There's a type of optical filter tape which you can buy that reduces the amount of energy getting in and out - less than 20% goes through, most of it in the vis

There's a type of optical filter tape which you can buy that reduces the amount of energy getting in and out - less than 20% goes through, most of it in the visible spectrum. It has a blueish tint though and really doesn't do much if it's the ambient temperature that's too high.