These dim 50–80% of the light, so the rest of the day you still know that everything's working the way it's supposed to! Although if you prefer, you can double 'em to block even more light, or go for the ~blackout edition~. They're completely removable and leave no residue behind, too!
Promising review: "Wish I'd known about these sooner! The cable box in my bedroom is motion activated, so the dang thing lights up my bedroom the minute I roll over or the cat walks by it. I've even mentioned to my cable company I'd like one without a clock, and their response is "really? Everyone's it!". Umm, no, not everyone! I've resorted to putting things in front of it, but then I can't see the clock. Can't win! Enter these babies! I wish I'd have thought of them it myself. Very simple, didn't come with instructions, but anyone can figure it out. Immediately I saw a dramatic difference! Several different sizes, so they can be used and customized as needed." —Kat
Get a sheet of over 100 stickers in different shapes and sizes on Amazon for $4.29. If you have a big clock face you'd like to dim, also check out a similar product that you cut to size, $8.29 for two six by three inch–sheets.