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

[Stefano]

Should I put a warning on my initial post? Of course I don't encourage anyone to do what I did.

[Andy Perrin]

Yeah, and don’t direct UV at body parts anymore! Goodness knows, lots of us here have pushed the safety limits a time or two but there isn’t any useful purpose to it in this case. We won’t learn anything new, and cooking our membership is frowned on.

[Stefano]

Better now?

[Stefano]

Andrea will have a lot to say!

[Cadmium]

Stefano, I simply don't see any point in focusing the LED.

What would make sense, is to get a Convoy S2+ 365nm UV Nichia LED torch, and compare the beam of each in the same shot.

That would show you and everyone something.

The beam, the intensity, and the peak and range of the light are all important and interesting.

Myself, I don't like focused beams, they can be used, but for most UVIVF photography situations (what we 'focus' on here) we generally have to 'paint' with a focused beam to illuminate the shot evenly,

so using a torch or light source with a non-focused beam can work much better.

 

Here would be a very good test comparison,

Your LED and a Convoy side by side, point at some fixed even target, first remove the parabolic reflector from the torch to render it non-focused.

Of course, this still tells us nothing about the actual peak and width of your Cree/LG LED emission. You would need to scan that, like John, Ulf, and Jonathan can do.

 

Stay safe.

[Andy Perrin]

I am actually rather curious what it would do diffused rather than focused. That is plenty of power, with a diffuser you would still get a good bit of light...

[Stefano]

I think that (apart from turning paper to ash), if you focus this LED into that 5° beam, you can point it at a distant target and have an even illumination, not only in that plane, but also "back and forth", in the 3^rd dimension. I took some photos in that beam, 4.6 m away (40 cm spot size).

[Andrea B.]

Andrea will have a lot to say!

 

:lol:

We are all adults here. I can only hope that people are sensible about eye protection.

 

*****

 

I am wondering what such a strong UV-LED is used for?

[Andrea B.]

Stefano, in Post #1 of the following link, I made some calculations about safe exposure length for a Blak-Ray lamp.

Perhaps, as a learning exercise, you could make similar calculations for your UV-LED?

In the post somewhere sunlight irradiance is mentioned along with a reference.

 

https://www.ultravioletphotography.com/content/index.php/topic/1539-uv-safety-uv-and-your-eyes-uv-safety-reference/

[Andy Perrin]

I am wondering what such a strong UV-LED is used for?

*villain voice* "That depends on you, Mr. Bond. Give me the briefcase, or the girl gets the LED."

[Andrea B.]

[Stefano]

Stefano, in Post #1 of the following link, I made some calculations about safe exposure length for a Blak-Ray lamp.

Perhaps, as a learning exercise, you could make similar calculations for your UV-LED?

In the post somewhere sunlight irradiance is mentioned along with a reference.

 

https://www.ultravio...fety-reference/

Assuming a UV irradiance value of 4 mW/cm² under sunlight, 4 W of optical power from my LED and a viewing angle of 70°, we have the following:

• At almost exactly 10 in (25.48 cm to be overly precise) from the LED the UV irradiance has the same value you find under sunlight. If this isn't impressive enough...
  
• At 1 in (2.5 cm) you have 100 times the irradiance under sunlight (inverse-square law).
  
• According to Columbia, you must not exceed 1 mW/cm² for periods of greater than 1000 seconds. You have that value 20 in (51 cm) from the LED.
  
• On the surface of the chips, there should be in excess of 50 W/cm². That's 12500 times more than in sunlight, and about 1/9 of the value you find on the SURFACE of the sun.
  

Impressive what semiconductors are capable of today!

[Stefano]

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.

It is actually 2-3 times more.

[dabateman]

Assuming a UV irradiance value of 4 mW/cm² under sunlight, 4 W of optical power from my LED and a viewing angle of 70°, we have the following:

• At almost exactly 10 in (25.48 cm to be overly precise) from the LED the UV irradiance has the same value you find under sunlight. If this isn't impressive enough...
  
• At 1 in (2.5 cm) you have 100 times the irradiance under sunlight (inverse-square law).
  
• According to Columbia, you must not exceed 1 mW/cm² for periods of greater than 1000 seconds. You have that value 20 in (51 cm) from the LED.
  
