I'd be interested in what others have to say. I upped my 3500K bulbs to 6500k and kept the same wattage and it made a big positive difference in my plants. But maybe it would have been just as good to keep the same "k" rating and raise the watts???
The Kelvin rating for bulbs has to do with what color range the light is in. Unlike wattage, more (or less) is not necessarily better - it depends on your personal situation.
As I said - I have a fixture with a 6700K bulb and a 10000K bulb. One is good for plants, one makes the tank look better.
Pick a bulb and wattage based on what type of plants and fish you intend to keep.
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