I can't answer that directly. We have video recorded through a filter that was a standard welding dark lens in 7-9 shade.
Brad
I almost forgot. You should state what process, gas, voltage etc. as they all will influence the amount of lumens generated.
Brad
The average temperature of the welding arc is about 3,700 Kelvin (three thousands and seven hundreds, points and commas make a big mess among Americans and Europeans). The frequency of the waves generated is proportional to the fourth power of the absolute temperature. Does this help you in any manner?
Giovanni S. Crisi
Sao Paulo - Brazil
Wattage is easy, W=AxV
Don't know how this translates to lumens in an arc.