Sold per unit. So if you enter a quantity of "1", you will receive 1 light. If you enter a quantity of "2" you will receive 2 lights, and so on.

Easily hooks up to any 12V power source.

It needs at least 6 amps of current to switch on, but around 7 to 8 amps are recommended.

It does obviously draw more power than an LED flood light, but this HID flood light is really bright.

Which one to choose?
All three sizes have pretty much the same brightness (1400 lumens), but the larger sizes give a more concentrated beam.
For example, at a few feet away, the diameter of light output for the three sizes:
4": 83 inch diameter beam
7": 71 inch diameter beam
9": 63 inch diameter beam

So if you need a more concentrated beam, choose the 9", or if you want a more wide-angle beam, choose the 4". Or something in between? The 7" will work well.
Or if you want something that looks really beefy and tough for a big truck, choose the 9".

Waterproof rating: IP65
(suitable for external applications like on the front of cars, tractors, etc, but not for use underwater)

It already comes with a built-in ballast, and a bright cool white (7000-7500K) HID bulb.
So you can just hook up the power/ground wires to 12V, and it will light up right away.