Editorial Feature

The Speed of Light - Basic Facts and Figures

The speed of light is one of the fundamental constants of physics and is measured as exactly 299,792,458 metres per second or 1,079,252,848.8 km/h.


The speed of light is denoted by the constant, c, which comes from the Latin for swiftness, celeritas. This definition of the speed of light is its speed in a vacuum and does not only apply to just visible light. The speed of light determines the speed of all wavelengths of electromagnetic radiation and is the theoretical maximum speed that can be achieved by anything in the Universe.


The speed of light is one of the components of Einstein’s famous theory of special relativity. Using this theory, it is possible to understand that the speed of light represents a speed limit that cannot be surpassed. For an object of constant mass, increasing its speed also increases the energy required for the system at a rate that is proportional to the square of its speed.

Einstein's Theory Holds Up

So far, no events that violate Albert Einstein's principles of special relativity have been found. This theory has had many important implications in physics, such as the prediction of phenomena like gravitational waves and lenses.  

This article was updated on 5th June, 2019.

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