How effective are light boxes at combating sad? which light boxes would you recommend?

Light boxes are: a good option. You need to use ones that mimic full spectrum light which is like sunlight. Light bulbs that screw into household lamps are also available as an adjunct to this. As to brand and dose, you need to see a mental health professional who specializes in depression or light therapy. Also consider seeing a natural medicine professional. Supplements such as 5-HTP can be helpful. Peace.

Light therapy: Light Therapy can be incredibly effective for the treatment of seasonal affective disorder. You can buy low cost, small but effective light boxes now a day. I recommend use of white/ full spectrum light. The blue light boxes have been implicated in retinal damage and the development of age-related macular degeneration (AMD).