you could also just create a new layer (CTRL+SHIFT+N) then FILTER>>RENDER>>CLOUDS then FILTER>>RENDER>>DIFFERENCE CLOUDS and then invert the colors (CTRL+i) and then change the levels (CTRL+L) and slide the grey triangle all the way to the right. That should work a bit better.
not very effective in my opinions try making fidderent, lightning with black background, filter render clouds, filter render different clouds, blending mode screen, colour balance.