Lighting for plants

To all the aquarium owners,

        I currently have a 30 inch aquarium, and I am about to start a new
aquarium. The three light bulbs that I am currently using are brands called
Triton that is about 15 watts each. Plants in my current aquarium aren't
growing well. 

Since I am starting a new aquarium that is 40 inches, can someone please
give me some advice about what lightings are best suited for plants in general?

Thanks for the help!
Ronald Tsang :)