The screw in compact flourescent bulbs don't give off that much light unfortunately, otherwise I would use them now for my higher light needs.
60 watts of light may equate to 180 watts total but with restrike, dispersion and the lack of good effective reflector they will not require CO2 for the tank. I have a friend that uses 2 60 watts bulbs over a 10 gallon tank and grows plants well but doesn't need CO2.
I would say the equivelant light is only going to be about 25% so a 60 watt bulb is only going to give you a rating of 15 watts or basically the usage watts as Dave1 stated. Mess with it and see what it can grow, you may only need 2 of them or you may need all 4 to get the plants to grow. Screw in compacts are a new thing and there is a lot of information to still be gathered in their effectiveness and equivelant watts for aquarium uses.
Now a bank of these lights over a 55 gallon tank, say 6 of them with a good white background and an enclosed fixture might actually be enough light. It is just too hard to guess. Give it a shot and let us know how it works. I wish I could afford a water proof light guage to test the light levels but then I couldn't afford to feed the fish.
Laying them sideways and trying to make sure that the rods of the bulbs are parallel to the surface of the water may help some but again, it is all speculation.