xpLight works in conjunction with a Sprite object which is generating lights.

General tab

xpLight General tab menu.

Enabled

Checking this box activates xpLight.

Mode

Set at Independent, by default.

You can change this to Action-Controlled.

Independent Mode

In this mode, particles will be affected if they come into the field of effect of the modifier.

Action-Controlled Mode

When in the Action-Controlled Mode setting, the modifier will only act on a particle when told to do so by an action.

Spline Timing

Set as Particle Age, by default, all the parameters which can be changed with this modifier are controlled by splines.

How the splines are used depends on this setting

The alternative option is Step Count.