There have been studies on the use of bright light therapy to improve sleep disturbances linked by combat-related post-traumatic stress disorder (PTSD).  Results are pointing to light therapy significantly improving sleep disturbances related to PTSD as well as moderate improvement in symptoms and depression associated with PTSD.
A lot of people who suffer from depression have problems with keeping a regular sleep cycle.  Those that use a light therapy box to regulate their sleep patterns, usually notice their symptoms for depression decrease.  Light therapy is an easy treatment that can be self-administered, and has few side effects.
There has been an ongoing study at the University of South Carolina that involves 16 soldiers who had been serving over seas.  The full article can be read from the following link: