an electrical question

Let’s say I have a light fixture in my bathroom that has three lightbulbs in it. Do the bulbs have to match wattage to get the maximum life out of the bulbs, or does it not matter?

i.e., if I have a 60w-60w-60w configuration, would that last longer than
a 75w-60w-60w configuration? Does the mismatched wattage cause an irregular draw on current that would make one of the bulbs in the mismatched string burn out more quickly?

It really doesn’t matter. Light fixtures like that wire the lights in parallel, it’s as if each light is on it’s on circuit. Just don’t exceed the total recommended wattage for the fixture, this can cause overheating and other nasty problems.

If you’re losing some bulbs more than others in your bathroom it’s probably because some are getting more moisture than the others. I have that problem with mine, the lamps on one end burn out more frequently than the others.

How does moisture on the outside of a sealed bulb cause the filament on the inside to burn out faster?

It doesn’t have to. Firstly, I assume CFLs since that’s what I see most often nowadays. I don’t know why moisture affects them more but it does. Secondly, if you’re going through a lot of bulbs in one fixture you can often find some clues on the old bulbs or by looking at the fixture itself. The base of the lamp will often show some signs that it’s been arcing a bit, possibly because it won’t screw into the socket fully, moisture between the base and the brass tab in the socket.