It has been presented results of measurements of UV and IR radiation and the radiance of visible light during welding of X5CrNi18-10 chromium-nickel austenitic steel and X6Cr17 chromium ferritic steel by CMT and ColdArc methods as well as during braze welding of DX 54D and DP600X steels covered with protective layer of pure zinc or zinc-iron alloy. It has been shown that the optical radiation intensity increases together with the increase of welding current and arc voltage. Moreover, the radiation intensity is affected by welding/braze welding methods and the kind of shielding gases whereas the influence of parent materials kind is difficult to assess.