Question

Why is the luminous efficiency small for a filament bulb as compared to a mercury vapour lamp?

Answer 1

Answer:

The filament bulb has lower luminous efficiency because most of its output is heat in the infra-red range. The mercury vapor lamp wastes very little in the infra-red range. Instead, it produces light in the green and blue range (with a little of ultraviolet).

Answer 2

The luminous efficiency small for a filament bulb as compared to a mercury vapour lamp because, the filament bulb is less efficient.

Explanation :                                              

Reason is as follows below  :

• The filament bulb is less efficient because most of the heat is in the infrared range.
• Mercury lamps waste very little in the infrared range.
• Instead, it emits light (with a small amount of ultraviolet light) in the green and blue areas.

Thus, the reason has been explained.