According to some clinical data, most of vitiligo patient had history of be under sun for quite long time before having vitiligo,or illness deteriorate. That is because sunshine in summer have high exposure rate, and it will be easier to cause inflammation after skin exposure for quite long time, which lead to melanophore damaged and lost their power to product melanin, result of that is skin decolorized. Thus a lot of vitiligo patient is afraid of expose them self under sunshine, and worried about summer coming.
As we all know, the ultraviolet ray in sunlight will deepening color on skin, and UV light can active the specifical enzyme ( Tyrosinase ) which used to product melanin, and accelerate tyrosinase transfer to dopamine etc, in that case advance the metabolism of melanophore. So get some sunshine form time to time could help generate melanophore, and speed up melanin transfer from melanophore to skin surface, and deepening skin color, thus assist vitiligo treatment. But on the other hands, UV light will hold up substance what will become sulfydryl which in skin environment, the later one can control the active of tyrosinase, which is adverse to metabolism of melanophore.
So vitiligo patient should try to avoid long time exposure under sun, but it can advance metabolism of melanophore if take into consideration the circumstances, balanced amount of long wave UV light without skin damaged. In another word, vitiligo patient should take some sun light actively. But it should adjust as season changed, like it should choice after or before noon in autumn, winter and spring, it can take a little bit longer than usual. In end of summer and spring, choice morning and dusk will be best choice, if you only got time at high noon, you should get sun light through window, and time should be less, but it can take a few more times during this period. It will be helpful for vitiligo treatment.