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UltravioletPhotography

Test of a 365 nm LED on ebay (powerful!)


Stefano

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WARNING

WHAT I DID SHOULDN'T BE REPLICATED OR ATTEMPTED UNLESS YOU REALLY KNOW WHAT YOU ARE DOING, AND YOU WEAR SAFETY GOGGLES AND SKIN PROTECTION.

INTENSE UV RADIATION, EVEN IF IT IS UVA, CAN AND WILL HARM SKIN AND EYES.

 

Hi,

Here I will be talking about a 10 W, 365 nm LED. This LED is efficient, small and VERY powerful. I found it on ebay. The seller claims a 10 W power consumption and an impressive 4-4.8 W power output. That would mean a 40-48% efficiency, which is a lot for a 365 nm LED, although efficiencies of 30-35% have been achieved. The seller also claims that this is an LG LED, and that it has a quartz lens. The lens gives this LED a 60° beam (an LED emits an almost 180° wide “beam” without optics to narrow it). The LED is actually composed of 4 chips, in a 2S2P (2 rows in parallel each composed by 2 chips in series) configuration.

Having said this, this LED produces a LOT of UV light. The seller recommends a forward current of 1-1.4 A, and I usually run it at 1.3 A. The LED is saturated at that current. I tried to run it at 2 A, and the output pretty much stayed the same. It requires 7.5 V to pass 1.3 A in it, so the power consumption is 7.5*1.3 = 9.75 W, very close to the rated power. As almost all 365 nm LEDs, it emits a bit of yellow-white light, and if you want a pure UV output (you need it for UVIVF, for example), you have to filter it. Needless to say that you need an heatsink to dissipate the (theoretical) 6 W of wasted heat. In my case, since I treated this LED as a “guinea pig” for my experiments, I only attached it to an heatsink with rubber bands, without screws or thermal paste. It still dissipated heat quite well, but you should use thermal paste to do that. I have a new one, still unopened, that stayed in a drawer for months, waiting to be properly attached to an heatsink. I used this LED to burn things, and this is not recommended, since smoke will deposit on the lens, heating it up because of the absorbed light. Even a 5% absorption means 200 mW of power converted into heat on a 5-6 mm lens. When it was new, the lens didn’t heat up (it was cold to the touch immediately after the LED was turned off). Later, it heated up considerably.

So, how powerful is this LED?

  • At 15 cm (6 in), I can feel heat on my lips and face in general.
  • At 10 cm (4 in), I can feel heat on the palms of my hands.
  • At 5 cm (2 in), normal, clean white printer paper reaches 33 °C (91.4 F).
  • At 2 cm (0.79 in), the same paper reaches 80 °C (176 F). At the same distance, normal paper colored black with a black permanent marker on both sides starts to smoke a bit after 5-10 s of exposure. My skin gets pretty warm, and starts to smell oddly (still didn’t understood if something is happening on my skin or it is a chemical released by the LED).
  • At 1 cm (0.4 in), my skin gets so hot that I can no longer keep it continuously at that distance from the LED (and anyway, you shouldn’t do that. I have approx. 2.5-3 W/cm2 of UV at that distance, which is up to 500 times more than UV in sunlight (given a solar irradiance of 1120 W/m2, and assuming 5% of it is UV radiation, from Wikipedia). At this distance paper starts to darken because of the temperature it reaches.
  • At 5 mm (0.2 in), paper starts to burn. The blue dot of fluorescence on paper is too bright to look at. Sometimes paper can ignite (I never got it to light on fire, but it became orange, so combustion was initiated). The calculated irradiance, given 4 W of optical output in a 8 mm wide circle (measured with fluorescence on paper), is 8 W/cm2, about 1400 times more than under sunlight.
  • Anywhere closer, and paper, wood, black tape, and any material which is not very transparent to UV or doesn’t reflect a lot of it, will heat up and burn.

All distances measured from the lens.

