So, when I take a shower, most of the time it is during the daytime. I leave the lights off because I see no reason to have the lights on when the room is plenty lit.

I have 4 vanity lights, and I want to know how much electricity I would be saving on average if I take a 10 minute shower with the lights off.

Try emailing MythBusters at Discovery.com, they did a segment on power consumtion of light to see if it was better to leave the lights on when you are just gonna leave the room for a minute and come right back. They proved it was better to turn them off because the power consumtion when you turn them on was negligible.

just find out how many watts they are rated at, and you can calculate it

post the bulb info

I'm pretty sure they are just regular 60W bulbs.

if its a 60 watt bulb then:
4bulbs * 60 watt per bulb * 1/6 hours *1/1000 = kilowatt-hours per day
my calculator says you save about .04 kilowatts perday. i pay about 20 cents per kilowatt

the variable they ignored is the fact that turning a bulb on and off causes it to burn out quicker. no idea if this happens to florescents as well.

No, the test had nothing to do with how quick the buld burns out, it had to do with power consumsion of the various bulbs. So that variable isn't considerd in the tests

Maybe this case doesn't apply for the shower, but when light bulbs are off, you don't save power because it will need more power to actual warm the room. (during winter)

If you're going to take longer then 15-30 minutes, then turn them off. Otherwise, it won't make much of a difference.