Why LED? The technology is finally where it needs to be to produce large yields and save you big money on electricity, HVAC, and upkeep. Remember how much heat HPS lights produce and how you needed to change your bulbs every crop or two? Remember the giant 50lb air-cooled reflectors? Pepperidge farms remembers.. We're trying to forget!
What Kind? You’ll see there’s two primary types of LED’s below. Board style and bar style. The difference is one is built on a quantum board (it’s smaller in size and uses higher wattage diodes) and the other is built with bars that have a lot more diodes with less wattage per diode. It comes down to preference, ceiling height, and growing style. You'll lean towards a bar style led grow light for sea-of-green and screen-of-green style growing and a board style if you're growing big/tall monsters. The board style lights usually penetrate deeper but don't cast as wide of a footprint. See manufacturers recommendation on mounting heights but generally board lights should be 28-36+ inches away from your canopy, and bar style lights can be as close as 6-12".
Spectrum: Going with a full spectrum LED Light will allow you to use the same light for vegetative growth through flowering and up until harvest. If you have two rooms, and a dedicated light for each, you can definitely see some benefits to a veg spectrum with the addition of more blue wavelength LED's helps prevent over-stretching, stimulate stronger root growth, tighter internodal spacing, and larger leaf size while in the vegetative stage of growth.
