Saw an amazing UV light the other day

[PhotonWrangler]

I was walking around a hotel gift shop when I noticed a plain rectangular UV fixture. Actually I first noticed that a lot of items in the area were fluorescing and I had to really hunt to find the source of the UV light. It turned out to be this rectangular box with a flat Woods Glass filter in front of it and no discernible visible light emanating from it! The only thing that was glowing on the lamp itself was a few specks of lint on the glass. Wow. I have never seen a UV filter that good before. The cutoff curve must look like a brick wall.

The nameplate on the back of the lamp said Spectrachrome Model 93LIGHTB, Lamp 4-36w-PL. It was apparently built for demonstrating a brand of of t-shirts and jewelry featuring photochromic inks that change color in sunlight.

I held my cell camera up to the lamp and 'lo and behold, I could then see the bulbs. They appear to be a set of 4 BL-style "bug zapper" style bulbs. I was also surprised to find that my cell camera had some sensitivity beyond 370nm. 😎

**Update**
Finally got around to uploading some pictures of this lightbox. I wish these were available to the public but they appear to be a custom build. Because the cellphone camera has sensitivity into the UV range, the bulbs are clearly visible, but to the naked eye this lightbox emits no visible light whatsoever.

 

[PhotonWrangler]

:bump:

Anyone else seen one of these in the wild? I'd love to have one, or at least a sheet of whatever type of Woods Glass they're using.

 

[shao.fu.tzer]

I haven't seen them but they seem to be some kind of CFL (obviously)... Interesting... I wonder what wavelength they operate at...

 

[PhotonWrangler]

I haven't seen them but they seem to be some kind of CFL (obviously)... Interesting... I wonder what wavelength they operate at...

They're running at 365nm, the classic fluorescent "blacklight" wavelength. The bulbs themselves appear to be the unfiltered BL type of blacklight bulb, commonly found in bug zappers. I could see a little bit of unfiltered blue light leaking out of ventilation holes in the back. What's special about it is the sharp cutoff of the glass filter in front. The only way I could tell it was turned on was from a few specks of fluorescing lint sitting on the filter. A very impressive job of filtering out all visible light!

 

[LEDAdd1ct]

—just looked at your photos. Very, very cool. I wish I had the information you are seeking so I could help.

 

[FRITZHID]

Hi PW, long time. I got lost in the CPF server crash 🙁 but, if you remember, you and i discussed trying to find woods glass or any kind of UV pass filter that i could use on my stanley HID. have you had any luck on your end? (i unfortunately have not, almost ready to resort to breaking a florescent BL bulb @ this point.)

 

[PhotonWrangler]

Hi PW, long time. I got lost in the CPF server crash 🙁 but, if you remember, you and i discussed trying to find woods glass or any kind of UV pass filter that i could use on my stanley HID. have you had any luck on your end? (i unfortunately have not, almost ready to resort to breaking a florescent BL bulb @ this point.)

Hi Fritz, good to see you again. I found a 5-1/4" round UV pass filter from Rosco that's carried by BH Photo. I'm considering ordering one of these myself. However after trying out that fluted UV filter that I purchased awhile back, I think I also need to change out the stock bulb in my Stanley HID as I think it doesn't produce that much energy around the 365nm band. Or perhaps the plastic lens in front of the bulb is uv-absorbing. Note to self: remove the lens and try the filter again.

I noticed the same phenomenon when I purchased a Philips mercury HID blacklight bulb awhile back. It's basically an ordinary mercury HID lamp with a woods glass envelope, and it doesn't produce nearly as much blacklight as I expected for it's 175 watts. I could get almost the same amount of usable UV from a 15 watt CFL blacklight bulb, as the CFL is made with the blacklight phosphor coating on the inside while the Philips 175w lamp (apparently) isn't.

**Update**

I've just removed the lens from the front of my Stanley HID and I've tested it by shining both a 365nm LED and a 395nm LED through it while viewing a fluorescent target. I've confirmed that the lens is not contributing significant attenuation of longwave UV wavelengths, so it looks like the lamp itself might be deficient in longwave UV energy. This means I will be searching for different H3 bulbs for this light.

