Testing multiple UV lightsources and their color rendering

[Fandyus]

Hello.

Today I have decided to test a few different lightsources that emit UV intense enough to take pictures with:

-BeamZ 25w UV Blacklight compact fluorescent bulb

-Repti Planet UVB 15.0 compact fluorescent bulb

-Domáce Slnko UVIR (a potentially dangerous home tanning machine from probably the 70s or 80s, more info here)

-full spectrum Speedlite 199A (very similar to sunlight)

-Alonefire H42 12 core 365nm LED torch (a UV blacklight with a decently wide peak)

 

I set up the following scene:

Here you can see:

-a filter case (background)

-a PTFE sheet

-a uranium liquor glass

-a ZWB1 2mm thick filter

-a carrot and an apple set on a white ceramic plate

 

And here are the results, left side is color balanced on the PTFE, right side had color balance turned off in Darktable.

 

Rest assured, I followed basic safety, tried to get exposed to the lights as little as possible and wore yellowed protective goggles. The UVIR discharge lamp briefly smelled a little like bleach when turned on but stopped rather soon. I have no idea if that's the smell of ozone and if it emits UVC, but I ventilated the room well afterwards. The UVB light is safe to get exposed to for short periods of time according to reptile forums which I consulted, even then, I only exposed myself to it briefly. I must say the UVIR discharge lamp also looks really scary when turned on, it emits really intense ghostly blue shine, it also takes a while to reach peak output but when it does, it might be the strongest UV source I've ever handled. If it was collimated it might produce shorter exposure times than those available while outside.

 

Overall, when I briefly tried the UVB light yesterday, I was rather disappointed as it didn't look green at all, which I expected, and relative to sunlight it produced a yellow shine that was almost identical to how I remembered the fluorescent blacklight's shine, however, it turns out it produces much more colorful results, perhaps even a bit better than the sun, since the ratio of 365nm to UVB is skewed more towards UVB. The Speedlite 199A which produces a spectrum very similar to sunlight shows way less color.

I also plan to sand down the reflector on my table lamp that I screw the bulbs into, as the white paint it is using right now is not very UV reflective besides the 390-400nm region, at least that's my guess due to the fact that it appears very purple in sunlight. Currently I just taped some aluminium foil to it, but that's far from ideal.

 

Next I would like to try the Exo Terra UVB 200 25w, which should be even more powerful, but I'm not sure it can get much better than this.

 

[Doug A]

Looks really good @Fandyus. The flash did well, but the lamp has more color.

 

Thanks for sharing,

Doug A

[dabateman]

For a better test you should use the zwb2 in the photo and try the zwb1 on the camera. It will have a deeper uv reach than the zwb2.

I can't figure out the blue plate color with the UVB light vs the UVC lamp you are using, which looks similar to the other lights.

 

[Fandyus]

1 hour ago, Doug A said:

Looks really good @Fandyus. The flash did well, but the lamp has more color.

 

Thanks for sharing,

Doug A

Thanks!

[Fandyus]

33 minutes ago, dabateman said:

For a better test you should use the zwb2 in the photo and try the zwb1 on the camera. It will have a deeper uv reach than the zwb2.

I can't figure out the blue plate color with the UVB light vs the UVC lamp you are using, which looks similar to the other lights.

 

For sure, problem is that the ZWB1 has oxidized slightly and has some weird spots on it, I can't clean it even after I've soaked it in hydrogen peroxide for days. Also if I use it with just the QB39 it leaks IR. I'd need a second one. But now that I have a good deeper UV source I should probably get a second one.. and some cerium oxide.

And now that you mention it, yeah it is really weird that the UVIR won't show the same blue as the UVB light did. Maybe it has to do with the fact that the UVIR does not have a continuous spectrum in UVB opposed to the UVB light? Just a guess.

