If I am inside at night with a light on, will someone outside be able to see inside?

All one way films work well during the day, but at night they can reverse the effects. When it is bright inside and dark outside, you will be able to see into the room/house somewhat. There currently is no one way option that works 100% of the time, they are all based on the lighting situations. Consider ordering some samples to see what films are right for you.