UV wavelength differences

Kitchen Panda

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"But you already have a Rovyvon keychain light!" " Yes, but it's Prime Days and it's half off and it's got ultraviolet!" "But you already have an ultraviolet AAA light and several loose UV LEDs" " Yes, but this one is 365 nm and it's half off!"

So I bought a Rovyvon A8 because it was on sale. I was wondering if the wavelength really does matter and I'm surprised how much difference it makes. I have a AAA powered multiple 5-mm UV light bought at Home Depot, which is evidently around 395 nm - more deep purple than UV.

I looked at my capped teeth - with the longer UV, I can plainly see two caps that don't glow, whereas my remaining good teeth do show up quite brightly. The shorter UV makes all the caps glow.

I looked in my wallet. Canadian plastic currency doesn't have UV threads or dots like US paper bills do, and I don't seem to have any old paper notes left (which had dots). The Visa logo has a glowing V that barely shows up on the Home Depot light but is much brighter under the A8.

Big surprise was looking at my driver's licence. Long UV showed nothing interesting, but the short UV revealed a big logo saying "Original Manitoba" in glowing orange.

So, I am well entertained, and I can point to these very scientific observations to explain why I *needed* another flashlight.

The light also came with me on our recent 4000 km road trip. I did try it out on some hotel rooms and thankfully I have nothing to report on this. You want your white sheets and towels to glow brightly, and not the sink, tub, or toilet.
 

PhotonWrangler

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"But you already have a Rovyvon keychain light!" " Yes, but it's Prime Days and it's half off and it's got ultraviolet!" "But you already have an ultraviolet AAA light and several loose UV LEDs" " Yes, but this one is 365 nm and it's half off!"

So I bought a Rovyvon A8 because it was on sale. I was wondering if the wavelength really does matter and I'm surprised how much difference it makes. I have a AAA powered multiple 5-mm UV light bought at Home Depot, which is evidently around 395 nm - more deep purple than UV.

I looked at my capped teeth - with the longer UV, I can plainly see two caps that don't glow, whereas my remaining good teeth do show up quite brightly. The shorter UV makes all the caps glow.

I looked in my wallet. Canadian plastic currency doesn't have UV threads or dots like US paper bills do, and I don't seem to have any old paper notes left (which had dots). The Visa logo has a glowing V that barely shows up on the Home Depot light but is much brighter under the A8.

Big surprise was looking at my driver's licence. Long UV showed nothing interesting, but the short UV revealed a big logo saying "Original Manitoba" in glowing orange.

So, I am well entertained, and I can point to these very scientific observations to explain why I *needed* another flashlight.

The light also came with me on our recent 4000 km road trip. I did try it out on some hotel rooms and thankfully I have nothing to report on this. You want your white sheets and towels to glow brightly, and not the sink, tub, or toilet.
Congrats on your discovery that 365nm is "real" UV, while 395nm is barely-UV. In terms of the latter, even blue LEDs will cause some things to fluoresce, like paper or fluorescent highlighters, but nothing like a 365nm or shorter wavelength does.
 

novice

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Kitchen Panda, please be careful using UV to look at your teeth in the mirror. I'm guessing you're fairly close to the mirror, and it's reflecting that UV light back towards your eyes.
 

Kitchen Panda

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Kitchen Panda, please be careful using UV to look at your teeth in the mirror. I'm guessing you're fairly close to the mirror, and it's reflecting that UV light back towards your eyes.
That is a very good point and thank you for reminding me of the hazard here. One maker of UV drop-ins warns that 365 nm UV requires safety eyewear. They recommend testing for UV transmission to confirm that your lenses do block UV. I did the "glowing T-shirt test" and found the following:
1. My prescription, polycarbonate, safety glasses block UV, as do the red laser-enhancing glasses that came with a laser measuring tool.
2. My regular glass lenses, both every day and backup pair, in spite of anti-reflection coatings, do not block 365 nm - T-shirt glows brightly for flashlight shining through.
3. Cheap and nasty pair of what we used to call "visitor's safety glasses" at the steel mill blocks UV.
4. Two different models of ANSI Z87-approved fit-over goggles - one pair blocks UV through the lenses (but still allows it through the clear rubber goggle frame), and the other does not!
5. Full-face clear plastic face shield does not block UV.
6. I'd always believed common window glass blocks UV, so I wasn't worried about reflections in the mirror. I was wrong. UV reflected off the mirror lights up the T-shirt about as brightly as direct UV from the flashlight (I wore my safety glasses for this test!)

