# how can u control the speed of light? [closed]

The light traveling a 3 lake km/sec, but Pls tell me how can a control the speed of light, means can limit the speed like 2 lake km/sec are 1 lake km/sec

Pls tell me equation

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Dear Anil, I'm having troubles reading your question. Can you make it, somewhat more readable? –  Ali Jul 23 '13 at 6:07
Speed of light $c$ in medium is reduced by its refractive index $n$.
$$c=\frac{c_0}{n}$$ where $c_0 = 299\,792\,458\frac{m}{s}$ is speed of light in vacuum. You are asking for a material of refractive index $n=1,5$ which is e.g. the glass BK-7.