Since the LED is a good approximation of a point source of light, given its intensity (a lot of power from a small surface), it can be collimated into a narrow beam. I also like the fact that the lens directs all the light the LED produces into that 60° beam, which can be further collected by a second lens, giving an almost perfectly collimated beam (that, and that’s important, contains ALL the light the LED produces). If the source is infinitely small, you can (in theory) get a diffraction-limited beam, but in my case, since the LED has a non-zero size (of course), you can focus light up to a certain point. In my case, using a car headlight lens, I got a 5° beam. I got a circular, well-defined spot (an image of the lens covering the LED basically), 40 cm in diameter (16 in), 4.6 m (15 ft) away (that’s how I calculated 5°). With the unfiltered LED, I feel heat on the lips 1.5 m (5 ft) away and on my hand 1 m (3 ft) away in the collimated beam.

But that’s not all. I discovered (and yes, I specify this, I re-discovered myself) that, using a second lens above the first one (for a total of three lenses, counting also the lens on the LED), I could re-focus almost all the light emitted from the LED in a spot about the same size as the LED, but ~15 cm away from it. (Notice that you can not focus light into a spot smaller than the light source itself, if you do that without wasting a significant amount of light. Or, better, you can not achieve an irradiance greater than the one you started with. This rule is also valid when you play with a magnifying glass under the sun. No matter what you do, you will always have a lower limit for the spot size, for a given amount of power). This way, I can burn things without damaging the LED (if only I knew that before!). You can burn paper, cardboard, wood, transparent polycarbonate (remember, it is a UV LED) and so on. You can apply this focusing technique to every light source.

While writing this review (it is a review after all) the lens came off the LED. I don’t know if it was due to the extreme thermal excursions or because the glue isn’t strong enough. I even used sandpaper on the lens, before it came off, to remove some dark spots caused by my burning activities, and it didn’t came off. So now I have the opportunity to show how the de-domed LED looks like. If you are going to use parabolic mirrors instead of lenses to focus this LED, you should remove the lens, and, if you can, install a new one that does the opposite of a normal lens: diverging the light to the sides of the LED, leaving a dark spot in front of it.

 

And now for some images...

 

Beam pattern ~10 cm (4 in) away (with lens). You can see that it isn't a perfect circle, but rather a square-circle with holes on the corners. I still like it.

post-284-0-56925200-1583258656.jpg

 

Brighter image

post-284-0-08735300-1583258765.jpg

 

Then I marked 8 points on the paper with a yellow highlighter, to then calculate the beam angle:

post-284-0-39812700-1583259183.jpg

 

Results: 70.5° (left-right, up-down in the image above) and 73.5° (diagonals). So not really 60° as advertised, but still quite close. I put the vertex of the (imaginary) triangle on top of the LED lens.

 

Circular spot of the 5° collimated beam:

post-284-0-62334000-1583259428.jpg

 

LED with lens (don't mind the glue residues on it, it came clean of course):

post-284-0-20938300-1583259564.jpg

 

LED without lens. One of the chips is slightly darker, but that was my fault. If something deposits on it, it will simply burn:

post-284-0-12531700-1583259595.jpg

 

Lens alone:

post-284-0-21502400-1583259624.jpg

 

Using a USB camera with a screwable lens (I can unscrew it completely) I made a sort of DIY microscope, and took some images of the LED chip, turned on at a very low current.

Here you can see that the LED chips aren't perfectly matched. Also there is quite a bit of space in between, but I guess it isn't easy to put them very close to each other.

post-284-0-28104300-1583259855.jpg

 

Even more magnified image:

post-284-0-54109400-1583260017.jpg

 

Very rough drawing of the lenses setup to re-concentrate light away from the LED:

post-284-0-14215200-1583261231.png

 

Setup in real life:

post-284-0-93472000-1583260753.jpg

 

Some burn tests (away from the LED, with the above setup):

post-284-0-08290900-1583261424.jpg

 

post-284-0-39071800-1583261347.jpg

 

post-284-0-62508500-1583264548.jpg

 

Burns on wood, putting it a few millimeters from the LED (with lens). The big blob is just black spray paint:

post-284-0-49940800-1583264778.jpg

 

Burn on the same wood (red circle), done far from the LED this time:

post-284-0-39530400-1583265295.jpg

 

Burns on the same piece of wood, close to the LED (with lens), at the (approximate) written distance:

post-284-0-66374700-1583265393.jpg

 

Images of the four chips burned on paper with lenses (far from the LED). LED without lens ("de-domed"):

post-284-0-74785000-1583265651.jpg

 

Polycarbonate goggles, burned far from the LED in a couple of minutes. They were broken, so this is not a waste:

post-284-0-56257500-1583265796.jpg

 

Now I reached the maximum upload size... I will add other details soon. Hope I didn't make any mistakes.

