The amount of energy radiated per second by an object. For example, a 100 Watt light bulb is 10 times more luminous than a 10 Watt light bulb. The apparent brightness of an object depends on its distance. A distant 100 Watt bulb may appear considerably fainter than a nearby 10 Watt bulb. Important Points about the Inverse Square Law Apparent brightness depends upon the distance to the light source.
Apparent brightness decreases with the square of the distance.