Light effects: Need help!

[Raeiphon]

The most i've done with light effects is the flickering of lanterns and a really basic fading shield. I'm not a whiz at mathematics/operations by any means and I have no idea where to start.

Basically, what I want with this effect is for lights to hover around the player and dance, like fairies of such. I cant, however, think of any mathematical operation that'd loop to a certain value then jump into the minuses so my knowledge can transpose that into a backwards movement.

A lot of help here would be brilliant. I learn best off snippets.