Thanks to Wikipedia: Ballasts are used where an electrical load cannot effectively regulate its current use. These are most often used when an electrical circuit or device presents a negative (differential) resistance to the supply. If such a device were connected to a constant-voltage power supply, it would draw an increasing amount of current until it was destroyed or caused the power supply to fail. To prevent this, a ballast provides a positive resistance or reactance that limits the ultimate current to an appropriate level. The combination of a negative-resistance characteristic and a series impedance allows a stable operating point to be maintained. Examples of such negative-resistance devices are gas-discharge lamps.
Are you using an HID light? If so does your reflector have a built in ballast? Can you link me/us to the products you're using?
you need the proper ballast, for the lamp... never mismatch: wires, bulbs, fuses, motors, ballasts, or any electronic device. working with electricity requires some caution. i am not an electrician, but i have learned the hard way to match everything properly. fires, burns, and electrocution, are the outcome of not matching properly.