ONe way is to create a conventional lens flare effect on a much larger comp, render that movie, import, then place the movie in your action comp, adjust the blending functions to get the overlya you're hoping for.
ArtBeats (and other movie clipart sources) has lots of lens flare and color wash effects, including film flash frames and edge fogs, that you can preview on their site and then deconstruct.
there are many other ways to simulate errant light sources. If you have a basic understanding of lens optics and what causes flares, you can simulate these artifacts with some thought. It helps to know how to use blending and composite mode settings.
First created shape layer that is Close to the base color you want for your flair. Second add fast blur or Gaussian blur of a value that is about half the size of your shape layer. Change the blend mode to add, duplicate, increase the blurb about 50%, duplicate repeat until you get what you want. Many times when creating this kind of an artificial lens flare effect I would use many different colors in the same flare. Sometimes I will make the layers 3-D and move them around in 3-D space.
The only other really good option is to buy some stock footage of real lens flares and colorize them using color grading effects.
by the way, one color grading and creating "light" affects you should always work with 32-bit projects.