Question

There is a electric bulb turned on in a room , with no other light falling on it.Then how are we able to see the bulb?

Answer 1

For us to be able to see an object,

   1.  either the object emits (radiates) light waves (electromagnetic waves in the visual spectrum from violet to red), that falls in our eyes.
         example:  Sun,  bulb when on.

   2. or, the object reflects or scatters light falling on it into our eyes.
           example:  Moon, table,  Blub when off

The filament is made of a nichrome metal, which is heated to nearly 2000 deg C, and then it becomes bright white or bright red.  It radiates energy in light waves (or particles called photons).   The electrical resistance in the filament dissipates  heat and so filament heats up.