With shorter days and inclement weather, you tend to spend more of our time indoors in the winter. Unless, you are fortunate enough to be in warmer climates through the winter.
For those who are working indoors, artificial lighting and windowless rooms tend to add to the problem.
Full spectrum lighting can alleviate or at least reduce the problems associated with seasonal affect disorder.
According to recent research on vitamin D3, people living below a line running from Atlanta to Los Angeles, experience Vitamin D3 deficiencies because the strength of the sun is so reduced from October to May in these areas.
This same loss of sun exposure is relevant to seasonal affect disorder.
Full spectrum lighting would be effective in reducing this also, since it simulates the lighting of sunlight that enables our bodies to produce Vitamin D3.