Question

Choose the correct option regarding luminous objects
A. All objects which glow are luminous objects
B. Objects which is not source of light is luminous objects
C. Objects which glow can be luminous objects
D. None of the above

Answer 1

Luminosity of an object can be understood by whether it emits light of its own. Emitting light and glowing are two different things, even if we glow in presence of light but that doesn’t mean we emit our own light.

Complete answer:
To understand luminous objects, let us first understand luminance, which is the measure of luminous intensity along a given direction and unit area. Luminance describes the amount of light that is reflected, or emitted or passes through a given area.
We know that light is an electromagnetic radiation and an object is considered as luminous or non-luminous based on the electromagnetic or radiant power emitted by it. If an object emits its own light, then it is called a luminous object and if not, then it is called a non-luminous object.
The Sun is an example of a luminous object as it glows by emitting its own light unlike the Moon which glows by reflecting the light rays coming from the Sun.
Hence, option c is the correct answer.
Additional information:
There are many examples of luminous and non-luminous objects around us. Candles, light bulbs, torches, etc. are luminous objects whereas the Earth itself is a non-luminous object which glows by reflecting the rays coming from the Sun. Humans themselves are non-luminous and require luminous objects to be able to see.

Note:
Luminous objects can be natural and can be artificial. The word glow should not be confused with the luminosity of the object. Things glow in the presence of light and luminous objects are the ones who emit light.