Those would be great for blocking the main bulk of the light but I suspect would leak all around the sides and edges. They look identical to the curtains I currently own. I personally like aluminum foil to block out my windows. I apply it with a spray bottle just the bit of mist the foil will stick to the glass and quickly dry away leaving the foil stuck to the glass. It also works very well to reflect the heat where when I had blackout curtains they would radiate heat. I did have the numbers at one point but the difference between black and aluminum foil was massive.