A common misconception is that a SAD light box works by raising your vitamin D level. This is not the case. A light box blocks out UV light like a good pair of sunglasses. Vitamin D levels increase with skin exposure to UV light. A SAD light works by exposing the eyes to non-UV light of sufficient intensity to cause a decrease in melatonin and an increase in serotonin.
Maintaining vitamin D levels can elevate mood but a SAD light will not serve this purpose.