UV filters

jspeybro

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seems that they are meant to transform lightsources that contain UV, amongst other coloors, into a UV-only lightsource.
I suppose it would be OK, but doubt the transmission will be much more than 50% for 365nm. since there is no datasheet, it's difficult to tell what the blocking power is for longer wavelengths (visible/NIR). From what I see with filters at my work, I doubt it will block near infrared.
I could do a transmission measurement at work, but I don't have the filter.

could you give a bit more info on what you want to do, perhaps I can recommand a filter. In some cases it is cheaper to just use 365nm emittors
 
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lucca brassi

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Kocevje , Slovenia, Europe
Correct. I have friend from Ljubljana which made beautiful photos of sealife and also some endemic creature like ''protheus'' which lives only in our ''karst caves'' . I have put link from pictures of '' human fish ''as we called here and article published in UwP in pinned Divelight Library and also some project from Scubaboard.

Friend made photos by blocking HID Salvo 21W with filter like these , he uses also yellow gogles over mask.... pictures are just fabulous . System for taking pictures is also described in article.

I have thought due to power leds spectrum that might work also with them . Positive is also that to avoid too expensive UV leds and you have to take only one light under water with filtre.
I think also that common light output with single or multiple power leds is much bigger than with special 3W UV leds .
 

jspeybro

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ok, I see.

Some german guy once posted this video in the welcome divers thread, but apparently that got lost:
http://www.youtube.com/watch?v=HnL1xTKQjNw
He uses blue leds instead of UV leds. While this wavelenght (445-450nm, something like that) is about 100nm longer, this is still able to excite the fluorescent substances of sealife as you can see in the video. I even read somewhere that for corals, the ideal wavelength is rather blue than UV.
Cree has these LEDS, the royal blue ones are the one you want. (about 460nm)
I tried this LED from dealextreme once in a ultrafire W200 and while it worked, there wasn't much to see that showed fluorescence in our waters.

The yellow filter that your friend used, was to block the excitation light so that you or the camera only sees the fluorescent light and not the excitation light. This is important because the excitation light is much more intense than the fluorescent light so the get the best result (certainly with pictures), you'll need a filter that blocks the excitation light. Yellow filters are probably the easiest way to do that, because it allows some green, yellow and red to pass and block blue.

These leds from dealextreme are cheap and give a quite some light, certainly if you make a head with multiple leds.
Yellow filters for camera's can be found for a few dollars on ebay.

This ofcourse doesn't answer your question regarding the dealextreme filters, but may be an alternative to what you want to achieve.

Johan
 

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