Real UV flashlight

[Sigurthr]

It's not eye fluorescence. It is true spill; I put a >400 pass filter in front if the LED and checked it with my spectroscope; continuum fluorescence from 400nm-780nm (range of my scope). It was pretty low level, maybe 250mililumens at most.

I think some 380nm-ish spill (judging by perceived color) may be washing out the 365nm from my vision when I look at the beam/spot. I found a site weeks ago that had a wood's glass round for sale on the cheap, but I didn't save it and I have to find it all over again now.

 

[zyxwv99]

Thanks for that answer. I have a 1W Tank007 365nm and was wondering about the white spillover. Now I'm going to be looking more seriously at filters.

 

[Atomicrox]

Just looked at my 365nm flashlight with a diffraction grating. I see a *lot* of red/yellow/green light, a bit of blue/violet and then a fat line below the violet. It looks like a cross between cyan and violet, but kinda pale. I'm guessing that's the UV.

 

[Sigurthr]

Yep that lower fat line is probably the main emission band (360-385nm), unfortunately the higher wavelength components tend to wash out the 365nm peak a bit in vision giving it a more white color.

 

[Atomicrox]

Today I compared a UV "blacklight" tube, the flashlight and a 405nm laser dot under the grating.

As for the tube, I see two lines very clearly, one violet and one bluish. There's also a very faint greenish line.
After aligning the laser, the tube and the flahslight on the same level I'm no longer sure the fat line of the flahslight is the UV - it falls around the same area as the laser and the tube violet line and the colors aren't very different. It's probably just 390-410nm washing out the rest...

 

[Sigurthr]

The lines from the black light tube can be used as reference points as they are mercury spectral lines:

365nm 404nm 435nm 546nm

Typically unless high grade optics and filters are used even super weak 404nm washes out any 365nm. Oh, and most gratings are plastic which will not pass <400nm.

 

[Atomicrox]

That's it, I'm certainly seeing 404nm 435nm 546nm. And I have a plastic grating.
Damn :/

 

[Sigurthr]

Yeah, I feel your pain. I can't afford a glass grating either.

To make it worse, my spectroscope has linear wavelength markings, but the spectra provided by the plastic grating is nonlinear. I can calibrate the markings to say the 435nm line with good precision, but then anything below 415nm or so is out of calibration; the 404nm line appears at 411nm. If I use the 546nm line as a calibration reference then 430-620nm appear to be within calibration, but 632nm appears at 640nm. Shorter wavelengths are thusly more affected by the nonlinearity of the diffraction. This of course would be corrected for in a proper spectroscope by having the wavelength scale markings nonlinear to compensate. In addition; it is a "direct sight" scope where the eyepiece has the grating and you're seeing the first order spectra that is sent back towards the slit instead of the grating being after the slit and the eye piece looking at the target. The result is that strong sources glare on the grating as the eye piece is always in direct line of sight of the light source through the slit.

TLDR; I'd kill a (bad) man for a proper spectroscope.

 

[Atomicrox]

I think I'll set up a "wall spectroscope" to measure my lasers. All I need is a fixed distance and a proper scale on a few A4 sheets glued together... Shouldn't be hard to get 1-2nm of precision.

But then again that won't work for flashlights.

 

[Sigurthr]

It's too bad spectrometers cost about the same as a used car...

 

[BShanahan14rulz]

I think I'll set up a "wall spectroscope" to measure my lasers. All I need is a fixed distance and a proper scale on a few A4 sheets glued together... Shouldn't be hard to get 1-2nm of precision.

But then again that won't work for flashlights.

^ pinhole may help. Not a lot.

 

[Sigurthr]

HeNes make good reference points for wall scopes as you know it is ~633nm/543nm regardless of thermal drift (unlike diodes that shift +-10nm).

Mercury lines make great reference points too but it's hard to get it setup for a wall scope. Sodium D line(s) is another great reference at 589nm.

 

[BShanahan14rulz]

Green laser too

 

[Atomicrox]

I'm planning on using 532nm as reference. I don't have any gas lasers and buying one internationally will be complicated.

 

[bloompyle]

Torch came in today, very cool! Never thought I'd find so much subtle enjoyment in a UV light. Was not prepared for how dim 1W of 375nm would be, it's barely anything, but it lights up my neon shoelaces from across the room. Very cool!

 

[Sigurthr]

Heh, you're mostly seeing the NUV splash anyway.