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I recently discovered 385-400nm UV LEDs are available in epoxy encapsulated forms. Seemingly identical to the traditional through-hole red or green LED. How does this work?

I was under the impression that plastics absorb far too much UV for this to work seeing as how every UV photodiode needs not just glass window, but a special UV-glass window.

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  • \$\begingroup\$ Silicone epoxy tends to have excellent UV transmission, although it depends on the exact composition. Not a chemist but the silicon polymer probably has different electronic properties than a purely organic one. \$\endgroup\$
    – user1850479
    Commented Jul 10, 2022 at 18:28
  • \$\begingroup\$ @user1850479 Why does this not seem to be seen for photodiodes then? Is the difference just working intensity? Wouldn't it still suffer from UV degradadation? \$\endgroup\$
    – DKNguyen
    Commented Jul 10, 2022 at 18:31
  • \$\begingroup\$ I've seen near-UV photodiodes using silicone epoxy from Hamamatsu. I think you don't have lifespan issues until you're below 300nm \$\endgroup\$
    – user1850479
    Commented Jul 10, 2022 at 18:48
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    \$\begingroup\$ @user1850479 I guess my mind is thinking about plastics yellowing in the sun which is mostly UVA. unless it's actually the small amounts of UVB that are doing the yellowing and not UVA. \$\endgroup\$
    – DKNguyen
    Commented Jul 10, 2022 at 18:50
  • \$\begingroup\$ What manner of UV? 405nm is useful for a lot of UV purposes such as resin/adhesive curing of appropriate materials. Its behavior does not bear much resemblance to UVC (eg. 254nm from an Hg discharge lamp) that can damage skin, kill germs, and yellow plastics. The latter also is absorbed by ordinary glass let alone plastic (quartz is used). \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Jul 10, 2022 at 19:20

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