Paint With Light Photoshop action
by Chip Springer.
Available at http://www.atncentral.com/download.htm
For a complete tutorial and discussion follow this link to dpreview: http://forums.dpreview.com/forums/read.asp?forum=1006&message=11650687.

For those who do not have Adobe Photoshop or have an image editor that does not support
Photoshop actions, such as Elements, you can make your own PWL layers. Here's how:

For the Paint Light Layer:
1) Layer > New Layer. In the dialog box that pops up:
2) Rename to Paint Light if you want.
3) Mode > Color Dodge.
4) Check the box = Fill with Color Dodge neutral color (black).
5) Hit OK.

For the Paint Shadows Layer:
1) Layer > New Layer. In the dialog box that pops up:
2) Rename to Paint Shadows if you want.
3) Mode > Color Burn.
4) Check the box = Fill with Color Burn neutral color (white).
5) Hit OK.

Now you can proceed to paint in shadows and light just as you would using the action.