“Every night, when you turn off my light, the colors go away,” says Yo. “Look! My red train is black and my green ball is gray.”
“When there isn’t much light,” says Mom, “the parts inside our eyes that help us see colors stop working.”
“But if I turn up the light a little with the dimmer switch . . .” “Ha!” says Yo. “Now there’s red in my train and green in my ball.”
“When I turn the light all the way up, everything will be bright and colorful,” says Mom.
“Unless I hide under the covers,” says Yo, “then everything is black, black, black.” “When there’s no light, we can’t even see the shapes of things,” agrees Mom. “So it’s important to leave the hall light on and…