Color temp is purely a number made up for consumers. It is not scientifically useable.

Quote Originally Posted by dataman19
T5s are almost true white lights as well....
Nope, they're pretty far off from "true white" if what you mean is sunlight. If you buy a cheap spectroscope and look at your light source, you will see it's very different from sunlight. You can get one for $20 and I used it to get some idea about my light sources. This is an example picture of what it shows you:



AND HERE IS HOW COLOR TEMPS WORK, YOU CAN ONLY GO ONE WAY WITH THE NUMBER (CALCULATE IT) BUT ONCE YOU HAVE THE NUMBER IS IS NOT VERY MEANINGFUL AND TELLS NOTHING OF THE LIGHT'S QUALITY FOR PLANTS: