No, the k rating has nothing to do with intensity or anything. It's the color of the light. Plants in an aquarium can only use light in the 6500k-10,000k spectrum. You shouldn't see a price difference in any bulbs of the same length and wattage in that spectrum. Bulbs come in all color temperatures, some reef tanks use bulbs in the 20,000k range. It's kind of complicated, but the easiest way to think of it is like a prism. You get several different colors when you shine light through one. Plants can only use one of those colors, and the kelvin rating says that color is in the 6500k-10,000k range. If you take the next color, it may be in the 12000k-18,000k range, etc. make more sense now?
So... the K rating does not measure how strong the lighting is? In other words, 6500K is not lower lighting than 8500k?
As far as getting plants that require more than 'low light', you'll have to increase the wattage of the bulbs. That will require a new fixture. Aquarium fixtures have several different kinds of bulbs. In a typical fluorescent setup, you have T-8 (which is what you have), T-12, VHO (T-12 on steroids), T-5, and T5HO (T-5 on steroids). The 'T' is the diameter of the bulb in 1/8", so a T-8 is 1" in diameter. You also have compact fluorescent which is typically a bulb bent to a 'u' shape, and Metal halide, which is what a lot of high end reef tanks require.
Did that help, or confuse you more?
Haha, uhhh I am sort of confused right now... so if the wattage determines whether the lighting is low-light or medium-light, than I don't understand the point of a K rating. Are you saying that some low-light plants require different K rating than others??? I thought a plant was either low-light, medium-light, or high-light. So say plant A needs low-light, with a certain wattage, and plant B needs medium-light, with a certain wattage. Where does the K rating come into play? Can plant C, which like plant A requires low-light, have a different K requirement?
