Here's a tool you could use to figure it out. First find the lumen output of HPS or whatever you want and reverse the calculator to give you an equivalent wattage of incandescent. Makes for interesting (surprising) results sometimes.
The big problem of this calculator is, it does not respect how the efficacy varies with power level of the light source. Plus many figures are rather outdated or generally wrong (mainly fluorescent). So you have to fill in more reasonable efficacy figure directly.
And there is one other argument against such simple compare: Many light sources are far incompatible with the light color quality and light source geometry. The first is important when there are some difficult conditions, where the specific color property improves the visibiluty far beyond the illumination level, the geometry then limits the attainable efficiency of the fixture optical system, so light lossesinmany applications. So e.g. indoors the fluorescent will giveway better visibility than HPS of the same lumen output because of less shadow/glare problems, but in a road light the HPS would be far superior due to large amount of spill light from the large fluorescent.