[colinbm]

My brain is hurting.
When I photograph with UV light with the PTFE in the scene, the PTFE is way overexposed to get a decent picture ?
I think you are showing too much contempt of the dangers of UV exposure ?
Otherwise the examples look good, thanks for showing them.

 

PS, Phosphoric Acid can be used to remove stubborn corrosion off the ZWB filters then followed with Hydrogen - Peroxide.

[Fandyus]

12 minutes ago, colinbm said:

My brain is hurting.
When I photograph with UV light with the PTFE in the scene, the PTFE is way overexposed to get a decent picture ?
I think you are showing too much contempt of the dangers of UV exposure ?
Otherwise the examples look good, thanks for showing them.

I don't think I did anything particularly dangerous here. I don't plan to do this often so even if the discharge lamp actually had UVC, I doubt it could do any significant damage. I wore eye protection so that's taken care of too. And with the UVB lamp, again, reptile forums said that there are people who are exposed to them short term and nothing bad happens, afterall, UVB is in the sun so I'd be damned if I didn't have some natural resistance to it. Plus I don't point the lights at myself, and the environment reflects little UV. As of now, none of my skin is even irritated, not even my hands. And keep in mind people were exposed to the UVIR for minutes at a time and I suspect they didn't get sunburnt either which if they had UVC damage they would. I get that safety was disregarded back in the day but this machine is not Victorian thankfully, so it's probably semi-safe. I doubt it would've sold well at all if it gave you instant sunburn, which it would if it was UVC.

 

As for the overexposure in PTFE, I process the images in darktable with almost all modules turned off which usually renders the image as flat as possible, if that won't help you, you know what to do, expose less. I'm not sure which camera you use but my a6000 has more than enough dynamic range do cover it.

[colinbm]

Just more contempt, you are just not getting it, This forum is full of warnings, unlike other 'red neck' forums.
Melanoma doesn't happen over-night it is a long term damage.

[Fandyus]

2 minutes ago, colinbm said:

Just more contempt, you are just not getting it, This forum is full of warnings, unlike other 'red neck' forums.
Melanoma doesn't happen over-night it is a long term damage.

What redneck forums are you talking about?

Yes, long term damage, I don't plan to ever expose myself to this long term, you can be sure of that.

[Andy Perrin]

I don't know, notwithstanding that sunburns take a day or so to develop, he's probably right that if he didn't notice any reaction then the exposure was probably minimal. Still, these things do accumulate over time. It's the lifetime exposure that matters in the end.

Quote

UVB is in the sun so I'd be damned if I didn't have some natural resistance to it

Ah, yes, people tan sometimes, although that doesn't mean you aren't getting damage and accumulating mutations.

[Fandyus]

I honestly don't want this to become another safety debate. I checked the safety thread, it said it's necessary to wear eye protection, I did that. I don't plan to run this every day, not even every week, maybe once every few months.

I'm definitely willing to make further steps if I want to use the UVB light often. Like sunscreen and cotton clothes. This was a test.

[cazza132]

Thanks Fandyus for putting this together. Very interesting indeed. I like the colours with the Repti Planet UVB 15.0 compact fluorescent bulb.

[Andrea B.]

Fan, thanks for this experiment. It's a good one.

 

And it is useful (to me anyway) to see the raw colors, so thanks for that too.

 

I think that I'm surprised (or something) that the Speedlite scene is that much different from the others. Or, alternately, that the 365nm UV-Led torch scene is so much like the UVB scene. 

 

I think you are aware of the dangers of the shorter UV wavelengths. Col is just trying to be protective of you.  Although I do think that folks forget that UV damage is cumulative over time. This is why almost every senior citizen has to have cataracts removed at some point. 

 

Do you think that there is more UVB in the tanning lamp than there is in natural sunlight? 

 

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For sure, problem is that the ZWB1 has oxidized slightly and has some weird spots on it, I can't clean it even after I've soaked it in hydrogen peroxide for days

 

Yeah, this happens. Sometimes the filter is ruined, can't be recovered. I have lost a couple of blue-green filters over time. It requires a vigilance about routine cleaning which seems to escape me! If I were more careful/digilent/vigilant/whatever, then I would set a computer or phone event to warn me every 6 months to check the danged blue-green filters. 

 

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Phosphoric Acid can be used to remove stubborn corrosion

 

Do you mean the real phosphoric acid or the phosphoric acid in Coca-Cola??

The actual phosphoric acid is rather harmful to skin. Be very careful if using it. The disposal of used phosphoric acid is what troubles me. Is it safe to just pour it down the drain? I don't know.

 

Sometimes the filter corrosion can be removed but it has left "scars".

 

It actually hadn't occurred to me to try Coca-Cola for removing filter corrosion. Hmmmmm.........

The main side effect with Coca-Cola would be stickiness from the sugar. So maybe use Diet Coke. 

Anybody have an oxidized filter to try this out and report back? 

 

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When I photograph with UV light with the PTFE in the scene, the PTFE is way overexposed to get a decent picture ?

 

If we expose for the PTFE, then much of the UV-absorbing areas are too dark.

If we expose for the UV-absorbing areas, then the PTFE is blown-out.

This is because our cameras do not have a wide enough dynamic range to handle both at the same time.

 

The better cameras permit over-exposure which can be pulled back without harm to the rest of the scene. It's called "exposing to the right". The camera is said to have "headroom". It requires experimentation to determine how much headroom your particular camera has. With a Nikon D850, for example, I have usually 2 full stops of headroom. When pulling back the over-exposure, I use a tool which works only on highlights, not on the entire scene. 

 

Alternately, the PTFE is photographed separately using an exposure made on it. Then the other scenes are photographed with exposure tuned to the darker areas. Then you capture the white balance on the properly exposed PTFE and save it as a preset to use on the other files.

 

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I wrote some of this for anybody who is a bit new to UVP and might not know some of it. If you already know this stuff, then kindly ignore. 

[Fandyus]

And thank you! I'm glad you like it.

 

I included the raw colors partially because I know that it is what you do, so I thought you'd be interested.

 

I suspect you mean the raw colors are the same? Yeah that is surprising, but I don't know, the colors with UV are often weird. I suspect that the color for the speedlite is so different because the speedlite actually has a lot of light at around circa 390nm, unlike the other sources.

 

I am generally really surprised by how good the UVB bulb looks. It adds way more saturation to the images, and I must say, I tried to isolate the green channel and it looked a lot like one of those monochrome UVB images that we sometimes see here.

 

I am glad you're not mad at me as well, I know you take safety seriously and I was a little concerned if you'll be ok with me doing this seeing as you're the co-admin of this site. I outlined my reasons for not wearing full cotton overalls in my previous comments, and I think I didn't think wrongly, no skin irritation or sunburn followed, even now that it's been a while. I would use proper protection if I actually was in a situation where the lamp has to be pointed at me, of course. The tanning lamp probably has more UVB, so does the reptile lamp. But I don't know, it would be great if someone with a spectrometer could verify it, but I don't have one unfortunately. But I would assume so due to more violet showing in the pictures taken with it, akin to more violet showing when a deeper UV pass filter is used. But I know wavelength can't be determine through color.

 

I guess I will be ordering the cerium oxide. I also have a ZWB3 that is basically completely ruined, the surface is matte and there seem to be streaks inside of it, I would try to polish that too. I am not sure if the streaks are inside, hopefully not. I'd be willing to try Coca-cola but I am dieting and generally have developed an aversion to soft drinks now, so I would have nothing to do with the rest of the bottle. But I guess there's always someone out to drink this stuff. Diet coke could work as well and I could actually drink it but the artificial sweeteners they use are really bad. I try to consume as little as possible (though I do, mainly in protein shakes and puddings).

 

Thanks for the long comment!