Question

What are primary and secondary sources of light? Answer briefly.

Answer 1

Hint Primary sources of light do not require to be in the presence of other sources of light to be seen. Secondary sources cannot be seen without the presence of other sources of light.

Complete step by step answer
In observing the world around us, we need light from objects to be incident on our eyes then interpreted by the brain. For example, to see a table, light rays from the table have to be reflected into our eyes. When this table is placed in a dark room, it cannot be seen, even if the observer is standing in a bright room. However, some objects when placed in the dark can still be seen because they create their own light. Such objects are said to be luminous and are classified as primary sources of light.
Generally, primary sources of light are objects which can generate their own light. Examples include the sun, a bulb and a flame. These sources of light since they create their own light do not need the presence of other sources of light to be seen in the environment. Any other sources of light not in this category are called secondary sources of light
Secondary sources of light are objects which do not generate their own light. These objects are said to be non-luminous. Examples include, the moon, a table, or a candle wax, and as a matter of fact most objects around us. Non-luminous objects are seen by a reflection of the light incident on them from primary sources.

Note
In application, because they generate light, luminous objects are used in the homes to illuminate the surroundings.
Also luminous objects are luminous due to some phenomena which occur in nature such as Blackbody radiation (bulb), Reverse photoelectric effect (X-ray), nuclear reaction (sun), chemical reaction (flame). Some non-luminous objects can also be made luminous through these phenomena. For example, through blackbody radiation, a simple iron rod can be made to glow if placed in extreme heat (like fire) for a time.