You can use an outdoor projector during the day, but it won't provide the best viewing experience. In fact, you have to wait about half an hour after sunset until ideal viewing conditions set in, and even then, ambient light can ruin the effect. If you really want to use your outdoor projector during the day, and you're okay with the fact that the picture will look washed out, it's important to choose a projector that's really bright. "You'll need one that's at least 3000 lumens," says Prouty. You'll be able to see the picture at that brightness, although it may still look washed out. Prouty also advises that "you'll likely have better success with laser projectors as they generally have a brighter output than LED projectors."