# How is the speed of light measured

## Measuring the speed of light - how does it work?

In this article we will show you how to measure the speed of light. The light travels at an almost unimaginable 299,792.458 kilometers per second. Measuring such a high speed is astonishingly simple.

### Measure the speed of light - this is how it works

A method to measure the speed of light is particularly accurate and not too difficult to implement. This method was used by Léon Foucault as early as 1850 to get a very precise estimate of the speed of light.

• Put simply, we calculate the speed of light nowadays with a laser, a mirror and a stopwatch that is as accurate as possible.
• For example, the mirror is placed 100 meters away from the laser. The laser is then aimed at the mirror and the stopwatch is connected to the laser.
• For the actual measurement, the laser and the stopwatch are switched on at the same time. As soon as the light has reached the laser again (since it is reflected by the mirror), the stopwatch stops.
• Now all you have to do is read how long it took the light to cover the distance. This can then be used to calculate how fast the light is.