Use the Animation>Keyframe assistant to convert your audio layer to keyframes. Use an expression to tie the keyframes to the value you are animating to create your strobing light effect. It could be as simple as duplicating your footage, setting the blend mode of the top layer to add and using an expression to tie the opacity of the layer to the audio keyframes.
If you are completely lost let us know and we'll try and point you in the right direction. This kind of thing is just a bit above AE 101.