That’s a good question. Now that the Power settings is measured in Watts, I’m not sure of a clear conversion from the old style lights.
I always go by sight / feel personally rather than measurement. The way I like to “measure” light power visually is by using a neutral gray material (0.5 diffuse color with no specular) on the subject model, like in the screenshot. If the lighting makes the subject’s grey look correct and not too dark or too bright then I can generally trust that the light power is appropriate.
