# What is the speed of light in water?

The speed of light in water is approximately 225,000 km per second. While enormously fast, this is notably slower than the speed of light in a vacuum, which is 300,000 km per second.

The degree that light slows down when passing through a medium is described by the index of refraction of that medium. This index measures how much the medium alters the course that the light travels through reflection, refraction, occlusion or other obstruction. Calculating the speed of light in the medium requires dividing the speed of light by the index of refraction. This results in the equation v = c / n, where v is the speed that light travels in the medium, c is the speed of light in a vacuum and n is the index of refraction.

Reference:
Q&A Related to "What is the speed of light in water?"
 As you and I both obviously know, the speed of light is very much dependent on what medium it is traveling in. Light tends to travel at speeds of 140,000 miles per second in water http://www.ask.com/web-answers/Science/Physics/wha...
 Its slows slightly as it hits the water, at the same time it also bends. http://wiki.answers.com/Q/What_will_happen_to_the_...
 c/v =rm/r0. v is velocity of light in medium. c is in vaccum. rm is 1. r0 is 1.33. v is (3/1.33) x 10^8 m/s. = 2.256 x 10^8 m/s. http://answers.yahoo.com/question/index?qid=201201...
 A pilot light is a somewhat outdated way to light a water heater or any other gas burner. A small flame is kept burning all the time. When the water heater needs to turn on, this http://www.ehow.com/about_5059218_causes-out-hot-w...