The light that is required to increase vitamin D production is UVB. The Penn State researchers used a pulsed UVB source for their research. Lower frequency ligh

The light that is required to increase vitamin D production is UVB. The Penn State researchers used a pulsed UVB source for their research. Lower frequency light will not activate the conversion to vitamin D. Glass absorbs most UVB light therefore laying out mushrooms on a window sill will not work.