We can see any object, when light reflected by that object reaches to our eyes. But in the dark room, no light is reflected by the object. Hence, we are not able to see the objects in dark room. But if there is light outside the room, we can see the objects lying out there.
When a light ray falls on any object, it is bounced back from the object. This process is known as the Reflection of light. The light reflected from the object falls into our eyes, making the object visible to us. All the things we see around us are because of reflection.
The reflection of light depends on the type of object. A polished or smooth surface reflects most of the light falling on it, while a rough surface absorbs some amount of light and reflects back the rest of the light. The direction of reflected rays depends upon the surface of the object.