Why do things get sun bleached through a window but you don’t get a sunburn when sitting near a window?

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Why do things get sun bleached through a window but you don’t get a sunburn when sitting near a window?

In: Chemistry

Ultraviolet rays are broken down into two types: UVB and UVA. Normal windows block most UVB rays which are the ones responsible for sunburn. However, they still let in UVA rays, which can still cause bleaching.

The amount of UV rays that makes its way through a window is not quite enough to cause a sunburn, but you can still get tanned from it. IE: The ‘trucker tan’.

Things sitting next to windows will also be affected by the UV rays, just not as much as if they were sitting outside directly in the sun.

There are a couple of reasons. The first is that sunlight is made up of lots of lots of different wavelengths of light different wavelengths interact with objects in different ways. Some of the wavelengths will get absorbed or reflected by certain objects and materials while other wavelengths may pass right through them. With windows, the wavelengths most commonly responsible for sunburns largely get blocked by windows while the wavelengths that bleach the color out of objects is able to pass through.

The second reason is time. You may sit next to a window for only an hour or two while an inanimate object might stay there continuously for months or years. Because it sits there for so long, the energy of the sunlight that passes through the window can cause a far greater effect than it can in the brief period you sit there.