Light is a form of energy and can be transformed into other forms of energy. You would have observed the path of 'a beam of light' inside a room. This beam is nothing but the scattered light produced by the dust particles and this beam of light becomes invisible if the room is dust free. Thus light makes things visible even though light by itself is invisible.
Light does not require a material medium for its propagation. In a given medium light travels with a very high but finite velocity. The velocity of light in air or vacuum is 3 x 108 m/s.
