text: now tell me what will be the speed seen by one photon of other in a beam? no impressive answers as accroding to relativity for every frame of referrence velocity of light is same =3*10^8m/sec so another photon should see the same the speed of one photon seen by other photon is zero if the beam is perfectly coherant.but if the beam is incoherant then the speed varies accordingly. the speed of light is about 300 million metres per second. two photons are said to be coherant if they travel in the same direction and vibrate in exactly the same way.