UVB bulbs set off a chemical reaction that produces a "fluoresce." this chemical reaction is caused by ionizing radiation (ionizing = creating atoms that have unequal amounts of electrons to protons. radiation = energy that travels through a substance to be absorbed by another substance) so basically, UVB bulbs emit radiation to disrupt atoms and make them "ions" whih causes a chemical reaction to produce Vitamin D3 and UV rays. thats what i heard, so it might not be that accurate