Make a brush to create simulated holiday lighting.
I started with a custom shape (upper left),but a free hand drawing would work fine.
Create a brush from this picture, then change the brush settings for spacing,
color jitter, angle jitter. Play with all the other settings to see what they do.

Paint the "strings of lights" on a new layer. I used the linear dodge layer blending
mode for the brightest effect and duplicated the layer for greater brightness.
Then I added an outer glow layer style to one of the layers. (Gaussian Blur works also)

forum link http://forums.dpreview.com/forums/read.asp?forum=1006&message=21040596