It was my understanding that glass as a material blocks UV.
Quote from a Google search - There are 3 types of ultraviolet radiation, but only two reach the earth's surface. These are UVA and UVB. UVC is filtered out by the ozone layer. UVA mostly causes skin ageing and research has now shown that it is also likely to cause skin cancer. UVB causes redness and sunburn and is a major risk factor for all types of skin cancer. Most glass used for windows blocks UVB but not UVA. This means that although glass might reduce the risk of sunburn, it does not prevent long term damage from UVA.
Guess it does not block as much as I thought. Pat