these little battery-powered lights up in my barn last year. It's usually before sunrise when I come out to my barn office in the mornings, and these little lights come on automatically to light my path through the storage area of my barn's second floor, between the stair landing and my office door. Despite being used almost every morning, they're still on their first set of batteries (three AAA cells each). This week I bought another set of six ($20 for the set), and I put one up on the outside of my barn door. That's what you see in the photo, lighting up my lock so I can see to put the key in. These lights make no claim about being suitable for outdoor use, so this is a bit of an experiment. At just over $3 a light, I'm not risking much. :)
It's remarkable to me just how well these cheap little things work. They only come on at night, when they're needed – and even then, they only come on when they sense motion. Generally they pick up my presence when I'm about 12 feet away, which is just about perfect for my needs. Once they come on, they stay on for 30 seconds or so after they last sense motion. That means if I hesitate in my walking or fumble for a key, the lights stay on.