Why can’t you see in the dark?

Xiao Fang and his grandfather took a train to travel. Along the way, Xiaofang looked at the charming scenery outside the window and asked this and that. Grandpa patiently answered Xiaofang’s various questions. It was getting dark. The scenery outside the window became increasingly blurry, until it was completely dark and nothing could be seen clearly. Xiao Fang sat down next to his grandfather. Grandpa said: "You have no problem this time, right? It's time for me to take a break." Xiao Fang said mischievously: "Yes! Yes! Why can't I see things outside the window at night?" Grandpa said: "We look at things, We use our eyes to feel the color, shape, size and distance of things. However, the color of things can only be expressed when there is light. Some things that can emit light, such as the sun, light bulbs, candles, and fires, are emitting light. We can see them, but most things don't emit light and we can see it. That's because when light shines on them, part of the light is reflected back and shines into people's eyes. Look, we can see everything when the lights are on in the carriage. Smooth, shiny, and light-colored things absorb less light and can reflect a lot of light; rough, dull, or dark-colored things can absorb a lot of light. Absorbs most of the light and reflects very little." Xiao Fang seemed to understand something. He asked: "Grandpa, can red things reflect red light? Yellow things can reflect yellow light?" Grandpa said: "You can say that." Xiao Fang asked again: "Grandpa, do blind people not know what colors are?" Grandpa said: "That's right, because their eyes have no feeling for light." Just as he said that, the lights in the carriage were turned off. Suddenly, Xiaofang couldn't see anything and slowly fell asleep.