Hi all,
does anybody know much about UV LEDs and the differences between them?
I have a batch of UV leds from ebay, and a batch of UV leds from another
chinese wholesaler.
The ebay ones were sold as 395-400 nm, viewing angle 20-25 degrees,
30mA, 3.2-3.8v
The other ones were sold as 395-400 nm, 3.2-3.4v, 20mA, viewing angle 30
degrees.
The ebay ones stated 2000 mcd, but I wouldn't believe that (nor is it
useful for UV to state an mcd which is about visible spectrum), the
other ones claim 150-200 mcd which seems a reasonable claim for the
visible output.
I had some time ago made an exposure box out of the ebay ones, and
killed some over time (was pushing a bit much current through them I
think, being they are tightly packed the heat was building up pretty
good), so I replaced 1 complete column and a couple of other failing
ones with some of the chinese wholesaler batch, in the slideshow here
I've tried to capture the difference...
http://www.flickr.com/photos/93638530@N08/sets/72157632863117628/show/The two batches in the off state are both water clear, 5mm, identical
appearance, but as I hope you can see they differ REMARKABLY in their
visible light in the on state - naturally visible light isn't too
important here anyway, but such a big difference surprised me enough to
think I'd been sold fakes.
The ebay ones look "like you would expect UV leds to look" they emit a
little violet light, the other ones emit a quite strong light blue,
cyan, sort of colour.
At an angle, the ebay ones in the on state are largely visibly
transparent, the other ones are opaque with visible colour.
I did a quick test exposure (with dry film) and interestingly the
wholesaler ones exposed MORE strongly, that is, the exposed areas were
noticeably darker, so definitely they are putting out a decent amount of
UV in at least a wavelength suitable to expose dry film, but I'm curious
as to why there would be such a large difference visibly.
So, anybody able to share any insights into this phenomenon?
---
James Sleeman
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