Speed of light in a vacuum ~ 300.000 Km/s
In metric units, the speed of light in a vacuum is 299,792,458 metres per second (1,079,252,849 km/h).
In imperial units, the speed of light is about 670,616,629.4 miles per hour or 983,571,056.4 feet per second (roughly one foot per nanosecond), which is about 186,282.397 miles per second.
Light traveling through a medium other than a vacuum travels below c as a result of the time lag between the polarization response of the medium & the incident light.
