Refer to the Wave Effect tutorial for more precise intstructions
open your document, make a new document of the same size. Select paint bucket fill tool, make it white, and fill the background. Select paintbrush tool, make it black, with hardness of zero, size of about 56 and just draw some lines across it.
Paste it as a new channel in your other image, go to lighting effects, select that as your channel, and do all the other settings. Heres what it looks like
:P n1