The light is absorbed by the surfaces within the room. All materials absorb and reflect light to some degree. It is the part or parts of the spectrum that are absorbed or reflected that decides which 'colour' we see. Put simply a green surface absorbs all the blue, red, orange etc parts of the visible spectrum and reflects green. In theory, a white surface reflects all light and a (matt) black material absorbs all light. However, in practice, there is no such thing as either a perfect 'reflector' or 'absorber' as some of the light will always be absorbed / reflected. In theory, a room lined with 100% reflective mirrors would continue to be 'lit' perpetually even after you switch the bulb off. However, you wouldn't be able to see this 'perpetual effect' as your retinas (or the light sensitive surface of a camera) would absorb this residual light the moment you looked at / filmed it. (And that's ignoring the light that would be absorbed by the bulb and wire material.!)