What size aquarium light should ..

Brief：
I read that a good rule of thumb is watts for every gallon? I have a 29gallon aquarium, so 29-58 watts of light? I find that a huge difference. I also.. 

I read that a good rule of thumb is watts for every gallon? I have a 29gallon aquarium, so 29-58 watts of light? I find that a huge difference. I also find it especially difficult to find a light with this wattage to be the correct size for my tank. It seems the higher the wattage, the longer the light. But if I go any smaller in size, the wattage is reduced. I also read that 2 fluorescent lights may be used, but my hood will only house one light. My plants require low-medium light, and low-medium growth rate, ph of 6.0-8.0, so they're generally easy plants to look after. I am experienced keeping Angels, but I can't seem to keep a plant alive! I am trying! There are HUGE benefits with plants and my Angels are happier. Every article I read about lighting for plants contradicts another article I read. One article says that the K rating means nothing, and another article's author swears by using 5000-10000K lights. WHAT do I get? Help!

I've grown plants for years and currently own a 29 gallon low tech planted tank with plants considered hard like cambomba growing well. Pretty much lighting wise, the K spectrum does not matter. I've grown plants under cool white bulbs (though these make the fish look bleached out so I don't reccommend it) to more specialize "planted tank bulbs". The plants don't care. My substrate is plain old gravel and I use the Estimative Index for fertilization. I've done everything from pressurized CO2 to natural lighting only but currently prefer the the non CO2 low light method since it involves a lot less pruning.