Laser pointers can light your path or entertain your cat, but pointing a laser at an aircraft is dangerous and illegal. And a Florida man who pointed a laser at a police helicopter is now serving a prison sentence thanks to an investigation by the FBI and local law enforcement.

During an armed standoff in a Pasco County, Florida, neighborhood on December 5, 2017, the sheriff’s office called for a helicopter to assist deputies. As the helicopter hovered overhead, Ryan Fluke, 28, repeatedly aimed a laser pointer at the helicopter, momentarily disorienting the pilot.

The pilot recovered his vision, but had he not, the results could have been disastrous. While airborne, though, the pilot had been able to determine the house where the laser beam originated, and, after landing, went to the residence. Fluke, who was at the house and matched the description of the man captured on the helicopter’s video surveillance recordings, was arrested.

When confronted by law enforcement, Fluke apologized. “He said he didn’t know it was so bright,” said FBI Special Agent Katie Hill, who worked the case out of the FBI’s Tampa Field Office.

In November 2018, Fluke pleaded guilty to aiming a laser at a police helicopter; he was sentenced in March 2019 to 21 months in federal prison.

While pointing a laser at a helicopter or plane may seem harmless, the opposite is true. It’s dangerous—both to those in the air and on the ground—and it’s a federal crime.

“It’s very risky to point lasers at aircraft,” Hill said. “Whether it’s a helicopter or a large commercial airliner, it’s very dangerous. It’s especially dangerous on takeoff and landing, which are critical times of the flight.”

The Federal Aviation Administration (FAA) tracks these incidents and received 6,754 reports of laser strikes in 2017—a 250 percent increase since the FAA first started tracking laser incidents in 2010.