"Daylight" bulbs covers a wide variety of bulbs, but all will have a colour temperature between 5000K and 6500K, bluer than a standard cool white which is 4000K or 4100K. They may be a fairly standard triphosphor bulb with a lot of blue or they may have a more advanced "full spectrum" formulation to provide much better colour rendition. The full spectrum bulbs tend to be quite a bit more expensive but not necessarily any better for plants. Treat them like a cool white, results may be somewhat better, but don't spend big money on a daylight bulb unless you check the spectrum to be sure it will be better for your plants.