Since UV lights are important to reptiles, and I've heard it said that they lose their UV output after about 6 months even if they haven't burnt out, is there a way to measure the UV output of a light? That way I can get the most out of my UV lights, only replacing them when the UV output stops.

  • It's pretty complex to measure actually, though devices exist. Typical tubes emit more from the end then the middle and so the reading won't be consistent or constant.
    – Joanne C
    Commented Feb 24, 2014 at 20:54
  • 1
    Anecdotally, I've found that there's a hint of visible blue light present when they are brand new that tends to fade away slowly. I just usually go by the 3-6 month time course that you've described.
    – jonsca
    Commented Feb 24, 2014 at 23:15
  • UV photodiodes themselves aren't very expensive (say $20) but most of the ready-to-go complete devices I've seen tend to be over $500.
    – PeterJ
    Commented Feb 25, 2014 at 1:21

1 Answer 1


These lights/tubes produce UVA and UVB. The same type of tubes are used in sunbeds and marine tanks

To produce UVA, mercury inside the tube reacts with the gas and electricity. This is why you should never shatter tubes because you can get mercury poisoning and they have to be disposed of properly. The mercury will slowly stop to react as expected - as a result, the tube will produce more UVB. We do not need UVC to be emitted from the tubes because in nature most of UVC from the sunlight gets stopped by the ozone and atmosphere. UVC is used in germicidal lamps and has no benefits to living matter.

This is very noticeable in the sunbed sector, when old lamps start to burn skin instead of tan. It is very unhealthy for all living things as it directly damages DNA.

To accurately measure the tubes you need a UVA and UVB meter. Usually sold separately and cost in the region of 100USD each for low quality ones. Anything cheaper is junk that just makes up numbers.

If you run your tubes/lights 8 hours a day then it is typical to replace them after 6~8 months, as this will keep your animals and or plants much healthier. You will be better off investing the money in new lights rather than in testing equipment you will use a few times only.

  • 1
    Hi, I didn't want to change your intent from the original version "we do not need UVC because most of it gets stopped by the ozone and atmosphere" so it's ultimately your decision if you want to modify it in your answer, but actually all UVC part of the spectrum gets completely blocked and none of it reaches the ground (and for comparison, most of UVB gets blocked and most of UVA passes through) source.
    – lila
    Commented Feb 8, 2021 at 23:11

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.