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Link for purchase (I don't have any affiliation with the seller): https://www.ebay.com/c/11026963346

 

I could turn paper brown from 1.5 m away (with lenses). I will add an image as soon as possible. Hopefully this topic isn't too heavy.

 

Edit: I noticed the LED is not the same as it was before.

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Andy Perrin
  • At 15 cm (6 in), I can feel heat on my lips and face in general.

 

That is an impressive LED, but man...anything that can MELT THE GOGGLES is for sure not anything you should be directing at your face!

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Oh dear -- that is surely a dangerous toy to play around with. Please, be as careful as possible. We haven't any member to lose !!
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I wore polycarbonate goggles all the time. They do a pretty good job at blocking UV light (they melted). Of course I needed something close to 15 W/cm2 to burn them.
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Still, 4-4.8 W of output power is a pretty high claim. A high quality LED may be able to do that, but I don't know for sure.
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Andy Perrin
Sure but if you are shooting so much UV that you can feel the warmth on your skin, it's probably not great for the skin! I know the danger goes up for shorter wavelengths, but sufficiently intense UVA can't be great either. Lets just use common sense here.
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Yes, not a very wise thing to do... I think that if you feel heat from the irradiance it means that you are way above the safety limits.
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Just imagine the UV irradiance on the surface of those chips... Let's say they are squares with a side length of ~1.3 mm (roughly measured with a ruler). The area (in cm2) is 0.0169. So, if they emit the claimed 1-1.2 W per chip, we have 59-71 W/cm2. The Sun emits ~62 MW/m2 of radiation on its surface. Having a 8% UV content (outside Earth's atmosphere), that means almost 5 MW/m2, or 497 W/cm2. So, on the surface of those chips, we have 11.8-14.2 % of the UV (A, B and C) on the surface of the Sun. No wonder why the seller claims germicidal capabilities!
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If you have transparent safety glasses, then the blue part of the light of such power can also be very dangerous for your eyes .. especially in the dark.

It may make sense to use yellow polycarbonate glasses or whatever.

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Ninjin, that is an interesting point. I have never heard anyone say that before.

I do believe the yellow (amber) glasses are better than the clear ones.

I personally usually use these glasses, and I recommend them:

https://www.fullsour...om/uvex-s0290x/

 

Stefano, those are very affordable. I have tested them.

They also have the orange version, however, although they block visual light higher than the amber version, my tests show that the orange version has a 380nm+/- leak.

So buy some amber glasses.

However, DO NOT do what you are doing to focus the LED to a spot that burns things, for crying out loud, why are you even doing that!?

Are you trying to shoot down satellites or space stations out of orbit? I would stay away from that, even if you aren't able to focus your beam on your target, you might injure your self, someone else, animal,

or become the target of some investigation.

Seriously, what is your point in all that?

No one uses LED's that way unless they work for DARPA.

You will not use that for photography, we are not here to start fires, or melt things, that proves nothing for our endeavors here.

It just scares people, and it should scare you too.

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Ok. I want to make a point here about safety, and how dangerous shining this thing on your skin is, based on some of your observations.

 

The light source you have is UVA, and while not as damaging to DNA as UVB, it will penetrate much deeper into the skin. This wavelength will be going deep enough to impact elastin and collagen structure and integrity in the dermis. You are likely to be triggering the melanocytes to go into overdrive to produce melanosomes to try and protect your skin. Don't be surprised if you get dark patches on your skin over the next few days/weeks where ever this was shone on the skin.

 

In shining this at your face where the skin is thinner and provides less protection than the rest of the body, these effects will be increased, as the skin there provided less protection.

 

You do not mention how long with was being shone on different parts of your body, but there is mention that at 1cm you couldn't hold it there continuously. Hopefully the exposure was only a few (much less than 10) seconds.

