What is Uv light: Definition and 48 Discussions

Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight, and constitutes about 10% of the total electromagnetic radiation output from the Sun. It is also produced by electric arcs and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights. Although long-wavelength ultraviolet is not considered an ionizing radiation because its photons lack the energy to ionize atoms, it can cause chemical reactions and causes many substances to glow or fluoresce. Consequently, the chemical and biological effects of UV are greater than simple heating effects, and many practical applications of UV radiation derive from its interactions with organic molecules.
Short-wave ultraviolet light damages DNA and sterilizes surfaces with which it comes into contact. For humans, suntan and sunburn are familiar effects of exposure of the skin to UV light, along with an increased risk of skin cancer. The amount of UV light produced by the Sun means that the Earth would not be able to sustain life on dry land if most of that light were not filtered out by the atmosphere. More energetic, shorter-wavelength "extreme" UV below 121 nm ionizes air so strongly that it is absorbed before it reaches the ground. However, ultraviolet light (specifically, UVB) is also responsible for the formation of vitamin D in most land vertebrates, including humans. The UV spectrum, thus, has effects both beneficial and harmful to life.
The lower wavelength limit of human vision is conventionally taken as 400 nm, so ultraviolet rays are invisible to humans, although some people can perceive light at slightly shorter wavelengths than this. Insects, birds, and some mammals can see near-UV (i.e., slightly shorter wavelengths than what humans can see).

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  1. aaaaautumn

    A Visualising visible light Fluorescence

    Hi all, I am new to physics forum and would appreciate all your input in this topic. I am trying to understand if an object fluoresces under UV light it is possible it may also Fluoresce under visible light? additionally would it be possible using band-pass filters (device that passes...
  2. K

    Correcting the retrobrite "marble" effect

    Hi all, For those of you are unfamiliar with the concept of "retrobriting" plastic, it involves exposing yellowed plastic to UV light whilst being submerged in some variant of peroxide. This has proven to be effective in reversing the yellowing effect on old plastics. However, certain plastics...
  3. Lotto

    B What happens when ethane absorbs UV light?

    Because when I have two carbon atoms, they create a single bond, so their two electrons are in one boding orbital, but I have also one anti-bonding orbital here. And when the electron excitates from ##\sigma## to ##\sigma^*##, how can the bond between the carbon atoms exist? It has to disappear...
  4. A

    I Focusing UV light from a 275nm LED down to a small spot

    Hello, I'm trying to focus a 275nm (with proper safety precautions) LED that looks to be a few mm in length and width (the light-emitting portion) to a smaller dot size. The LED should probably be fairly close to the surface of the lens to collect more of the light. The dot size would hopefully...
  5. D

    Optical Where to look for a UV light that is invisible to the naked eye?

    Where to look for a UV light that is invisible to the naked eye? Essentially I want to buy a UV light that doesn't have that annoying blue glow, I just want the UV light that is invisible to the naked eye like infrared light. I read a bit about it and from what I read what I'm looking for is...
  6. Furno

    B Is there a material that allows visible light and UV light to pass through?

    Is there a material that allows visible light and uv light to pass through? Edit: A physical material
  7. G

    Question about whether UV light can penetrate a cardboard box

    Does cardboard absorb or reflect UV from indirect sunlight? does it go through the cardboard and hit the plastic and rubber items inside the shoe box with UV?
  8. terminator 87

    Questions about UV light and dry plastic and rubber

    UV causes dryness of plastic and rubber and lights have UV so keeping it in the dark away from light inside boxes prevents this but notice this photo where the box where the arrows are marked the clarity q enters this region of the closed box is enough for the long term the UV of this clarity...
  9. A

    Light intensity at a distance -- UV light to kill bacteria

    I have obtained seeds of a rare rhododendron species. These seeds are contaminated (experimentally determined). While I have tried several common methods, none decontaminated the seeds. Lately, I have read that so many joules of UV light at approximately 254nm will prevent replication and...
  10. Zeynaz

    Does Fluorescent Powder in Tubes Absorb UV Light to Prevent Oxygen Reaction?

