First off, before animating it, you'll need to create the effect. For this demonstration I've used a white/transparent Reflected Gradient on a new layer. Now open up your animation window by going to Window > Animation. To add a frame, click the button at the bottom of the animation window next to the trash can. Essentially what you're going to need to do is create about 15 frames, and in each frame move the layer with your lighting/flash effect a little bit to the right.

Not my best explanation but it's going on 2 AM, hopefully it's understandable. I've uploaded a sample I created to help demonstrate the process.

And the final product:

It's perfect! Thanks for the help, I certainly do appreciate it.

well, that's really a good method~