The Lights Out Sleep Mask is suppose to allow your eyes to see only pich black, no matter what the light in the room is. This is accomplished by the unique contour over the nose. The site noted below gives a really thorough review of the product.

“This mask has indispensable for daytime naps or when sleeping in barracks or tents with other people who like to stay up late. I was stationed for a couple months in Qatar and am currently stationed in Kuwait (that’s as much as I am able to tell you without breaking OPSEC). The mask is more effective and comfortable than the other ones I’ve worn. You can open your eyes no matter the time of day and think it’s the darkest time of night. It blocks the light most effectively due to the contour over the nose. With normal masks you get gaps on the sides of your nose, no matter how you try to position it or if it has a nose cut-out. When I got back from basic training five years ago I discovered I liked to take mid-afternoon naps. I found a silly sleep mask, pink with fake daisies on it. I was able to sleep, but I would wake up with my eyes all dried out. I eventually lost it and went through a basic satin sleep mask and also a silk eye mask that had little pillows attached to the bottom edge so it wouldn’t smash your eyes. Once again, though, both of them dried my eyes out something fierce. Since this mask does not press against your eyes, it allows for moisture to draw out out along your eyelashes”

via www.kk.org