Blackout Shades: Block All Light
If you want to completely block out light from a window, the best option is adding a blackout shade or liner. Often referred to as room darkening shades, these offer complete privacy at all times of day, let in no light, and offer no exterior view when lowered.
The reflective finish of one way privacy window film gives the glass a one way mirror effect when there is more light on one side than the other. This means that, during the day, people on the outside of the window can't see in through the glass, while you can still see clearly through it from the inside.
To deliver one-way privacy, the most effective and popular course of action is the application of a reflective film. Once applied, the film will give the exterior side of the glass a mirrored effect during daylight hours, preventing vision through the glass, whilst maintaining the view from the inside out.
Add Vinyl Light Gap Blockers
Light blocking strips (or Light Blockers) are an adhesive vinyl strip that can be attached to your window frame and will obstruct those pesky gaps. These are typically used in tandem with blackout window treatments but can be used to simply reduce the light coming in from the sides.
Aluminum foil is probably one of the cheapest ways to blackout the windows in your home. With one roll, you should be able to cover the windows in your room and still have enough leftover to wrap the kids' sandwiches for school. The foil will reflect the light as it tries to make its way through your windows.
Solar shades are designed to allow you to see out, but other's not see in, providing daytime privacy. The exact opposite is true at night! When a light is on in the room, people outside will be able to see directly into your home.
WINDOW FILM
First, thoroughly wash the surface to be frosted, using glass cleaner and a lint-free cloth. Next, combine water with a couple drops of dish detergent in a spray bottle. Then proceed to lightly spritz the glass before applying the window film. As you go, remove air bubbles with a squeegee.
At night, the window film will block about 95% of the light to give you a high level of privacy. During daylight hours, any ambient light will reflect the mirror film's surface, making it impossible to see inside. Yet, at the same time, you will be able to see outside.
Ultimately, you can't force one-way mirror tint to work at night. It's just not physically possible if you still want to be able to see outside of the window. You can do things to make the film more reflective at nighttime—reduce interior light, add outdoor area lighting—but it will never match the sun's intensity.
Frosted glass, tissue and other materials aren't opaque, but we can't see through them because they scatter light so that that any image seen through them is hopelessly blurred.
During the day you can see out but, passers-by can't see in. However, at night the effect is reversed. When the lights are on in your home at night, it makes the shades transparent.
Vertical blinds offer great control for light and privacy. By drawing back the blinds you can let in maximum light, bringing the outdoors in. However, you can easily balance the need for light and privacy by angling the louvres. As well as being ideal for windows, vertical blinds also work well for bi-fold doors.
Aluminum foil on windows is most effective at keeping out heat and light when you place it shiny side out and cover its backside with a layer of something else, like insulation or cardboard.
Can aluminum foil damage windows? Yes, but on bare minimum. The only damage an aluminum foil can do to damage windows would be small scratches that a glass buffing material can always fix. Other than this, aluminum foil on windows is generally safe to use for wrapping windows.
What's the purpose of covering windows with tin foil? To Stay Cool: The most common reason people line their windows with tin foil is to keep their house protected from the sun's rays — and the radiant heat associated with them.