UPSC Prelims 2011 · Question 74 of 100

UPSC Prelims 2011 question on CFL vs LED

What is the difference between a CFL and an LED lamp?

1. To produce light, a CFL uses mercury vapour and phosphor while an LED lamp uses semi-conductor material.

2. The average life span of a CFL is much longer than that of an LED lamp

3. A CFL is less energy-efficient as compared to an LED lamp.

Which of the statements given above is/are correct?

  1. 1 only
  2. 2 and 3 only
  3. 1 and 3 only
  4. 1, 2 and 3
Show answer

Answer: C. 1 and 3 only

Verdict

Correct Answer: 1 and 3 only

Statements 1 and 3 are correct because LEDs use semiconductor technology and are more energy-efficient, while CFLs do not have a longer life than LEDs.

Analysis

LED lamps are more energy-efficient and environmentally safer than CFLs. The main difference lies in their working mechanism, lifespan and energy use.

Statement by statement

1. CFLs use mercury vapour and phosphor, while LEDs use semiconductor material — Correct

CFLs produce light by passing electricity through mercury vapour, which creates ultraviolet light.

This ultraviolet light then strikes a phosphor coating and produces visible light. LEDs use semiconductor material to emit light directly when current passes through them.

2. Average life of CFLs is much longer than that of LEDs — Incorrect

This statement is reversed.

LEDs generally have a much longer lifespan than CFLs. CFLs usually last around 8,000–10,000 hours, while LEDs can last around 25,000–50,000 hours.

3. LEDs are more energy-efficient than CFLs — Correct

LEDs convert more electrical energy into light and waste less energy as heat.

A lower-watt LED can often produce the same brightness as a higher-watt CFL.

Extra UPSC info

* CFL stands for Compact Fluorescent Lamp.

* LED stands for Light Emitting Diode.

* CFLs contain mercury, making disposal environmentally sensitive.

* LEDs are mercury-free and more durable.

* LEDs give instant full brightness, while CFLs may take time to warm up.

* UJALA scheme promoted affordable LED bulbs for energy efficiency in India.

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