A 2mm acrylic sheet has a fairly sharp cutoff between 375 and 400nm, so transmits about 17% of all UVA (315 - 400nm). The skin has a spectral response that is highest for the UVB but drops significantly in the 375-400nm region, so you'll have to try pretty hard to get a tan in the cockpit. If you think of a glider canopy as an SPF100 layer, you won't be far off.

Acrylic blocks practically all UVB (280 - 315nm) so you won't be making any vitamin D while under perspex.

Glass is worse; typical float (soda lime) glass has a 50% cutoff around 340nm so lets through around 60% UVA and no UVB. My grandmother spent most of her last years sitting in a warm sunroom and got a pretty good tan.

As previously stated, your biggest danger is in hanging around on a sunny airfield, especially in the southern hemisphere. European pilots are only in trouble if they fly above the inversion which caps the pollution layer ;-)

DH
TX