Hi,
As far as green plants are concerned, they love intensity but they only respond to certain wavelengths (or colours). They thrive on red/orange and blue/violet light but they reflect green light (hence the plant appear green to us).
Since it is much cheaper for us to buy high intensity red/orange (aka low kelvin lights) lights than it is to buy high intensity purple (aka high K), I believe low kelvin lights are the best solution.
Broad spectrum daylight isn't bad for plants, its just not ideal. Its light is balance. It may not have a strong red/orange or a purple component. Since high and low kelvin lamps may have a stronger component in those regions, these lights will do better than daylight.
Its all IMHO of course
- Victor.