Speed of light The speed of light in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics Its exact value is ,, metres How Fast Does Light Travel The Speed of Light The speed of light in a vacuum is , miles per second , kilometers per second , and in theory nothing can travel faster than light In miles per hour, light speed is, well, a lot How Fast is the Speed of Light NASA A traveler, moving at the speed of light, would circum navigate the equator approximately . times in one second By comparison, a traveler in a jet aircraft, moving at a ground speed of mph, would cross the continental U.S once in hours. speed of light Definition Equation Britannica Speed of light, speed at which light waves propagate through different materials In particular, the value for the speed of light in a vacuum is now defined as exactly ,, metres per second traveling at the speed of light Scientists simulating traveling at the speed of light. Speed of light Simple English , the free The speed of light in empty space is a universal physical constant This means it is the same everywhere in empty space and does not change with time Physicists often use the letter c to denote the speed of light in empty space vacuum It has the value ,, meters per second or about ,. miles per second. Speed of light Define Speed of light at Dictionary speed of light The distance light can travel in a unit of time through a given substance Light travels through a vacuum at about , miles, or , kilometers , per second.