    I know that the answer is NO because now there is an extra substance (the fluorescent powder) that is affecting the emission. However, i don't know how fluorescent powder works in this case. I tried to search it up and only found that Fluorescent powder will 'fluoresce' when it absorbs UV...
  11. M

    On Rayleigh Scattering and UV Light Absorption

    I've read that UV light cannot "penetrate" the atmosphere as easily during winter. But what does this exactly mean? My hypothesis is that due to rayleigh scattering, since light with smaller wave lengths scatter more, the UV light doesn't end up reaching the surface of the Earth (i.e. gets...
  12. J

    Materials that allow IR or UV light to pass through?

    Glass allows visible light to pass through I would like to find a list of materials that allows lights of different EM spectrum to pass through, not just the above, Searched throughout google, couldn't find any!.
  13. SW Dad

    UV light + electric current = boom?

    Hi, so I was hoping to get an EE's explanation for what just happened. So my son was apparently over by the light switch pointing a UV pen light at the switch. Suddenly there was very loud, gunshot-like pop, sparks flew, and I had to go reset the breaker. Maybe correlation doesn't imply...
  14. Fervent Freyja

    Are mosquitoes attracted by UV light?

    Are mosquitoes attracted to UV light? This PF thread isn't very clear on whether it does or not- some of it suggests that it does... So, I looked it up and found this article on Wikipedia: The American Mosquito Control association also http://www.mosquito.org/page/faq: Is the information...
  15. ORF

    I Why uranium glass glows green if it's under UV light?

    Hello Why the uranium glass glows green if it's under UV light? The most accurate thing I have found it's a brief history of uranium glass: somewhere it's said the more uranium oxide you put in the glass, the more intense will be the green light when exposed to UV light. Thank you for your...
  16. D

    Best way to calculate UV-Vis absorption onset?

    Homework Statement Hello, I have a bunch of UV-Vis spectra to analyze and I am having a hard time choosing what the "onset" of each spectrum is, which I will use to calculate the optical band gap of each spectrum. Homework EquationsThe Attempt at a Solution I read somewhere that plotting...
  17. acvtre

    UV-Vis Amine Problem: Solutions & Explanations

    Good day to everybody, I immediately expose my problem. I'm doing some measurements with the UV-vis spectroscopy and I'm having problems with the amines in the non visible region. This is what I do: put my amine in a quartz cuvette -> do the background (reference) -> analyze the same solution...
  18. Chris Wallin

    A HF pulsed UV light effect on metal alloy

    I'm trying to understand the effect on a metal alloy of UV light (diode or laser) pulsing at about 1MHz. I am assuming that the stirring of atoms will generate heat, possibly moving the alloy to its eutectic point (depending on the alloy) and in particular to atomic motion. Can anyone...
  19. D

    Reflection and absorption of UV light

    Hi,I have a question when I was reading this website: http://www.webexhibits.org/causesofcolor/7F.html It explains how melanin works to protect us against UV light. From high school physics course we know that black absorbs light while white reflects. I understand when melanin accumulates,more...
  20. C

    Help with UV Light: Calculate Radiation Energy

    Hi everybody! I was hoping I could get some insight on how to calculate the energy of uva and uvb radiation at elevation levels of 0m in equatorial regions and at a lattitude of 35° N at 4500m in watts per square meter. Specifically, light in the range of 300-420nm. Any help would be...
  21. Sirsh

    Calculating Energy Requirements for UV Light Penetration?

    Hi all, I have a few questions in regards to UV light (or any other light on the spectrum) and if anyone could point me in the direction of any textbook or online resource to read up it would be appreciated. I would like to know how you can figure out the amount of energy required to produce...
  22. Garlic

    Is my handheld UV lamp safe to use for checking luminescent materials?

