In alt.aquaria Nitesbane wrote:
What should one look for in a bulb then, if not color temperature? What
about using two different bulbs in combination? What is everyone's personal
favorite?

If you aren't growing plants in a freshwater tank, looking at color
temperature and CRI is just fine. In this case, you are likely trying to
accentuate the coloration of your fish, so using these metrics are a good
way to go.

If you're growing plants, my personal preference is to look at spectrum
first. Plants have very specific requirements when it comes to certain
wavelengths of light. As I already said, certain critical types of
chlorophyll need light in the 680-700nm range. The requirements of
photosynthesis in general is usually called the action spectrum. This has
peaks from 400-500nm (violet and blue) and 650-700nm (orange and red).
Many aquarium bulbs are good at providing the blue portion of the action
spectrum. It's the red portion that's a bit trickier to provide. So my
methods now are to have multi-bulb systems where the majority of the
wattage is provided by bulbs with decent red, and the remainder are a more
general aquarium bulb for balancing color. And if a bulb does not publish
its spectrum, it is not considered for anything other than the balancing
color bulb.