UV question.

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VidPro

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I dont really ever need UV, i was just playing with it for fun.
i installed Blacklight UV leds and they were cool dark purple and pretty visable, but useless for florescing organic materials (410).
SO
i finnaly found a reasonable price on more "shortwave" UV leds, of 365 wavelenght. but the visable output of them is sooo dark and useless looking.

i am wondering, did i get cheep cheesy low output UV leds (they were cheap) or has this now fallen so far out of my range of vision that it just looks that way.

ALSO
the Vf of the led is around 4V to reach spec currents, wheras the 410leds was around 3.6v or thereabouts.
is this Par for a UV led of shortwave to have a higher voltage gates?

what do they concider the wavelength that the human can no longer see in the UV side of the spectrum?
 
Last edited:
i finnaly found a reasonable price on more "shortwave" UV leds, of 365 wavelenght. but the visable output of them is sooo dark and useless looking.

i am wondering, did i get cheep cheesy low output UV leds (they were cheap) or has this now fallen so far out of my range of vision that it just looks that way.

Compare the 410 and the 360's by how bright the fluorescence is from a fluorescent colored object, e.g. bright orange road cones. If the brightness is similar, you've got good 360nm's. Based on the 365nm wavelength from CFL blacklights I have, 365nm is just barely perceivable, and only as an ultimately deep purple.

the Vf of the led is around 4V to reach spec currents, wheras the 410leds was around 3.6v or thereabouts.
is this Par for a UV led of shortwave to have a higher voltage gates?

Yup; the shorter the wavelength, the more energy there is per photon, so the average voltage drop gets bigger as the wavelength gets shorter, for a given current.
 
Also, remember that a UV LED does not have a negligibly-wide spectral spike, but a rather broad range of output emissions, possibly 10-20 nm wide, not counting the false emissions from those recent ANNOYING fluorescent-package HK LEDs!! :( :shakehead :scowl: :( :shakehead :scowl:

For a 410nm LED, it could be that virtually all of the output is visible, but that most likely wouldn't be true for a 365. In either case, the longer-wavelength side would be the most visible, and would tend to shift the dominant wavelength (that perceived as the color of the LED) towards the blue. For the shorter-wavelength UV LED, the eye may not even see the peak wavelength emission at all, just the longer-wavelength tail, making it appear dimmer still due to the low percentage of power in the tail.

You definitely can't go by how bright the LED appears. I'm also not sure about using fluorescent materials to determine relative LED output. These materials have their own response peaks, and probably will not respond anywhere close to the same way at those two wavelengths. (see last paragraph below for an example of this.)

I don't know how constant the short-wavelength perception limit is for various people, and it would depend on intensity as well. There may be some point past which the eye could detect a short wavelength, but only at power levels high enough to produce rapid eye damage.

On a side note, I have found a way to fairly reliably order UV LEDs by wavelength: shine two on a CRT TV or monitor screen. The shorter-wavelength one will make a greener spot on the screen, while the longer will look more violet. This is due to the fact that shorter wavelengths, though still appearing a purple color, also look dimmer, yet fluoresce the screen more brightly. So the spot color shifts rapidly from violet to green as you go from 420 to 380 nm. I have not tested the effect at shorter wavelengths than this.
 
VidPro said:
what do they concider the wavelength that the human can no longer see in the UV side of the spectrum?
Click to expand...

This is something that I've wondered about also. The think is when you look at a 365nm blacklight source, your corneas fluoresce! This messes up one's ability to determine whether you're perceiving the UV wavelength or the longer-wavelength fluorescence of your eyes themselves.

I have a shortwave UV lamp with a filter; Craig reviewed it on his website a good while ago. When looking at that lamp (which I DON'T recommend), I can perceive a very dim, very deep purple. It's probably the richest, "purplest" version of purple that I've ever seen anywhere. This seems to suggest that that there's still the tiniest amount of sensitivity to UV at the far end of the spectrum, around 235nm.
 
I have a Streamlight UV Stylus, just bought it as a gimmick, but what are some uses? Other than checking ID ;-)

I also have an Inova X5 in blue, got any uses? No, I don't hunt...
 
thanks everybody.
i finished it, and really it was more "fun" with the dark purple 410 blacklight ones in it.
Although,
now it does certannly light up the strip on the money, without lighting the money itself , and i can finnaly see there is a BEAR on my California drivers licence.
BUT
i think i coulda seen all that with ONE in a press keylight thing.
this has 12 in it being driven to spec, and i still cant see much of anything.
THEN
i tried it on "organics" again, still cant see the dog urine, mabey my dogs dont drink enough antifreeze :) (umm that kills dogs ok)
SO
i figured Organics? heck i am organic , and it doesnt floresce on me neither :)

oh well, it is now shorter wave, and actually does do the mony and "security" things, other than that its rather dull.
 
UV charges glow material too, there was a pic of a scorpion being lit up by UV, lemme see if I can find it...


scorpionlargeuvonkt9.jpg
 
PhotonWrangler said:
When looking at that lamp (which I DON'T recommend), I can perceive a very dim, very deep purple. It's probably the richest, "purplest" version of purple that I've ever seen anywhere. This seems to suggest that that there's still the tiniest amount of sensitivity to UV at the far end of the spectrum, around 235nm.
Click to expand...

That's a very curious observation. Did you try to filter out any other peaks, such as the weak 405nm mercury emission peak? That could be accounting for the deep purple visible. Dim violet does tend to look deeper than bright violet of the same wavelength. I think there are other intervening mercury emission peaks as well, though I don't know their locations or intensities right off hand. If you're sure that all other peaks have been accounted for, it would be very interesting if we could see (though with great ocular risk!) 235nm. It would seem that the eye would have zero ability to focus this light in the usual way, so it would have to be by some other (eye-destroying!) mechanism. :thinking:
 
lyyyghtmaster said:
That's a very curious observation. Did you try to filter out any other peaks, such as the weak 405nm mercury emission peak? That could be accounting for the deep purple visible. Dim violet does tend to look deeper than bright violet of the same wavelength. I think there are other intervening mercury emission peaks as well, though I don't know their locations or intensities right off hand. If you're sure that all other peaks have been accounted for, it would be very interesting if we could see (though with great ocular risk!) 235nm. It would seem that the eye would have zero ability to focus this light in the usual way, so it would have to be by some other (eye-destroying!) mechanism. :thinking:
Click to expand...

I'm certainly open to the idea that I might have been seeing the 405nm peak, although to my subjective eyes it was a deeper purple than what I've seen from the shortest wavenength UV LEDs, or even from longwave BLB-style fluorescent blacklights. I'd love to be able to separate each wavelength out and gauge my ability to see it (briefly, of course!) but I have not done so thus far.
 
FWIW, I had Lasik with an excimer laser (193nm UV) and I didn't see any light at all. And I really had my eyes peeled for it. :laughing:
 
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