Speed of light

Licenced under the Creative Commons Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0) licence: http://creativecommons.org/licenses/by-sa/3.0/

AVR-based real-time speed-of-light display

Calculating the speed of light

The speed of light (v) is calculated from the speed of light in vacuume (c) and the refractive index (n) of air¹ based on the current measures of temperature, relative humidity and atmospheric pressure².
Factors such as the wave length (λ) of the standard red helium-neon laser in vacuum and the concentration of CO₂ in the air has not been taken into account (this calculation is valid for λ≈633nm and the approximate concentration of CO₂ of [300..600]μ/mol/mol), although this would yield a more precise calculation of the speed of light.
The included factors are taken from Yahoo!'s weather API³.

¹ http://www.rpi.edu/dept/phys/Dept2/APPhys1/optics/optics/node4.html
² http://emtoolbox.nist.gov/Wavelength/Documentation.asp
³ https://developer.yahoo.com/weather/