**Another update**

I've found a pair of 4300k H3 bulbs pretty cheap so I've ordered them. I don't think they'll make a lot of difference in terms of UV content since these bulbs seem to have a UV-blocking coating on them to protect the plastic headlight lenses from deterioration, however I will retry my UV filter with them anyway and report my results here.

 

[FRITZHID]

hey PW,
i had another thought.... notice when you run an HID bulb for a while, shut it off and look at it while the quartz envelope is still red/hot, the outer glass shield glows blueish. perhaps that is blocking a significant amount of the UV?
IDK how easy/safe it would be to bust that off w/out breaking the chamber but may be worth a try as well. if i could find a filter i would certainly try! ;D

 

[PhotonWrangler]

hey PW,
i had another thought.... notice when you run an HID bulb for a while, shut it off and look at it while the quartz envelope is still red/hot, the outer glass shield glows blueish. perhaps that is blocking a significant amount of the UV?
IDK how easy/safe it would be to bust that off w/out breaking the chamber but may be worth a try as well. if i could find a filter i would certainly try! ;D

Yes, I've noticed that also Fritz, however I've also noticed that bluish glow after turning off a UV germicidal lamp, and those are designed to pass UV. :thinking:

 

[FRITZHID]

Yes, I've noticed that also Fritz, however I've also noticed that bluish glow after turning off a UV germicidal lamp, and those are designed to pass UV. :thinking:

yeah, there is that, but i'm wondering if what ever they dope those types of glass with, have an inherent reaction to the IR light/heat given off? i'm still thinking that if we remove that tube, we MAY get in increase in the UV output, since those are designed to protect the plastics in headlamps from UV degradation. our other choice would be to find a compatible Xenon Short Arc that would fire off that 35w ballast. since stanley uses such a unique type, they May fire, who knows?

 

[PhotonWrangler]

Update -

My 4300k H3 bulbs arrived today, so I tore down one of my two Stanleys and promptly replaced the bulb. It's a bit of a PITA and took a little longer than it should have, but it's done. And the new lamp has a much warmer color temperature.

But now my other unmodified HID is dead. I get a solid green charge light but the battery won't charge. So now I can't compare the relative UV content of the two bulbs.
:shakehead

 

[FRITZHID]

Update -

My 4300k H3 bulbs arrived today, so I tore down one of my two Stanleys and promptly replaced the bulb. It's a bit of a PITA and took a little longer than it should have, but it's done. And the new lamp has a much warmer color temperature.

But now my other unmodified HID is dead. I get a solid green charge light but the battery won't charge. So now I can't compare the relative UV content of the two bulbs.
:shakehead

damn! well that sux. is it the batt or ballast? (*pray'n* plz be batt, plz be batt) well keep us updated. its a shame if it is the batt, i have 7 spare 12v 7.2Ah SLA's sitting here.

 

[PhotonWrangler]

damn! well that sux. is it the batt or ballast? (*pray'n* plz be batt, plz be batt) well keep us updated. its a shame if it is the batt, i have 7 spare 12v 7.2Ah SLA's sitting here.

I'm not sure yet. Fortunately if it is the battery, there's a battery shop not too far from me that specializes in battery rebuilds and upgrades. They might be able to get this upgraded to at least an NiMh chemistry. We'll see.

 

[bshanahan14rulz]

yeah, there is that, but i'm wondering if what ever they dope those types of glass with, have an inherent reaction to the IR light/heat given off? i'm still thinking that if we remove that tube, we MAY get in increase in the UV output, since those are designed to protect the plastics in headlamps from UV degradation. our other choice would be to find a compatible Xenon Short Arc that would fire off that 35w ballast. since stanley uses such a unique type, they May fire, who knows?

This sounds like a good starting point. That outer envelope glows blue after the lamp has been shut off, makes me think it's been absorbing energy and reradiating it as heat or visible.