make UV-blocking glass, it just has a slight cost premium. You, the consumer, can buy it! I highly recommend it, because the damage that UV light does to the interior of your house and car is real, but especially the damage it does to your physical body. You don’t want to get skin cancer or premature aging.
Infrared has less horrible effects than skin cancer but its effects are more relevant to your day-to-day in that it affects your home heating/cooling bill, or in the case of homes in the US, whether your home is livable at all when the grid goes down. Wealthy homebuyers and architects love using glass, but the panes they typically use are cheap (so they can use a lot of them) and without a powerful HVAC system will turn your house into an oven during the day and an icebox at night. Different panes like triple-pane glass, different formulations of glass, different impurities, or just using shutters can all completely change this. Green engineers redesigning the suburban home consider glass one of their top priorities, as much as saltwater batteries and solar panels.
Visible light can in fact be blocked by glass, and even blocked one-way, as in one-way mirrors. “Colored” glass by definition blocks all visible light except one color, and that’s medieval technology. I’ve even seen privacy glass that can be electronically turned off (completely transparent) or on (opaque), and solar glass that not only absorbs but photosynthesizes impinging light.
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