What are the contraindications for light therapy treatments?

If you are referring to the light therapy used as a (questionable) treatment for Seasonal Affective Disorder (severe winter depressions), the most apparant contraindications deal with potential ocular (eye) damage.

The full-spectrum devices have frequencies at both the red (infrared) and the blue (ultraviolet) ends of the spectrum that can cause various eye problems. Also, especially with the "blue enhanced" devices, overexposure to ultraviolet rays could cause skin problems including the possibility of skin cancer in severe cases.

Since people with this ailment (SAD) are likely to be Vitamin D deficient, you might be better off to take cod liver oil or halibut liver oil supplements through the winter months, and perhaps also calcium supplements, and then find something to do to keep from sleeping all winter.