Nichia 033A UV LED: Shiny Metal Test for Visible Output

[Cadmium]

Andrea, Thank you for taking this topic back to your original point. I probably wasn't quite clear what the point was exactly. So I apologize for that.

But now I will disagree once again, an old disagreement I had years back, that spectralon does fluoresce some.

Remember your tests a few years back now I think it was, you had a brick background I think?

So I think spectralon does fluoresce some.

Regardless, I don't think the spectralon is illuminated by the 700nm red that is only seen by the full spectrum camera when pointed directly at the lens, and requires a much longer exposure than otherwise even in direct mode.

I could be wrong, but I tested that years back...

Again, if you had U-340 2mm on the torch, then your leak. isn't violet.

Les, technically it is violet, given the formal definition 380nm to 450nm (I think it is?),

I just say violet/blue because the visual part of violet falls into the blue part of RGB, and it looks blue to.

[Andrea B.]

I have to say that if you shine a Convoy S2+ with 2 mm thick U-340 into your eyes (to me it happened several times briefly, I never do that on purpose and I usually wear goggles), you CAN see UV. It appears whitish violet.

 

Most of us can see something between 380 nm and 400 nm. There is no clear demarcation between UV and Visible (violet) light. By convention most references seem to give 400 nm as the dividing line, but you will often see 380 nm instead. (Why not 390 nm? I don't know but I don't think I've seen 390 nm as the dividing line.) Beyond 380 nm or so, the human eye's lens blocks UV. And the older you get the more blocking you get as the lens yellows with age.

 

Also note that the eye's lens fluoresces, so it might not be clear whether you are detecting UV or lens fluorescence. We need to look up what kind of light the fluorescing lens emits. I don't quite have time right now.

[Cadmium]

Of course what we are all talking about when we say visible violet is above 400nm, yes, we can see that.

Actually U-340 cuts to OD3 at 390nm.

Lets use UG11, because there is more data, UG11 cuts to OD3 at 390nm, and OD5 at 400nm.

 

[Andrea B.]

Spectralon does fluoresce some. Remember your tests a few years back now I think it was, you had a brick background I think?

 

Oh, Cadmium, that was some old paint or whatever on the old bricks which fluoresced and reflected off the Spectralon.

 

You can ask LabSphere whether Spectralon fluoresces. They will say no.

 

Interestingly. because Spectralon is unreactive, non-fluorescent stuff you can add fluorescent material to it to make fluorescent standards. I don't recall what is the dark stuff added to the Spectralon matrix to make the grey and black targets which I use.

[Andrea B.]

Reference to the non-fluorescence of Spectralon: https://www.labspher...rence-phosphor/

More of a mention of the non-fluorescence than a reference, but I'm out of time for this today.

[Stefano]

Well, maybe this isn't the right topic to discuss this, but I will do it anyway. Maybe we should move this discussion elsewhere? I don't know.

 

I know how it looks like when UV makes your lens fluoresce. You see like your eyes are cloudy, you see grey instead of black. Most transparent plastics fluoresce blue under UV. Try to see through a piece of fluorescing transparent plastic, and this is how it looks like. Not a pleasing thing to experience (and, don't forget, not healthy). Putting your goggles on makes you see clear again.

 

A fluorescing lens doesn't make a sharp image. Instead, I see a sharp image. Not only that, it is also focused very differently. Our eyes have a big focus shift between visible light and UV. In UV we are short-sighted, and I have to focus a UV light source as if it was much further away than it actually is.

 

When I tried to do this at 340 nm, running my LED at low power, not only the light appeared blue, but the focus shift was even more extreme. The maximum distance I could focus the LED was ~20 cm (~8 in). Other people have done researches on this, and people actually see UV around 350 nm as blue: https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.quora.com/When-people-can-see-ultraviolet-what-is-the-color-they-see&ved=2ahUKEwiC09r-v7DtAhWBxqQKHVMMA7MQrAIoAnoECBQQAw&usg=AOvVaw0lzc0-RX49k4CvR9VGaD_n&cshid=1606953620504

 

I don't advise anyone to attempt this, of course.

[Cadmium]

It is an old disagreement, not really important right now to me, I tested it, cleaned it even the way they instruct.