 

You do not know the spectral distribution of the light being produced, but it will be different to the distribution in sunlight (with much more emphasis on the 365nm region) therefore comparing the power density will be misleading, as different wavelengths produce different effects.

 

I'm all for experimenting, and even have at times been known to push the edges of what would be considered safe, but the types of effects you are describing here scare me. I would hate for anyone else to come along, see this and think it is ok to shine high power LEDs against different parts of their body until it feels hot or 'started to smell odd'.

 

Might be worth adding, in bold and underlined, something at the beginning of your first post which states the no-one else should try the parts if this experiment which were shining this on the skin, just to make it obvious for anyone finding this post.

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Hopefully no one else tries this. We should not promote home built UV focused beams to destroy or burn things. Don't be that afraid of drones to build this at home.

 

You weren't wearing gloves. Next time please wear nitrile gloves to protect your hands. You will have localized tanning due to the beam from holding the paper. Monitor those areas closely for burns at least 2 days after these tests.

Never have skin exposed near something like this.

I hope you don't feel nauseous or dissy days or immediately after this exposure.

 

Now drink an excessive amount of water to help your body clear any antioxidant and protection pathways that might have been upregulated. As in you will need to drink more than 10 glasses of water over a day and expect to pee a lot.

Radiation poisoning may not be obvious so at a minimum drink lots of water to clear your system.

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High intensity UV should ALWAYS be treated with respect.

Focussing the light like that can be really dangerous as the local intensity can be very high.

 

The LED used emits the same amount of light as several Convoys bundled together as discussed here some time ago.

That type of LED is used in arrays in industrial UV-curing lamps used to fast cure UV-glue.

Then there are several of these LEDs mounted together demanding massive cooling.

 

The LED itself is interesting as it has a more even light pattern than the Convoy's light-spot created by it's reflector.

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Ninjin, that is an interesting point. I have never heard anyone say that before.

I do believe the yellow (amber) glasses are better than the clear ones.

I personally usually use these glasses, and I recommend them:

https://www.fullsour...om/uvex-s0290x/

 

Stefano, those are very affordable. I have tested them.

They also have the orange version, however, although they block visual light higher than the amber version, my tests show that the orange version has a 380nm+/- leak.

So buy some amber glasses.

However, DO NOT do what you are doing to focus the LED to a spot that burns things, for crying out loud, why are you even doing that!?

Are you trying to shoot down satellites or space stations out of orbit? I would stay away from that, even if you aren't able to focus your beam on your target, you might injure your self, someone else, animal,

or become the target of some investigation.

Seriously, what is your point in all that?

No one uses LED's that way unless they work for DARPA.

You will not use that for photography, we are not here to start fires, or melt things, that proves nothing for our endeavors here.

It just scares people, and it should scare you too.

I did it just because I could and I wanted to have some fun. It is like those multiwatt burning lasers that can light up matches, burn paper, and basically do what I did. This is not risk-free, and I didn't put my skin in the spot while burning stuff. Of course I don't encourage anyone to irradiate skin with 10-20 W/cm2 of UV, since you will literally burn your skin because of the temperature it will reach. I maybe have done this for less than half a second on my fingertips, getting like 5-10 J/cm2 of UVA.
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At 15 cm, I should have 11.5-13.4 mW/cm2, which is 2-3 times less than in sunlight. It surprises me than I can still feel heat from that. At 10 cm I have 2.25 times more irradiance.
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You do not mention how long with was being shone on different parts of your body, but there is mention that at 1cm you couldn't hold it there continuously. Hopefully the exposure was only a few (much less than 10) seconds.

Yes, at 1 cm I maybe held my finger for 1 second. 10 seconds and I would have cooked it.
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Hopefully no one else tries this. We should not promote home built UV focused beams to destroy or burn things.

Yes, that's not the point (that's not how you should use this LED). I tried pushing it to the limits. This LED is very interesting because, being small, it will cast sharp shadows on a subject, and you can manipulate its light a lot. The smaller the light source, the more you can manipulate it (focus, direct in a specific direction, etc.).
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I hope you don't feel nauseous or dissy days or immediately after this exposure.

I feel well for now, thanks.
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