I dont use filters much and have no idea what you mean by 'flash'..
Do you mean lens flare?

With lens flare, and most lighting effects, you could make a new layer
(optionally)fill it with black
set it to screen blendmode
apply the effect.

Now you can move it around (but remember that if the effect extended outside the borders of your image, it will be cut off and that shows when you move it around)

DUAH, lens flare...  I'll give it a try THANKS.

+1
Photoshop lens flare filter can't be run on an empty layer that's why you need to create a layer with come solid color and blend it (you can use screen/black or overlay/50% grey).

UGHH, I tried it and it does not work. When I go to render, the lens flare is not an option...