Originally Posted by
raybark
In incandescent lights, the color temperature is indicative of the spectrum. In both fluorescent and LED lamps, it is not. In fact, what is given is a "correlated-" or "corrected color temperature", meaning that it has been adjusted to simulate the appearance - to the human eye - of an incandescent lamp at that temperature. The human eye and the light-receptive chemicals in plants "receive" light totally differently, and are most sensitive to totally different parts of the spectrum. The eye picks up green the best, and that's where white LEDs emit the strongest, hence the apparent brightness, while plants are most sensitive to the red and blue parts of the spectrum.
If your T5 lamp is light a plant grow light, the phosphors have been selected to at least try to stimulate those chemicals, but if it is not - and to the best of my knowledge, nobody has matched those phosphors to white LEDs yet - it is designed for human consumption.
As to "warm" and "cool" or "cold" white LEDs, I used to have plant lights custom-made for me to resell, and my initial dismay was that the amount of red in them varies very little, so choosing one over the others was basically meaningless to the plants. I compensated for that specifically adding red chips to the boards.
From an energy efficiency standpoint, lumens per watt, "warmer white" chips tend to be better, so I would recommend going in that direction, but not to worry too much about it. Lumens is the key, and as Nicola stated, the more the better, as you can always increase the lamp-plant distance.