Indirect lights require a small transformer. This type of light works better in the darkness because it can run on a very low voltage, but a high current. This is much more durable than a direct light source and they are fairly inexpensive to buy. The benefit of using this type of light is that there is no risk of damaging the wires or causing the lights to come off of the motorcycle.
The best way to determine which kind of auxiliary light to purchase is to examine the motorcycle itself. If you see that the light will be running directly from the battery, then it is a good idea to purchase a direct light. If there are not many wires attached to the battery box, then you may consider purchasing an indirect light instead.