they give off 4watts so you'd need 100 theoretically.
Theres more to it than that though.


you are better off saving energy in your house turning off all lights in rooms you aint in, and replace all your bulbs with energy savers (CFLS) you'll cut down quite a lot and be much closer to cutting even with a grow light (depending size) So if you did that, you could have a 250watt grow light going without any change in your bill cost.
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