A further correction . . . The LED I bought was advertised
http://www.ebay.com/itm/120896174810as:
380 to 385nm
1000mA
9 to 11V
900 to 1100mW output
actually has a peak output at 394nm. I measured it with a monochromator
from an old spectrometer. The monochromator reads correctly within 1nm
for both a 532nm green laser and for the 404.7nm mercury emission line,
so I think my reading is reasonably accurate. Half power was +/- 6nm.
When I wrote my first message I thought this was probably the same as an
identical-looking device for which there is a little more data:
http://www.leds-global.com/ultra-violet-380nm-high-power-led-modules-p-7.html375 to 385nm
1050mA
10 to 12V
400 to 500mW output
However, there is a serious mismatch in the specified output.
This LED runs at almost 10 volts with 1 amp, which matches the eBay
specification exactly, but would be at the low end of the range for the
p-7 device above. The shorter the wavelength the higher the voltage, so
this is consistent with the eBay specification being for a LED with a
longer wavelength than "380 to 385nm".
I think the eBay LED is a closer match for this one:
http://www.leds-global.com/uv-10w-390395nm-high-power-led-p-146.html390 +/- 5nm
1050mA
9 to 10V
800 to 1000mW
I don't have a chart for the wavelength sensitivity of Riston - I was
referring to:
http://www2.dupont.com/Imaging_Materials/en_US/assets/downloads/datasheets/mm500series.pdfwhich states that the "peak response" of the material is 350nm
(nanometre) to 380nm.
I was keen to get a high powered LED with as short a wavelength as possible.
While I may have paid more than I needed to for a 395nm LED, the good
news is that Riston seems to respond just fine to 394nm.
Searching eBay for UV LED 10W 395nm I find various cheaper LEDs, but
395nm is not their center wavelength - they are typically 395 to 405.
There are likely to be uncertainties regarding the actual wavelength of
LEDs vs. how eBay seller advertise them. However, if a 3 minute
exposure is OK at 30cm, which is fine for small PCBs, then I think a 3W
390 to 395nm LED would be a good, inexpensive, choice.
For instance, this supposedly 3W 390 to 395nm LED:
http://www.ledfedy.com/products/1-500w-led/3w-led/3w-uv-led-390-395nm-double-chips-with-star-pcb-1492.htmlcosts USD$4.69 - not counting postage.
A LED like this would be easy to run - just get a 12 regulated power
supply and choose a resistor which drops (12 - 3.3) volts at 0.7A = 12
ohms. The LED would need a heatsink and the resistor would dissipate
about 6 watts.
- Robin