How to recognize 365-370nm UV LED Light + Exposure energy?

[carpenter]

I ordered a 20W UV LED 365-370nm from China.
The diode arrived today
The LED is 20W, i.e. it contains two rows of 10 diodes each
In the picture, approx. 200mA flows through it at a voltage of 32V 30% from 20W .
Photographed in the dark-
The LED shines quite intensely white, as you can see on the banknote in front of the LED, there is some UV there, see the blue glowing fibers
The intensity of the white surprised me. is it normal or did the Chinese intentionally or unintentionally make a mistake and send another definitely noticeably cheaper LED?

I want UV LED to expose Photopolymer Dry Film, for which the manufacturer recommends ´350-380nm UV Light-
Manufacturer recommends Exposure energy 50 mJ/cm2). There is no datasheet for LEDs from China, does anyone have an idea of what energy is actually emitted from a 365-370nm LED at 20W so that it can be calculated Exposure energy i.e. exposure time

 

[dick_freebird]

UV LEDs I have, are a purple that makes your eyes hurt. Not that
you are supposed to look at them. White, they sure as any of the
Chinese hells are not.

However digital photos are not to be trusted as UV might well
"white out" all 3 color sub-pixels if those filters don't block UV
really well. One photon above bandgap energy is as good as
another, if it gets past the fence.

 

[KlausST]

Hi,

Do you recognize it as "white" or is it only on the photo?
Photo: it´s quite normal that cameras detect IR. They see what your eyes can´t see.

Again: lookin into the beam - even if it seems dark or not dangerous - it may hurt your eyes. 20W is a lot!
Be cautious! I recommend to wear protective eye glasses.

Klaus

 

[FvM]

Testing exposure time is the best way to check if the LEDs are emitting UV light. Presume you don't have UV detector or spectral photometer.

 

[carpenter]

see that we have quite contemporary ideas and experiences.
For years I have had a UV light unit consisting of 9 pcs 3W UV LEDs, I have already forgotten what the spectrum is, but it is higher than 365nm. And yes, with these diodes, the visible light is blue-violet and unpleasant.
It's logical, the human eye sees a spectrum of 380 - 760nm. At 380, that unpleasant purple starts, which turns into blue-violet, through blue to blue-turquoise, someone around 500nm.
LEDs in the extreme areas of light never emit in a narrow spectrum where they have a maximum, but they always have an overlap, even if at a lower intensity, therefore the closer UV LEDs are to 380nm, the more they glow in purple or blue.
Here I would like to remind you that white light, i.e. white, is created by mixing the entire visible spectrum.
That's why I was struck by the fact that the 365-370nm LED is unmistakably white. The white one I see with my eye is not a matter of the camera.
I took the photo only after I was "scared" by the white light from the LED.
It is somewhat difficult to estimate the intensity of the white, but if the LED in the photo consumes 6W, then the same white intensity can be achieved with a LED flashlight with a 1W cold white LED.
I took the photo with my mobile phone, but I would say that it quite realistically describes what I saw with my eyes.I also have a digital SLR camera with classic lenses and quite expensive UV filters for them, but I have these toys in the second house
My first reaction was something like a Chinese bastard sent a cheap LED somewhere around 400nm, they cost around $6 even in 20W, 365nm $20. After we calmed down, he wrote a question on edaboard.
I did some searching today and found this.
It's directly from the seller's website of that LED, 365nm really looks like the most white and beats the LED closer to 400nm the more the light is through violet to blue.
Conclusion, I still find it strange, but I have calmed down a bit and will leave the Chinese man alone for now. I'll probably try to expose the UV dry foil and see the result.

 

[BradtheRad]

'Headache in back of your eyes' describes the symptoms of looking at UV too long. It happens to an arc welder soon after operating even briefly without dark goggles. The ache lasts several hours. We get a similar effect from a long sunny day on the beach or snowy expanse, if we don't wear sunglasses.

Sunlight contains UV and overmuch exposure causes our skin to redden. If you dare to test the LED on yourself, hold it close to your arm for a few minutes. It's like being in a tanning booth. (If you look at it, don't watch for long.)

The blue fibers fluorescing is a good sign. Evidently they're a substance that is stimulated under UV light to emit a different wavelength in the visible spectrum. You might find other items in your house that do the same thing. Example, dust seems to stand out bright white under my 15W UV lamp.

 

[betwixt]

Not a very technical idea but I keep a broken (as in not lighting up) LED lamp, the kind with several yellow strip 'candles' rather than SMD LEDs. They glow bright orange in the presence of UV light. No need to remove them from inside the glass but if you do, they make excellent low power strip lights. They need about 70V at 5mA for full brightness.

Brian.

 

[dick_freebird]

If you want to cure epoxy then UV-C bulbs might be the ticket,
I've got some for A/C duct install that are high power and legit]
UVC wavelength.

White LEDs use an emitter in the blue or shorter wavelengths
and the phosphor can respond to blue in many cases. Whether
the wavelength is short enough to cure epoxy comes down to
the base die, and you probably don't get to know that.

Thought, on reading this post originally, about how I could
make a crude spectrometer using a series of different-
wavelength LEDs as stepped-wavelength-threshold
photodetectors. Like if you want to know whether UVC diode
is really UVC, look at a LED in the UVB range to see if it is
pulling photocurrent or not. UVB, use UVA; UVA, use violet...

Direct from manufacturer, through a legit distributor, you
can trust specs. Off eBay, put your (dis)trust in human nature.
And read the whole listing, because I often find that the title
says one thing that's cleverly disclaimed down at the bottom.
Especially when you think you're going to find a bargain on
something leading edge and not mainstream (like UVC LEDs).

 

[carpenter]

I had some time over the weekend so I finished testing the LED.
Probably the most important knowledge.
.The ratio of visible and UV lights is converted depending on the voltage on the diode.
At 3,2V/LED, LED generates more visible light than at 3,4V.
In other words, the intensity of white is growing with voltage, but the intensity of UV grows to a rolling more.
At a voltage of 34V (3.4/LED) 13W, the UV intensity is such that the oscilloscope screen on my desk glowed (I have a digital oscilloscope, but with a classic green screen).
I have a florescence layer of strontium aluminate, europium and dysprosium on the watch hands. It glows bright light blue in UV and green even without UV, 1s of illumination is enough for 30s of intense green in the dark.
Even if I observe only the reflected radiation, the tired eyes effect described here will quickly appear
In conclusion, it is a UV LED and due to the absence of violet and blue, it is probably an LED with a maximum in the 365-370nm band.
I bought here.

I still want to test the LED with a blue dry film, but first I have to find a suitable test pattern to test exposure time and resolution.

 

[KlausST]

Hi,

At 3,2V/LED, LED generates more visible light than at 3,4V.

LEDs should be driven by a current (source). You should not drive them with constant voltage, because it might cause unpredictable current. Very likely you operate them beyond specified limits .. and even kill them.

Talking about "driving voltage" is almost meaningless.

Klaus