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?

The correct answer is C (1 and 3 only). Here is how each statement fares.

• Statement 1 is correct. A CFL (compact fluorescent lamp) works by passing an electric discharge through mercury vapour, which emits UV light that the phosphor coating converts into visible light. An LED is a semiconductor device that emits light when current crosses a p-n junction.
• Statement 2 is wrong. The reverse is true. A CFL typically lasts about 8,000 to 10,000 hours, while an LED typically lasts 25,000 to 50,000 hours or more.
• Statement 3 is correct. An LED produces more lumens per watt (roughly 80 to 150 lm/W today) than a CFL (roughly 50 to 70 lm/W), so the CFL is less energy-efficient.

The core concept is the difference between gas-discharge and solid-state lighting. This links to the Mains theme of energy efficiency and e-waste, since CFLs contain mercury and fall under the Minamata Convention's phase-down rules, a point you can use in GS-III answers.

Trap: Candidates often assume that 'energy-saving' CFLs are the longest-lasting and most efficient option, and reject statement 3 without checking. Remember that LEDs have overtaken CFLs on both life and efficiency.