How does UVB intensity vary with solar elevation above horizon?

Vitamin D is produced in exposed skin, proportionally to the intensity of UV-B radiation from the sun. The intensity of UVB varies smoothly, from a maximum when the sun is directly overhead, to a minimum when the sun is about to set. Given a normal, temperate zone ozone blanket, how does the UV-B intensity vary with angle from 0 degrees (overhead) to 90 degrees (about to set)?