I could be wrong, of course, but if you ask me it fluoresces some, of course not as much as almost anything else.

OK, old tests, I have a bunch of these... I should redo them, but I don't really want to jump into that at the moment. I will stop. Sorry.

 

By the way, the black in the background is brown cardboard painted with Krylon Ultra Flat Black Spray Paint #1602.

 

Visual

 

UVIVF

 

UVIIRF - RG715+

[Andrea B.]

I see a sharp image.

 

You very well could be seeing UV better than most. It is not unheard of. And you still have young eyes.

 

I found a nice reference about transmission of UV through the various parts of the eye.

 

Transmission of the Ocular Media

https://iovs.arvojou...ticleid=2122713

by Boettner and Wolter

IOVS, 1962

 

Excerpt:

 

The ultraviolet and short wavelength visible light transmittance varies considerably with the age of the eye. The lensof the young child begins transmitting at 300 nm; however, an absorption band centered at 360 nm reduces the transmittance to a very low value below 390 nm. Because of this absorption band, the lens of a child has a transmitting band centered at 320 nm of about 8 percent under 5 years and less than 0.1 per cent by the age of 22 years.

 

The total transmittance of the young eye begins increasing rapidly about 390 nm and reaches 90 per cent at 450 nm. The rate of increase is considerably slower for the older lens, e.g., a 63-year-old lens begins transmitting at 400 nm but does not reach 90 per cent total transmittance until 540 nm. In addition, the light scattering by the older lens is much higher. The direct transmittance of the young lens at 700 nm is about 88 per cent, while the 75 year lens measured only 41percent.

 

[Stefano]

That's interesting. A very young child should be able to see UVB, and rivals a Kuribayashi. I didn't expect that secondary peak, and also that SWIR peak is strange. Shouldn't water be black there?

 

I also have to say that 340 nm actually appears quite bright to me. I just tried looking at my LED at full power through my UV-pass filter stack for a fraction of a second, and then turned on a 5 mm epoxy ~30° beam blue LED, to a current at which it appeared about as bright. At 0.05 mA the brightness was about the same. The voltage was 2.4 V, the power consumption was 0.12 mW. Assuming 1/3 efficiency, that's 0.04 mW of blue light. They appeared as bright as ~50-60 mW of 340 nm UV, and the beam angle of the UV LED is close to 180°, since it has no lens. If we don't take the beam angle into account, I am 1250/1500 times more sensitive at 450 nm than at 340 nm. This are very rough estimations, they are probably quite wrong, and I didn't take a lot of things into account, but the order of magnitude is about 10³.

 

To give an idea, you know those red/green colored LEDs used as indicators, those with a colored, diffuser lens? That's about how bright 50 mW of 340 nm UV appear to me, maybe a bit less, say half of that. If I put a UV-pass filter on my eye, I can see illumination about 5 cm (2 in) away.

 

Maybe I will stop torturing my poor eyes for a while, that's a good idea.

 

Another edit: when I did this "UV vìsion check", I illuminated a piece of white bi-adhesive tape, and it looked almost black. I now checked with my camera and a 365 nm torch + 3 mm thick ZWB1, and it looked dark. Not black, but dark. I think my eyes have more UV range than my camera.

[Andrea B.]

I was thinking.....

There is transmission of wavelengths through ocular media and then there is actually "seeing" them.

The eye pigments must be stimulated in order for the brain to "see".

 

The window around 320 nm for younger people is interesting.

But there is a lot of absorption until about 390 nm.

 

A very young child should be able to see UVB

Maybe, but there is not very much UVB to see.

Just as happens with our camera sensors, I suspect

that the vastly larger amount of visual light quite overwhelms any UV signals.

 

*****************

Yes, you might want to think about UV eye damage. It is cumulative.

You don't want be having cataract surgery before you are 30.

[Andrea B.]

Fluorescence of Spectralon or Not should be taken up in its own topic.

[Stefano]

Hopefully I will not have cataract surgery so young. Better not to tell my doctor if I will have a vision check in the future.

 

It seems that at 340-350 nm blue cones are dominant. The red ones are no longer sensitive there. So light appears violet only in a well-define region, about 360-435 nm. While in the IR end, there's just dimmer and dimmer red.