flash on someone or something
[for a light] to shine on someone or something suddenly or in bursts. The orange neon light flashed on John's face, making him look quite strange. The light flashed on the window shade, startling the occupants of the room.
flash on something
Sl. to remember something suddenly and vividly. Then I flashed on a great idea. I was trying to flash on her name, but I couldn't bring it to mind.
[for a light] to turn on suddenly. The light flashed on and woke us up. When the light flashed on, I had just been getting to sleep.