There has been much research on vitamin D in recent years, and this research shows that vitamin D is not only essential for calcium metabolism and bone health, but also for a number of other functions in the body.
Low levels of vitamin D are associated with impaired musculoskeletal function, cardiovascular diseases, diabetes, cancer, autoimmune diseases, depression and multiple sclerosis. Based on new research says most researchers in the field that the recommendations for vitamin D should be increased from current levels to 20-25 micrograms per day.
Bright light in the visible spectrum (without any vitamin D producing UVB) clearly improves mood, although it is hard to conduct good studies due to the lack of a control condition.
The NIH recommendations http://ods.od.nih.gov/factsheets/vitamind.asp are much more conservative than "The Vitamin D Council" which seems to exist of one gadfly doctor (psychiatrist) and 4 unnamed others. This doesn't mean he's wrong; he certainly has the links to back up his assertions.
NIH notes that sunlight and diet is unlikely to cause toxicity and it is "much more likely to occur from high intakes of vitamin D in supplements. The Food and Nutrition Board of the Institute of Medicine has set the tolerable upper intake level (UL) for vitamin D at 25 μg (1,000 IU) for infants up to 12 months of age and 50 μg (2,000 IU) for children, adults, pregnant, and lactating women [4]. Long term intakes above the UL increase the risk of adverse health effects."