    Hello everyone, I own a handheld UV lamp, it looks like this: I've been using it for my hobby interests, like finding out what luminescent materials at home etc. Recently a friend of mine told me that germ killing uv light could be dangerous to sensitive retina parts. I know that this...
  23. Garlic

    Blocking violet light leakage in UV lights

    Hello, I have a handheld UV mercury vapor lamp, which, when working, leaks some visible light around violet wavelengths. My question is whether it is possible to block violet light but let the UV light using some kind of colored transparent sheets. Thank you..
  24. B

    How do I create a liquid that generates constant UV light ?

    HI Guys .. I really need some help on this ... I need to manufacture(mix) a liquid that 'displays' as UV light if that's the correct term. any ideas where I could start ? I have limited chemicals knowledge :/
  25. S

    UV Light Penetration: Explaining Heuristic of Photopolymers

    For a photopolymer, the heuristic goes that longer wavelengths of UV light penetrate deeper than shorter wavelengths of UV light. For example, the UVA spectrum penetrates more deeply into the photopolymer than the UVC spectrum. What is the best way for this to be explained?
  26. S

    How Do Longer UV Wavelengths Penetrate Deeper into Photopolymers?

    For a photopolymer, the heuristic goes that longer wavelengths of UV light penetrate deeper than shorter wavelengths of UV light. For example, the UVA spectrum penetrates more deeply into the photopolymer than the UVC spectrum. What is the best way for this to be explained?
  27. Jesse44

    Black Lights and plain CFL and Cancer?

    Hello, so I have just learned that CFL bulbs fall into the category of producing UV light, including perhaps some UVB in the case of black lights. I have had a black light bulb and a blue CFL running in my bedroom for almost two years now. I often fall asleep with the lights on, sometimes nude...
  28. M

    Formation of Excimer Structures: Explained for Engineers

    Reposting from another section... Can anyone explain to me how an excimer is formed? Like structure wise? Considering Xenon. I've gathered that an excited state Xe*, ground state Xe, and a 3rd body M react resulting in an Xe* excimer + M(carrying away excess energy). I'm struggling to find...
  29. S

    Forming new energy levels in semiconductor by UV light

    A new type of energy storage described which uses quantum way to store energy. ''Battenice''. http://techon.nikkeibp.co.jp/english/NEWS_EN/20140224/335902/ How exactly new energy levels could form under UV light? What do the mean?
  30. I

    Can UV Light Speed Up Fading of Car Paint?

    I recently repaired some damage on my car, which isn't quite done - I still have to scrape the runs. However, the paint is a significantly different shade from the rest of the car. I asked to have the codes matched, so I assume it's because of fading. Is it possible to mask off the old...
  31. D

    Why do welders use filters to block out UV light?

    When welder are working on pipelines, they use filters that block out UV light. Why is this precaution necessary? Does the question mean that they wear some type of glasses to help protect their eyes? or does the filter block UV light from going into the pipeline? This is what I...
  32. J

    UV Light and UV glue And Sunlight

    Simple question will UV glue that is supposed to be dried under a UV light dry or harden if taken and placed in direct sunlight? John
  33. R

    How do I test for UV light in colored LEDs?

    I recently purchased two strings of RGB LED lights, the kind you can set to all sorts of colors by combining red, green and blue in various amounts. Unfortunately, I strongly suspect that the blue and green led-pieces produce light that is contaminated with UV. Various UV-reactive things in...
  34. J

    Logarithmic Decay of Hypochlorite/Chlorine by UV light

    Hi, Does anyone know why the decay of hypochlorite/free chlorine in pool water due to UV light might show a logarithmic decay (natural log) as opposed to an exponential one? I did a chemistry experiment with scaled up concentrations of chlorine and cyanuric acid (scaled up 25x). Even in...
  35. K

    UV light absorption by transparent sheets – how?

