Lighting?

Why do people normally recommend a 600w light over a 1000w? Is there something I'm missing?

600W are reputed to give more lumens per watt.

Well shit that is what I was afraid of.

1000W will still give you a lot more lumens - just slightly less efficient.

A 1000 watt light doesn't cover much more area than a 600 watt light, and is less efficient as far as how much light it puts out compared to how much electricity it uses. Because the 1000 watt lights get so hot they must be kept further away from the top of the plants which means you're wasting more light since every inch really counts as far as light loss. It usually would make more sense to get two 400 watt lights as opposed to one 1000 watt light. The two lights will use less electricity total, be more efficient, be able to cover a wider area, and can be kept closer to the plants so you're wasting less light.