theoretically yes... supposing that the smaller and bigger light sources are of equal efficiency and have the same spectrum. The number of photons emitted adds up linearly after all (I think it even works if the spectra are different.)

In practice, as it turns out (... "let's read lots of wikipedia about lighting" project), a 100W bulb produces roughly 1.5 times more lumens per watt than a 40W one, so the "equivalence" is also somewhat questionable... as it's the lumens that count (that being "the perceived lightness that is radiated").

(This thing is called "luminous efficacy", by the way. Am I the only one who thinks that it would make a nice LW post title at first look?)