For one thing I can never remember how far a piece of light travels per second.

In other words, while within the device, light travels as if it were present.

As light travels from one medium to another, it changes speed.

When you see something under water, light travels differently from seeing it in the air.

This is simply defined as the distance that light travels in one second.

But light travels at 300,000 kilometers in a second, almost a million times the speed of sound.

In the vacuum of space, light travels at a constant 186,171 miles per second.

We see the lightning first, he said, because light travels much faster than sound.

Make a laser so that the light travels in a circle.

We don't know why light travels at a constant speed forever.