400w Metal Halide for first month of flowering?

[Earthy Dank]

What is a rail? how do they work? and how much do they cost?

Its a rail... with a motor that moves the light very slowly so you light covers a larger area. And since the light moves you can keep it much lower to the canopy without burning it. And they cost around 50-200 dollars depending on where you look and what kind.