Lighting questions: watts or lumens?

[KlcoKN]

Ok so I've been trying to do some research on what lights to get for my 55 gallon, I have a couple of low light plants right now and totally inadequate lighting even for them (2 24in 15watt fluorescents total).
I would like to get some medium light fast growing plants.
So I'm looking to upgrade... and I'm completely confused
Everyone says to use the watts per gallon rule, but I know that it breaks down when you are talking about really small or really large tanks, which doesn't apply to me, but it still got me thinking...
T5, T8, T12 bulbs all have different efficiencies, aka how many lumens they put out per watt used, right? Shouldn't it go by Lumens instead? And what about the light spectrum? I know plants need higher red and blue, but is that listed on the bulbs somewhere?

The wpg rule just seemed too simple, had to go and make it complicated and confusing for myself...

Also, looking at shop lights at wal-mart I noticed the package said not damp rated... getting damp or wet rated lighting fixtures sounds like a good idea for something sitting only a couple of inches above water, right? but I can't seem to find any shop lights even damp rated, any suggestions?
Or any of you know of a decent aquarium light for really cheap?

 

[Slade]

I'm no expert, but the higher the temperature (degrees K) the more blue spectrum. Daylight is about 6500K and probably the best full spectrum you'll find for T815W. The bulbs sold as aquarium/plant are around 2600K and have a pink glow, I don't understand how these are better for aquarium plants. You're better off with T5HO or LED.