Kommentar zu Könige I 6:4

That were open [wide] on the outside and closed [narrow] on the inside. Our Rabbis explained [שקופים] as an expression of looking, an opening, an observation;⁷It was made of a glass-like substance.—Metzudas Dovid. open on the outside and closed on the inside, narrow on the inside, not in the usual manner of other windows⁸Alternatively, חלוני means “sockets” into which שקפים [=“horizontal beams”] were inserted. The sockets were open only on the inside and did not go all the way through the wall, i.e., they were אטומים [=sealed] and not visible from the outside of the building. which are made for illumination,⁹They are therefore constructed narrow on the outside and widening towards the inside to allow the light to spread out as it enters. to indicate that it was not in need of illumination.¹⁰See Maseches Menachos 86b.