The sensitivity of motion sensors in motion detector lights varies, and there's a good chance yours aren't set exactly how you want them right out of the box. That's why manufacturers allow you to adjust motion lights, so you can set the sensor to read movement at the direction and in the area where you want. Take time to test your motion sensor lights before you finish installation and you'll find that with proper adjustments, your motion sensor lights work just the way you want them to.
Look for the "Sensory Adjustment Dial," located on the bottom of your motion light fixture. Rotate the dial to "Medium" then slide the switch to "Test."
Turn the light switch that powers that fixture to the "On" position to send power to the fixture and stand out of the way of the motion sensor. Your motion lights will turn on for about 30 seconds after you turn on the switch, then the lights will turn off. If the sensor detects motion, the lights will stay on as long as they detect motion.
Use your hand to adjust the motion light sensor so it points in the direction you want.
Test your aim by walking in the area where you want the motion detector light to detect movement, and then see if the lights turn on.
Tweak your motion light using the "Sensory Adjustment Dial." Rotating the dial to the "High" position means your motion sensor will detect movement at greater distances than your original test. Rotating the dial to the "Low" position means the motion sensor will detect movement at lesser distances than your original test.
Slide the switch off of "Test" mode and back to its regular operation mode.