    Ok thanks for the responses to my other question; I think I now have it. I have a follow up question – that is almost on the same topic (but not quite) The complete spectrum (arund 200nm to 380nm) of UV light is absorbed by some plastics?? Elections will be moved to a more energetic orbital...
  36. T

    Semen stains glows under black lights (uv light)?

    Hi all, Can anyone tell me if semen stains would definitely glow under a black light (UV light) ? I've been told that they would glow in greenish-yellow under the UV light. But later on someone said semen stains cannot glow without a substance called 'luminol'. Which one is true...
  37. R

    Does UV-C Light Provide Better Results for Curing Resins?

    Need a bit of help here and am not sure where to post this, feel free to move it to the right place if necessary. I have started to mess around with some uv curing resins for some other things I work on, however the current m.o. for curing them is leaving them out in the sun on a rotator to...
  38. S

    Which color reflect UV light best?

    Which color is the best reflector of UV light? In scientific-popular movie ``The future is wild`` they believe that high altitude gooses should have beauty blue color http://www.thefutureiswild.com/futurassic.asp?level1id=4&level2id=11&level3id=46&level4id=70" to protect themself from harmful...
  39. N

    How does UV light pass a glass bulb?

    Hi! A classic example in order to demonstrate the Photoelectric Effect, is to charge a metal plate (by electrons) connected to an electroscope and observe how the charge decreases when lightning by UV light. When put a pane of glass in front of the metal plate, we observe that the charge...
  40. F

    Understanding the Chemistry Behind Finding Blood with UV Light

    I believe many of us have seen this in CSI, or Dexter or some other TV show or something. Some guy spraying somekind of liquid onto a surface and pointing some UV light on it. The bloodspatter shows up, even though you could not see it without this method. So my question would be what's the...
  41. K

    Material that blocks visible light but not uv light

    is it possible to have a material block high wavelength waves but not low length waves? Gamma rays can pass through objects that visible light cannot. Any thoughts? I was thinking a certain bandgap?
  42. D

    Affordable Solar Cell for Sunblock Experiment | UV Light & Electricity

    I'm looking for a cheap solar cell for an experiment that we're doing on different sunblock lotions. Will a clear sunblock lotion (say spf 50) affect the ability for a common solar cell to produce electricity? If the answer to the first question is no, is there a solar cell that does use...
  43. N

    Absorbance of UV light by glass

    Hi, I'm doing an investigation into the absorbance of UV light by glass of varying thickness (constant density and standard type of glass) for an assigment. However, we're not actually supposed to carry out the investigation due to time constraints, so we're meant to make up the numbers...
  44. thenewmans

    Lyman-Alpha Blobs emit very specific UV light

    Himiko has been in the news and I’d like to be sure I have the context of this correct. They can tell the light is 12.9 billion years old by how much it’s red shifted. That’s roughly 800 million years after the big bang. In that time, the universe has expanded by a factor of 8. If the light...
  45. C

    Why Does UV Light Cause Sunburn But Visible Light Does Not?

    Homework Statement UV light causes sunburn, whereas visible light does not. Explain. Homework Equations N/A The Attempt at a Solution I'm guessing that it might have sinething to do with the electromagnetic spectrum.
  46. L

    Is There a UV Lamp that Can Generate 150 nm Light for Bandgap Measurement?

    Is there a UV lamp (not a synchrotron) that will generate UV light down to say 150 nm? I need a light source to do optical characterization (bandgap measurement as a function of temperature) of a wide bandgap semiconductor (~6.2 eV), so I would prefer a light source below 200 nm, ideally around...
  47. P

    Max Energy of UV Light Photon in Compton Collision

    What is the maximum energy a photon of UV light ( lamda= 320 nm) can transfer to an electron in a Compton collision? I used the Compton eq. and set cos= -1 and found the change in lamda to be 0.00486 nm. then using p=h/lamda where p is the momentum, i found the momentum for when lamda is 320...
  48. S

    UV Light Wavelengths Reaching Earth's Surface

    Does anyone know the range of the wavelengths of the UV light that reaches the Earth (ground)?