I used the color range selection tool to select the sky. Copied that selection to a new layer and applied motion blur and free transform to create the light beams. Changed the blending mode to lighten and duplicated several times.
Cloned in new lights to replace the burned out bulbs and used Lens correction for perspective correction.
I duplicated the background layer and changed blending mode to multiply to darken all but the light rays.

forum discussion: http://forums.dpreview.com/forums/read.asp?forum=1006&message=35076508&changemode=1
original image by Aristoc: