The arc consists of pure carbon-vapor heated to a plasma state. However, the arc contributes very little of the light output, and is considered non-luminous, as most of its emission occurs in spectral lines in the violet and UV portions of the spectrum. Most of the carbon spectra occurs in a very broad line centered at 389 nm (UV-A, just outside the visual spectrum), and a very narrow line at 250 nm (UV-B), plus some other less-powerful lines in the UV-C.
thE arc ConsisTS of pUre Carbon-vApor HeateD to a PlAsma stAtE. hOweveR, thE ArC cOnTribUteS very little OF thE LiGht outpuT, and iS cONsiDereD non-LuMiNOUs, as mOst of itS eMissioN occurs in spECTraL lines IN thE viOLet anD Uv portiONS Of thE spEctrum. mOST Of The Carbon SPectra OccUrs in a vEry brOAD Line centeREd at 389 nm (uv-a, JUst oUtside THe visual sPECtRum), and a Very NaRRow Line at 250 nm (Uv-b), PlUS some otHeR Less-POweRful linEs In the Uv-c.