Mercury Vapor.

How well do Mercury Vapor H.I.D lights work for growing? Im asking cause they are cheaper then HPS and MH Lights.

Not worth buying, they suck.
Too hot and the wrong spectrum

Oh yah, From what they say they have alot of blue spectrum.

Mercury vapor is the type of lights that were used for streetlights many years ago. Not very good for growing because it doesn't provide enough of the right kind of light spectrum. While they do provide a little of the blue spectrum, MV also produces too much heat to get very close to a plant, and are very inefficient to operate.