DIAGNOSIS The auto-light timer setting has either been manually overridden or glitched. By default, the light should stay on for about 4.5 minutes after door movement.
FIX You can reset the light timer from the wall control. 1) Press and hold the light button for about 10 seconds. You'll see the light on the motor unit flash. 2) Release the button. Now, immediately press the light button again. Each press will change the duration: one press for 1.5 minutes, two for 2.5, three for 3.5, four for 4.5 (the default), and five presses turns the auto-light feature OFF (which might be your current setting). 3) To set it, wait a few seconds after your final press. The opener light will flash to confirm.
IF THAT DIDN'T WORK There's a possibility the control board's relay for the light is stuck closed. Try unplugging the opener for a full minute to perform a hard reset. This can clear a temporary software glitch controlling the light circuit.
HEADS UP If the light is stuck on physically, even when you unplug the opener and plug it back in, that points to a hardware failure. In that case, you'd need to replace the light module or the main logic board—a job for a pro.