different kelvin ratings on bulbs come with different expectations
6500K is not specific to growing plants, it's the expectations that plants will benefit from it the most
it is this expectation that drives marketing to say they are grow bulbs
after 6500K for growing plants you are looking at bulbs specific to growing ... these no longer have a kelvin color rating because it no longer applies
after that, ... well that's a whole different area of study, then you get purple lights that are dim to us, and expected to be very bright to plants
i like the T5 flourescent size, ...
basic T5's are the most bang for your watt.
T5VHO (very high output) has the most output, ... and the most input, but the same size
T5HO (high output) seems to be a common standard, ... enough light output without being excessive power input.
regardless of what you do, it's size that is going to limit or dictate how much light you can put in your tank
a spiral compact fluorescent has a very small tight space
a linear bulb is thin & long
a metal halid is also compact
induction lights, ... not so compact,
LED, spread out (unless you make your own)
each of these will change what is possible.
what light intensity do you want ?
LED is almost impossible to get 7 watts per gallon (marginally more efficient than fluorescent)
fluorescent, you can get 7 watts per gallon easily enough
metal halide you could get ... 2000watts over your tank
sunlight will give you more intense light than LED or fluorescent (may change due to weather, but a sunny day you have some very intense light)