A motion light is an inexpensive and easy way to deter trespassers from violating the boundaries of your property. Most motion lights run through a warm-up process when they're installed. In the event of a power outage, the light may lose its set-up and stay on all the time or not come on at all. Resetting a motion light is a fairly straightforward process that can take only a matter of minutes. There are no tools required for the job.
Inspect the sensor or photo cell on the light, making sure neither is covered up in any way. If the power outage was caused by a storm, the same storm could have deposited debris on the photo cell.
Turn off the circuit breaker for 30 minutes. Make sure the switch for the light in the on position. Turn on the breaker. The light will come on. It should shut off and work normally.
Replace the sensor on the light if nothing else has worked. Power surges can damage the sensor. Check the owner's manual for the proper sensor. You'll find replacements at home improvement stores.