Light that helps us see. Light travels at the universal speed, whether from a light bulb to the eye or from a torch to the sock in the cupboard and then to the eye.
Light always travels at about:
300 million metres in each second or: 3 × 108 metre / second
That's the universal speed, often called the speed of light
. In deep space that's just what it does. When light travels through air, water or glass (three examples of different mediums) it appears to travel more slowly.
Some speeds of travel: vacuum, 299 792 000 metre/second ; air, 299 703 000 metre/second ; water, 225 408 000 metre/second ; glass, 199 862 000 metre/second.
Because light travels at such a high speed, seeing books, cars and dogs seems to happen without delay. Only if you look at things very far away do you notice the delay.