Glass blocks/reflects too much light.

I am making a cupboard that has doors that are made of glass with a wooden frame around them. I assigned the 4 mm thick glass planes a material that only has a simple Glass BSDF shader (Beckmann, 1;1;1, 0, 1.45) and instead of getting something like this I get this It’s almost like light can’t even penetrate the glass. Is there a way to solve this problem?

Light cannot penetrate glass. Not without refractive caustics anyway. If you’ve turned off caustics you need to fool Cycles. The trick is to use a light path node in the end to mix your glass shader with a transparency shader. Use the IsShadowRay output.