I was parked at lunch and could have sworn I had 4 bars of fuel. When I got back and started it, I had zero bars and the fuel warning light was on. After driving for a bit, I got 3 bars of fuel and still warning light. It was parked on the side of the street whic wasn't level of course. How many bars of fuel left until the warning light usually comes on. For me it is usually 1 bar.

 

2 bars for me, sometimes 3.

 

I made a similar observation recently myself. The fuel gauge dropped to 1 bar and the light came on then a short while later the gauge registered 2 bars but the light stayed on. I assumed that once the light is illuminated it stays on until you fill the tank.