What is the precursor of vitamin d made in response to uv light?

the precursor of vitamin d made in response to uv light is cholecalciferol. It was converted from 7-dehydrocholesterol by using UV light. 
Sunlight is a vital component in vitamin D because the skin needs it to make vitamin D. Vitamin D is helping calcium absorption, thus helping to keep teeth and bone. Vitamin D is also available from diet source.