13 replies to this topic

[colinbm]

I purchased a UV 10w Germicidal Sterilizer Lamp LED UVC, to test.

The lamp that they sent had no marking or brands as shown in the ad.
With the extra precautions of covering myself up & protecting my eyes, I went ahead & tested the lamp.

When I turned it on the room had a nice ice blue glow, not unlike a 6000k cool white LED light.

Placing my 250-850nm spectrometer in the light confirmed the spectrum of a cool white LED, but NO spectrum below 400nm down to 250nm.
So what is going on, this is supposed the be a UVC lamp ?

Strangely, to me the lamp wasn't 6000k BUT 1750000k instead. So wow what is going on ?

Feeling ripped off, I went to my UVC fluoro lamp & placed the spectrometer in the light & there was the familiar 254nm spike, & low & behold I read 1750000k colour temperature.
I smelt no ozone either.

So what could this lamp be producing ?

[Andy Perrin]

1) You could try the banana test?
2) Ozone production starts significantly below 250nm, I think? So possibly it is not making much ozone. Or you just didn't notice it for some reason like good ventilation.
3) Sure sounds though like you got a fake UVC bulb that is just a white LED with the same color temperature as your real UVC bulb.

[dabateman]

I currently don't trust any UVC LED. If it says that its using leds, I will immediately assume it to be fake until proven otherwise. They are still just far too expensive.
If you want UVC, it has to be Mercury or Krypton bulb.

A LED at 265nm needs to be made from aluminum crystals with a sapphire lens. Currently even at large scale still too expensive.

[colinbm]

Thanks Andy & Dave, but why do I get a reading of 1750000k ?

[UlfW]

At 12 AU$ it is extremely unlikely, (very close to zero), that you get a lamp with 36 or more UV-C LEDs
https://www.ebay.com...27/143662168983

The lamp is producing a visual light that mimics the visual part of a UV-C low pressure tube.
I guess that the transparent part is made of some kind of plastic.

Edited by UlfW, 22 February 2021 - 06:24.

[Andy Perrin]

If you physically hit the germs with the lamp, then it will be "germicidal" I suppose. But it sounds like that's the only way to make the ad copy correct.

The only good thing about stuff like this is that fewer people will be giving themselves cancer with the real thing.

This is an excellent illustration of the fact that the "color temperature" of a lamp does NOT tell you its spectrum. It is only a measure of similarity to a blackbody.

Edited by Andy Perrin, 22 February 2021 - 06:36.

[colinbm]

Yes Ulf, The lamp has a clear plastic cover, but it has cuts / openings from top to bottom.
I broke off a piece of the clear plastic & it cuts the UV below the 365nm line in UVC Fluoro lamp.

Yes Andy, it dongs the bugs well, but some fit between the gaps in the clear plastic cover....

Edited by colinbm, 22 February 2021 - 06:58.

[dabateman]

Lets also think about output. A 15W Mercury 254nm germacidal bulb might be 30% effective. There is heat loss and losses at the ballast. So the output is really is about 4.5W best maybe.

Now real 265nm LEDs are about 20 to 60 mW at best output. I have a feeling that the cheaper ones are driven hard with more heat loss (to burn that green banana) and may result in more doublet 530nm light production.

So I think you have mostly an expensive inefficient 530nm light source mainly.

But if working with real 265nm leds you will need at least 225 of them to equal the output of a now $20 15W Mercury 254nm bulb. So really not worth it. A year ago a 25W bulb was $15, but then COVID made these more expensive.

Your Led bulb looks to have about 60 leds.
Now if real, then it will be about 1W, so expect a quarter of the output of a 15W germacidal bulb at best.

Edited by dabateman, 22 February 2021 - 08:53.

[Stefano]

You would need between about 450 and 560 of my 265 nm LEDs to have 4.5 W of UVC. At 1 W input power each, that would equal 450-560 W of input power, and that's a lot to dissipate (it becomes almost all heat).

David, why do you think these LEDs produce 530 nm (double 265 nm)? They don't work like lasers (you can double 532 nm lasers to have 266 nm), the visible light they emit is due to self-induced fluorescence as far as I know. It isn't necessarily at 530 nm, it actually looks bluish usually.

A spectrometer might see 530 nm because of how gratings work (second-order diffraction), and that is probably what the guy in the video in this topic saw.

[dabateman]

Yes my background is microscopy and spectroscopy, so I jump to thinking second order harmonic even when it may not apply.
I am still getting my head around the gap junctions used to generate light within an LED.

[Stefano]

dabateman, on 22 February 2021 - 13:49, said:

I am still getting my head around the gap junctions used to generate light within an LED.

I am still impressed we can make semiconductors with bandgaps of 4-5 eV. It is a lot.

[Stefano]

About the crazy high color temperature Colin measured, it is odd since past a certain point (like 100,000 K) the hue doesn't really change much. As the temperature grows, the color tends to a specific shade of bluish-white, and at infinity the color is still that bluish-white. It "converges".

Here you can see it: https://en.m.wikiped...nckianLocus.png

Notice how the curve tends to a specific point at infinity. In the real world, an object heated at that temperature would get extremely bright, to the point where it would set fire to nearby objects, and the color would tend to that precise hue.

[colinbm]

Thanks for the explanation Stefano

[colinbm]

Andy Perrin, on 22 February 2021 - 05:35, said:

1) You could try the banana test?
2) Ozone production starts significantly below 250nm, I think? So possibly it is not making much ozone. Or you just didn't notice it for some reason like good ventilation.
3) Sure sounds though like you got a fake UVC bulb that is just a white LED with the same color temperature as your real UVC bulb.

It failed the green Banana test, with no marks.