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<p>[QUOTE=&quot;-jeffB, post: 3275507, member: 27832&quot;]To get into &quot;you&#039;re both partly right&quot; territory:</p><p><br /></p><p>UV comes in different &quot;colors&quot; just like visible light. After you go past blue and violet, you get to UV-A, just a bit more energetic than visible light. Keep going, and you get to UV-B, more energetic and damaging, then UV-C, very dangerous indeed. Beyond that is EUV (&quot;extreme UV&quot;), then X-rays.</p><p><br /></p><p>UV-C and everything above it gets absorbed strongly by air, so we don&#039;t get much of it from the Sun at ground level.</p><p><br /></p><p>UV-B gets through the air, but window blocks it. You need something like a quartz window to let it through. Borosilicate glass (old-school Pyrex, before that brand got sold out) lets through some.</p><p><br /></p><p>UV-A gets through normal glass to varying degrees.</p><p><br /></p><p>Even blue or violet <i>visible</i> light can cause yellowing damage, so a paper left on the indoor side of a windowsill will turn yellow with time, even if UV doesn&#039;t get through.[/QUOTE]</p><p><br /></p>

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