Glass definitely is not conductive. Look at the top of your telephone pole. The wire is wrapped around glass that is screwed on to metal, at least if your power lines are old. It is also a very good insulator against heat but wont work for your application. As someone already mentioned, you are losing lumens, but an inconsequential amount if the glass isn't too thick. While that is going on though, you are also filtering out harmful UVB and UVC radiation that is wreaking havoc on your plants DNA. That said, it isn't going to make your grow room cooler. It may take some heat stress off the meristem, but it is only reflecting it out to your grow area.