Just How Fast is Light, Anyway?
|In||Light Travels About*|
|1 second||186,000 miles = 300,000 kilometers|
|1 millisecond||186 miles = 300 kilometers|
|1microsecond||1000 feet = 300 meters|
|1 nanosecond||1 foot = 30 centimeters|
|1 picosecond||12 mils = 300 microns|
*In free space; in a wire and especially in coaxial cable, the speed of signals can be much slower. Common coax cables have "velocity factors" from 0.85 to 0.66 -- meaning that electricity (which in free space moves at the same speed as light) travels only 85 to 66 percent as fast through those cables.
While "a nanosecond per foot" is close enough for most applications, the actual value is 1.01690688 nanoseconds per foot.