Why can we see in an anechoic chamber As in this chamber, the sound reflects off the surface and stays at that point until it dissipates. So why does it not happen with light? Is it because of the surface? If yes, then what will happen if we replace the surface with mirrors?
 A: A useful definition of an anechoic chamber is an enclosed volume where the inside surfaces of its walls present a close impedance match to the characteristic impedance of the medium inside the chamber, so that reflections are minimized. This then means that the behavior of an anechoic room is strongly frequency-dependent, because those impedances are frequency-dependent. 
The absorptive baffles that line the walls inside a general-purpose anechoic chamber will be anechoic to both sound waves and radio waves when the physical dimensions of the baffles are of order ~1 wavelength at the lowest frequencies at which the chamber is designed to be free of echoes. So, if the baffle dimensions are about 36" then they will be strongly absorptive at 300 hertz and above for sound waves and 300 megahertz and above for radio waves. 
But for frequencies very, very much higher than radio waves, the anechoic baffles become ineffective- which means that although they strongly absorb radio waves, they reflect light waves- which is why you can see your way around the inside of a general-purpose anechoic chamber. 
To make that chamber anechoic at light frequencies requires you to paint the baffles black, as commented by Solomon Slow above. 
