Depending on the windows you have and the type of blind you choose, light leakage will not always be an issue on blinds hung inside of the recess; for instance, if your window has generous mullions or wide-ish sides of the frame, and the blind itself sits close to the window.

Outside mount means the window treatment is mounted on the wall above (or outside) the window frame.

For a blind to block light entirely, it needs to be made from an impermeable or blackout material, fit the window properly, and have enough of a margin around it to prevent light leakage. This will aid in the process of maximum light blockage due to the fact that window blinds that are too short or not wide enough in length will let in a great amount of sun rays.

You need two light-blocking things on any window to properly block light because light is very good at getting past stuff. Easy fitting multi pack set - We provides several length combos for the light blocking strips, making it easier to fit all window types or doors. The product is doing what it is promised and I would recommend this product for anyone that needs to have total black out experience at night to sleep. Window frames can be off square, shades may not hang perfectly straight, the shade may have not be measured correctly.The reason being is that an outside mount provides better coverage over the entire window which leads to less spaces for light to come through. Only things that really work are (1) wooden shutters like you get in Georgian houses, and (2) those roll down external blinds you get in continental Europe. These versatile tracks are designed for use with most window shades and come in two convenient options: Removable (magnetic) for flexibility or Permanent (foam tape) for a secure, lasting solution. We recommend selecting light blockers for most inside mount roller shades since rollers have the largest light gaps due to the nature of their fabric's construction.