Target sells solar lights that stick into the ground around your garden or walkway. After charging all day from the sun, they turn on by themselves all night & stay on till morning. But they don't use up your electricity. It's nice to have a little light on all the time.
For security purposes by the front or back door, you can get a floodlight with both a light sensor AND a motion sensor. So it stays off during the day, but comes on at night only if someone comes in range of the sensor. Then it stays on for like 5 minutes.
These are great for the backyard, where no one goes. If the light turns on, you know someone is back there. You can set the sensor so it doesn't go on if something as small as a dog crosses in front of it. Otherwise, you can leave the power on all the time & forget about it.