You want UVB and not UVA, but UVB is weaker than UVA so all sunblocking type products necessarily enrich your exposure to the bad kind. The time when the ratio

You want UVB and not UVA, but UVB is weaker than UVA so all sunblocking type products necessarily enrich your exposure to the bad kind. The time when the ratio of UVB to UVA is highest (best time) between 10 am to 2 pm, or when your shadow is not longer than your height. So 20 mins in the sun at noon without sunblock is best, and after that if you’re pale then slather on the sunscreen.