Amazon has the Woods Outdoor Hardwired Post Eye Dusk to Dawn Light Control w/ Photocell Light Sensor (59408WD) on sale for $4.05 with free shipping on $25+ or with Prime. Home Depot has it for $4.76.

Designed to replace existing photocells to turn lights on / off automatically at dusk / dawn. Can reduce energy bill if outdoor lighting is running during daylight.