# Why does welding produce UV light?

Looking directly at a welder is dangerous because large amounts of UV light is produced. What makes this light? Is it electrons from the current that excites metal atoms, and these atoms sends out UV light? Or does the extreme heat have anything to do with this?

Is it dangerous to look directly at a nail being melted (glowing brightly) by hundreds of amperes?

Is it dangerous looking at an oxyhydrogen explosion in itself, or could it be dangerous if the explosion touches other substances exerting UV light because of the extreme heat of the explosion?

• I know of (at least) one method of welding, which produces no UV light. So your question is wrong primarily. – Georg Mar 3 '14 at 21:43
• @Georg I didn't know! Which method is that, and how does it differ from the others? – Friend of Kim Mar 3 '14 at 22:49
• Dropping a nail across a source with source impedance that low sounds kind of dangerous on many fronts unless you really know what you are doing. If you're planning on doing this for a lark with a car battery, DON'T. – WetSavannaAnimal Oct 22 '14 at 12:12

All materials emit thermal radiation (such as light). The hotter the material, the more the radiation is shifted to high frequencies (shorter wavelengths). The radiation comes from oscillating electrons (regardless of whether there is an electric current). Welding reaches temperatures high enough to cause significant emission of UV light. Oxyacetylene and oxyhydrogen flames can both be over 3000 C degrees and therefore can produce hazardous amounts of UV light. Arc welding is even hotter and produces more UV light. Running hundreds of amps of current through a nail would be similar to arc welding.

• light from welding is quite different from light emitted from hot materials. the spectrum from hot materials is smooth. yes it shifts to UV range when materials get hotter. however, plasma's spectrum is very different, it can be chopped in lines and bands – Aksakal Mar 3 '14 at 2:44
• Thank you for a good answer. @Aksakal Are you saying welding emits more UV light because of a special case? What is this? I'm making an oxyhydrogen generator. Could it actually emit UV light damaging my eye sight? Since UV light is outside the visible spectrum, it would do harm without anyone knowing. – Friend of Kim Mar 3 '14 at 11:33
• Yes welding is a special case. What kind of generator you are making? – Aksakal Mar 3 '14 at 12:12
• @Aksakal I'm doing this mainly to fuel a spud cannon. And because an oxyhydrogen explosion is so powerful, I'm not going to need too much of it. I was planning to make a simple electrolysis generator with some stainless steel electrodes. However after discovering the dry cell, I'm considering that as well. Anyway it is going to produce roughly 5 liters per minute at 100A for quick reload time. This is why I'm worried if the explosion could damage the eye sight. – Friend of Kim Mar 3 '14 at 12:46

in welding a plasma is created, it's a mix of ions, electrons and atoms. alltogether they are a neutral mix. once you get plasma you get a ton of UV coming out of it, very dangerous to eyes not only on the direct contact, but also via reflection from other objects.

in your case, I still don't know what exactly is the device you are creating. It sounds like there's a similar condition to welding with a lot of current going through air. that's what creates plasma in welding. can you point to a description of a similar device on web?

don't go to the court with this :) but I doubt that there's significant UV during what appears like explosion. I don't think it's plasma, there's probably some ionization, some UV, but not much at all. now, i'm going to run and hide from your lawyers :)

• Good answer. I'm making an oxyhydrogen generator. It just separates $H_2O$ into $2H_2$ and $O_2$. When these two gases are ignited, they explode. The temperature is between 2300K and 7000K. It all depends on how fast the explosion happens. Could this emit dangerous amounts of UV light? – Friend of Kim Mar 3 '14 at 13:05
• $2H_2 + O_2 \to 2H_2O + \text{energy}$ – Friend of Kim Mar 3 '14 at 13:12
• yes, but I have to think a bit, whether you're dealing with detonation or deflagration. the mix of hydrogen and oxygen is called knallgas in German, not sure what's it in English. – Aksakal Mar 3 '14 at 13:17
• for instance, this guy is trying to explode knallgas, but it looks to me like deflagration, not even the detonation, and certainly not an explosion (chemistry-chemists.com/Video/hydrogen-explosion.html#1003) – Aksakal Mar 3 '14 at 13:26
• @FriendofKim If the temperature is 2300K to 7000K there will be dangerous amounts of UV light. – DavePhD Mar 3 '14 at 14:52