I can't believe I'm struggling so hard with this. I'm building props that need about 10 light bulbs. These need to be battery operated units. The bulbs want to be about 2" diameter clear. These will need to run for about 40 minutes on a charge. So I'm looking at 12v, figuring that's the easiest to get batteries for. I'm figuring about 15w max to be able to run on a reasonably sized/priced battery (as is I'll need 18-20 Ah which is a high-end motorcycle battery). Trouble is, I can't find any 12v 15w clear bulbs in the 2" range. Any suggestions on a source? Or another way to look at it? If I get a 24v 25w bulb and run it on 12v, will it be similar to 12v 15w? Also, does wattage more-or-less equal brightness, regardless of voltage?