UV light can generally be subdivided into four parts: UVA (315–400 nm), UVB (280–315 nm), UVC (180–280 nm) and VUV (40nm to 200 nm).
When your skin is exposed to sunlight, it makes vitamin D from cholesterol. The sun’s ultraviolet B (UVB) rays hit cholesterol in the skin cells, providing the energy for vitamin D synthesis to occur. Flash is the most advanced VUV light therapy device on the market. There are no reports on the use of Flash to stimulate vitamin D production.