There was an UV Led lying around, I wanted to check bank notes with it. I soldered a 3W led on PCB. And powered it with 4 AA batteries (connected in series)

The light was bright and purple. (I mean, visible)

So I guess that wavelength was not small.

Because of my ignorance; I touched the LED to check if it was overheated (and it was), and looked directly at it. I do not have any sight issues for the moment, but what I read on internet made me fear.

Is there any possibilty that my finger got harmed? Does visible violet LEDs cause any illnesses such as skin cancer?

By the way, the exposure and the contact (I touched the LED) lasted both approximately 20 seconds.

Thank you in advance.

  • 3
    \$\begingroup\$ I don't think you have really harmed yourself. But if you have any doubts it's better to ask doctor, not electrical engineers.. \$\endgroup\$
    – Eugene Sh.
    Mar 18, 2015 at 21:34
  • \$\begingroup\$ Curiosity kills the cat. And by the way; is a led like this one: (image.dhgate.com/albu_277624365_00-1.0x0/… ) 3 mW or 3 W? \$\endgroup\$ Mar 18, 2015 at 21:37

3 Answers 3


You're fine.

Don't do it again.


UV can be described by dividing it into three categories based on wavelength. UVA, UVB, UVC. UVC doesn't make it through the ozone.

UVB is well recognized for causing suntans, sunburns, skin aging, and of course cancer.

UVA is more prevalent throughout the year, and has been thought to be less important in the formation of skin cancer until more recently. It is now thought that UVA may also play a role in skin cancer, but whether alone or if it has to be in combination with UVB is still being investigated. However we now recommend all patients use a sunscreen that includes protection for both UVA and UVB.

There are others who may be able to correct me, but my understanding is that UV lights produce UVA only, so you don't need to worry about skin cancer. Also, skin cancer risk is related to length of exposure (very short in your case) and is increased with burning versus tanning. Since you didn't get a burn on your finger, your chances of skin cancer due to touching that LED is pretty much zero.

The risk to your eye is much harder to asses. There is the potential for damage to show up many hours after exposure. Again I suspect that you are OK, but I would get an exam from an optometrist or opthomologist to be safe.


If your finger was harmed it will probably form a blister within the next day or so, as if you had touched a hot stove element. Any latent damage that could lead to cancer it's too late to do anything about anyway, so just don't do that again.

Your eyes could indeed have been harmed, without your being able to easily notice it. As far as I know, only a competent opthalmologist will be able to say for sure. You might look specifically for an opthalmologist who is experienced with laser eye safety exams.

  • \$\begingroup\$ Thank you very much. Is a LED like this really dangerous? (Light was bright purple) image.dhgate.com/albu_277624365_00-1.0x0/… \$\endgroup\$ Mar 18, 2015 at 21:38
  • \$\begingroup\$ It's powerful enough to hurt you if you aren't careful. But realy you were probably not hurt if you didn't get your eye very close to the LED or use any lenses to focus light from the LED into your eye. But I am just some guy on the internet. If you are concerned you should consult with a physician. \$\endgroup\$
    – The Photon
    Mar 18, 2015 at 21:51
  • 2
    \$\begingroup\$ Incidentally, the purple light is just the "tail" of the LED's spectrum. If it's a UV LED, there's much more power in the UV where you can't see it. \$\endgroup\$
    – The Photon
    Mar 18, 2015 at 21:53
  • 3
    \$\begingroup\$ And because you can't see it your iris won't contract in order to reduce exposure, which is why it can lead to blindness. \$\endgroup\$ Mar 18, 2015 at 23:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.