UPSC Prelims 2011 Q64: Science & Technology – Energy & Environment
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?
- (a) 1 only
- (b) 2 and 3 only
- (c) 1 and 3 only
- (d) 1, 2 and 3
Answer: (c) 1 and 3 only
Explanation
CFL vs LED: checking the three statements
CFL (Compact Fluorescent Lamp) and LED (Light Emitting Diode) differ in their core technology and efficiency.
| Statement | Verdict | Reason |
|---|---|---|
| 1. CFL uses mercury vapour/phosphor, LED uses semiconductor material | Correct | This correctly describes the core technological difference between the two lamp types |
| 2. CFL's average life span is much longer than LED's | Incorrect | This is backwards: LEDs typically last much longer than CFLs, not the other way round |
| 3. CFL is less energy-efficient than LED | Correct | LEDs are more energy-efficient, converting more electricity into light with less heat loss, compared to CFLs |
CFL vs LED at a glance:
| Point | CFL | LED |
|---|---|---|
| Technology | Mercury vapour + phosphor coating | Semiconductor material |
| Lifespan | Shorter | Longer |
| Efficiency | Lower | Higher |
Answer: (c) 1 and 3 only.
Why each option is right or wrong
- (a) Incorrect. Statement 3 (CFL being less efficient) is also correct, so '1 only' is incomplete.
- (b) Incorrect. Statement 2's lifespan claim is reversed — LEDs last longer, not CFLs — so this combination is wrong.
- (c) CORRECT. Statements 1 and 3 — the technology difference and CFL's lower efficiency — are both accurate; statement 2 reverses the lifespan comparison.
- (d) Incorrect. Statement 2's lifespan claim is false, so 'all three' cannot be correct.
Key point
CFL (mercury vapour + phosphor) is less energy-efficient and shorter-lived than LED (semiconductor-based) — statement 2's claim that CFL lasts longer than LED is the false one.
Remember
CFL: mercury vapour + phosphor, shorter life, less efficient. LED: semiconductor, longer life, more efficient.
Common mistakes
- Reversing the lifespan comparison between CFL and LED.
- Not knowing CFL's mercury-vapour/phosphor mechanism versus LED's semiconductor basis.
- Underestimating how much more energy-efficient LEDs are compared to CFLs.
Exam tip
LED beats CFL on both lifespan and efficiency. Any option claiming CFL lasts longer is a reversal trap.
Sources
- Bureau of Energy Efficiency, Government of India — Standards and Labelling Programme: Compact Fluorescent Lamps
- Encyclopaedia Britannica — light-emitting diode