• On the surface of the chips, there should be in excess of 50 W/cm². That's 12500 times more than in sunlight, and about 1/9 of the value you find on the SURFACE of the sun.
  

Impressive what semiconductors are capable of today!

So for a very short time, before you melt your camera, you get really good UV exposure times.

If we existed in Flash time, could be useful. But since as far as I know the Flash is only in the DC universe, not very helpful to photography.

[Andy Perrin]

So for a very short time, before you melt your camera, you get really good UV exposure times.

If we existed in Flash time, could be useful. But since as far as I know the Flash is only in the DC universe, not very helpful to photography.

I don't know, with a good diffuser on there it might be okay. That would lower the intensity quite a bit by spreading the light around.

[ulf]

I don't know, with a good diffuser on there it might be okay. That would lower the intensity quite a bit by spreading the light around.

The power from a Power LED like this with its normal integrated lens only is spreading the light quite well, with a beam angle of 60° and will very soon have less power density than one Convoy S2+ with its focussing reflector at normal working distance.

To be compared with this setup that likely emits more than double the power:

https://www.ultravio...dpost__p__33849

Even this bundle is less dangerous than a convoy with intact reflector at some distance as it lacks hotspots from the reflector's more beamed light.

 

The main problem with the power-LED is to play around with focussing lenses, locally reaching very high power densities in an uncontrolled way.

[Stefano]

Cadmium (Steve) sent me a Convoy S2+ torch with his U-340 filter to do a comparison with the LED I have. To have fair results, I filtered my LED with a 2 mm thick ZWB2 and a 3 mm thick ZWB1. WB set on the unfiltered LED. The battery in the torch was fully charged, and I ran the LED at 1.3 A. LED on the left, torch on the right.

 

In the next three images, both the LED and torch are at 20 cm from the wall.

 

LED unfiltered:

 

LED filtered with 2 mm thick ZWB2:

 

LED filtered with 3 mm thick ZWB1:

 

In the next three images, the LED is at 20 cm from the wall, but the torch is at 60 cm.

 

LED unfiltered:

 

LED filtered with 2 mm thick ZWB2:

 

LED filtered with 3 mm thick ZWB1:

 

Fluorescence on paper, taken with my phone. Both the LED and torch at 8 cm from the paper sheet (I think my phone auto-adjusted the brightness, the brightness of the torch changes between the images).

 

LED unfiltered:

 

LED filtered with 2 mm thick ZWB2:

 

LED filtered with 3 mm thick ZWB1:

 

Tell me if you want other tests.

[Andy Perrin]

This would seem to confirm Ulf's comment above -- the Convoy is more intense when you don't have focussing lenses to turn the LED into an ant-killing machine. Or a Stefano-killing machine as the case may be.

[Stefano]

Can it kill me?

[Stefano]

It isn't that different from a magnifying glass under the sun when used with focusing lenses, except for the much higher UV content.

[Andy Perrin]

I was kidding/exaggerating, but honestly stop taking chances all the time or SOMETHING will get you.

[Stefano]

Can you imagine building a 40 W torch with 4 of this LEDs (16 chips) all close together with a parabolic reflector and without lenses on top? A bunch of lithium-ion batteries would be enough. It would be so powerful! I don't want to build it, I am just letting my fantasy run. But maybe one day...

[Stefano]

Do you like high irradiance?

 

He concentrated 100 W of blue light into approximately a 5 mm*5mm square, achieving 400 W/cm². I "only" reached 10-15 W/cm² with my LED.

[Cadmium]

I would like to see the two LED's compared along, no lens, no reflectors, just the LED's, and maybe with only the filters added.

Just an idea, not important or required.

[ulf]

I would like to see the two LED's compared along, no lens, no reflectors, just the LED's, and maybe with only the filters added.

Just an idea, not important or required.

It would be interesting to check the intensity for different distances between the LEDs and the illuminated area.

The size of the illuminated surface for different distances is interesting too, to get an idea of the coverage of some subject without light-painting.

 

I think this comparisons can be done by observing and comparing the intensity of the fluorescence of a big sheet of paper.

That light would likely be much stronger than any visual leakage from the LEDs, making filters on the LEDs not needed.

 

It is a pity that you cannot produce RAW-images.

That would make the comparison easier as the intensity information would not have been non-linearly compressed by the gamma.