I will certainly wear my safety glasses for further uses of the 365 nm and I may take it out of pocket carry and put it in the workshop to discourage casual playing with it. Exception will e taking it with me to the hardware store when buying future safety goggles - make sure they block UV.

I've got to rememember that stuff bought on-line, even Amazon, does not carry the safety warnings we get with products bought at bricks-and-mortar local stores.

All my tests were short, and you can't damage your lenses if you've already had cataract surgery!
 

PhotonWrangler

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All good tests, KP. The T-Shirt test works because of a UV dye that's added to most laundry detergents to make clothes look brighter. Aim that UV light at a box or a cup of laundry detergent and the fluorescence will be really intense. You can also purchase that dye from RIT to make invisible ink.
 

KITROBASKIN

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Both of the lenses in my eyes are replaced (wonderful clarity beyond 6 feet or so) and the manufacturer says the artificial lenses block UV. However my doctor said that was not to be relied upon in the sense that the lenses are only a portion of the entire eye. This is what I remember.
 

Dave_H

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I have a Defiant 3AAA multi-5mm UV flashlight from HD, have not seen any there recently, probably same one; cost about $7. I use
18650 in mine, with a PVC tubing collar.

Package says it detects scorpions, fortunately have not had opportunity to find any.

Shorter UV (254nm) reveals fine pattern around border of Canadian postage stamps for anyone who still uses them; but longer UV including this flashlight does not.

Dave
 

Kitchen Panda

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Scorpions are very rare in this climate - lucky for me. I should try a sweep of the back lawn and see if other nocturnal critters give away their positions under UV. These are also useful for detecting pet stains on carpets.

Yes, my old UV light is the Defiant, bought years ago but they still had them on display the last time I visited HD. I tried the A8 365 nm on some Canadian stamps (we still send cards out each year at Christmas) but no fine detail showed up, just the edges glowed green. The only shorter-wavelength UV source I have around here is a 4 watt EPROM erasing lamp (erases old-style programmable memory chips with a clear quartz window on top, for those who got started in electronics after 2000!) and I'm more than a little scared to bypass the interlock with a magnet and expose the world to its power.

Many white things glow, but not porcelain plumbing fixtures. Most kinds of white paper glow, but not newsprint or brown cardboard. Many plastics glow, anything "day-glo" like paracord lights up like a lamp. But the oddest thing I found that glows under UV is the clear plastic mat under an office chair - don't know why that needed to look brighter under office light.
 

PhotonWrangler

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Scorpions are very rare in this climate - lucky for me. I should try a sweep of the back lawn and see if other nocturnal critters give away their positions under UV. These are also useful for detecting pet stains on carpets.

Yes, my old UV light is the Defiant, bought years ago but they still had them on display the last time I visited HD. I tried the A8 365 nm on some Canadian stamps (we still send cards out each year at Christmas) but no fine detail showed up, just the edges glowed green. The only shorter-wavelength UV source I have around here is a 4 watt EPROM erasing lamp (erases old-style programmable memory chips with a clear quartz window on top, for those who got started in electronics after 2000!) and I'm more than a little scared to bypass the interlock with a magnet and expose the world to its power.

Many white things glow, but not porcelain plumbing fixtures. Most kinds of white paper glow, but not newsprint or brown cardboard. Many plastics glow, anything "day-glo" like paracord lights up like a lamp. But the oddest thing I found that glows under UV is the clear plastic mat under an office chair - don't know why that needed to look brighter under office light.
I don't think the plastic mat fluorescence is deliberate. It's more likely that one of it's ingredients is some petroleum derivative that has natural fluorescence.

I have a shortwave UV lamp for erasing EPROMS also. Haven't worked with those chips in ages, but when I was doing some iterative work that required several re-loads of EPROMs for a device, it came in really handy. Unfortunately those shortwave mercury lamps put out a lot of visible light so any fluorescence they might deliver will be somewhat masked by it's visible output. I purchased a shortwave UV filter awhile back and I'm going to fit it to one of those UVC lamps.
 

Kitchen Panda

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I checked our passports under the UV lamp and appreciated the hidden artwork...what looks like a line engraving of the Parliament Buildings turns out to have a great fireworks show over it when the UV hits!
 
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