How can a robot see a dark line on the floor?

Picture a little robot rolling across a white floor, following a black line wherever it bends. You might have seen one at school or in a video. Yet a robot has no eyes like yours. So how can a robot see a dark line on the floor?

Let's peek under the robot, near its front wheels. Close to the floor sits a small lamp that shines its light straight down. The lamp lights up the patch of floor right under the robot, so the robot can check that spot.

When light hits the floor, it bounces back up, like a ball bouncing off the ground. A white floor sends lots of that light bouncing back up toward the robot.

Right beside the lamp, the robot carries a sensor, which means a part that feels how much light reaches it. Over the white floor, lots of bounced light lands on the sensor. Now, what do you think the sensor feels when the robot rolls over the dark line?

The dark line soaks up most of the light from the lamp. Only a tiny bit of light bounces back, so the sensor feels just a faint glow. That change from bright to faint is what the robot needs.

The sensor keeps telling the robot's computer how much light it feels, many times every second. That way the computer always knows what lies right under the robot.

The computer follows one simple rule. Lots of light means white floor, and only a faint glow means the dark line is right underneath. That is how the robot sees the line, with a lamp and a sensor instead of eyes.

Today's key word is sensor. A robot sees a dark line because its lamp shines down, and its sensor feels much less light bouncing back from the dark line than from the white floor.

Sleep well, clever explorer, and dream of robots rolling gently along their lines.