[alt-photo] Re: LED exposure lights

[etienne garbaux]

>Good question and I think there is some discussion on this in the 
>archives, but mostly speculation.

There was a short thread in early December 2009 that started with a 
question about using a UV LED as the source for a UV 
densitometer.  Andy Schmitt noted that some DIY printed-circuit 
constructors use homemade UV LED light boxes to expose the etch 
resist, and that he had bought supplies to make a light box for photo 
use.  I do not believe he has reported on his results.

>I have done some web searches and there are LED lights for UV that 
>are very narrow in spectrum range and tuned to very specific UV 
>values.  They are still expensive, but that may change in the 
>future.  I'm not sure that they put out enough light though.

Well, it depends on how many you use.  If you pack them together as 
tightly as possible (which would require from 5,000 to 10,000 LEDs to 
make a 16x20" light box, depending on their size) and place the array 
within an inch or two of the media, I suspect there would be plenty 
of light.  (This is what the PC constructors do, but their exposure 
boxes are generally no larger than 5x7".)  If you want to expose 
16x20 prints with an array of 100, probably not.  There are plenty of 
good candidate LEDs with peak outputs around 400 nM for less than a 
dollar each (here's one for $0.66: 
https://www.alliedelec.com/Images/Products/Datasheets/BM/VCC/398-0973.PDF. 
Some assembly required.     ;-)

Best regards,

etienne