Light intensity question

I sure hope this hasn't been covered in a previous post I've missed. I have a 44 gallon tall aquarium that I would like to convert to a planted aquarium and am trying to figure out the best way to fix up my lighting.

I have seen people mention that I should have at a minimum 1.5-2 watts of light per gallon or something like that. Don't various types of lights produce different levels of light per watt? Shouldn't I go by lumens or something? Is there an unspoken standard?

Thanks, I found some helpful posts. My problem arises from the fact that the longest side on my 44-tall is only ~21" which limits my lighting options.

I'm leaning towards a "Lights of America" model 9027 outdoor flood light which puts out 1863 lumens of 6500K light. It claims that it uses 27W and puts out as much light as a 150W incandescent.

If it ends up being too dim, I could always add a second. It's ~$30 initially and I think around $15-20 for a 10,000 hour replacement bulb. Has anyone here tried one of these?

(click here then on "specifications")