what size light for a 3x3 tent?

Led,s are very popular with growers are they comparable to a hid light.
I've always seen led lights as something you would use when space/height is an issue, how do they compare?

HID lighting produces great product. That has been proven. Led similarly produces great product and some would argue has a better spectrum. Cmh is also out there and growers are having great results. IMO led's biggest advantages are efficiency and lot less heat.