UPSC CSE Prelims
Question 88
With reference to street-lighting, how do sodium lamps differ from LED lamps?
- Sodium lamps produce light in 360 degrees but it is not so in the case of LED lamps.
- As street-lights, sodium lamps have longer life span than LED lamps.
- The spectrum of visible light from sodium lamps is almost monochromatic while LED lamps offer significant colour advantages in street-lighting.
Select the correct answer using the code given below.
View correct answer and explanation
Correct answer: C
Correct Option: C (1 and 3 only)
Explanation: Sodium lamps radiate broadly from a source and emit characteristically narrow yellow spectra; LEDs are directional, longer-lived and offer versatile colour rendering.
Statement / Pair / Item-wise Analysis:
1. Correct / qualifies - Conventional sodium bulbs radiate nearly all around; LED modules direct light more easily.
2. Incorrect / does not qualify - LED streetlights generally have much longer rated service life than sodium lamps.
3. Correct / qualifies - Low-pressure sodium light is nearly monochromatic; LEDs permit better colour rendering.
Option-wise Analysis:
A. Incorrect-omits valid item 1 (Conventional sodium bulbs radiate nearly all around; LED modules direct light more easily).
B. Incorrect-includes item 2, which is not valid (LED streetlights generally have much longer rated service life than sodium lamps); omits valid item 1 (Conventional sodium bulbs radiate nearly all around; LED modules direct light more easily); omits valid item 3 (Low-pressure sodium light is nearly monochromatic; LEDs permit better colour rendering).
C. Correct-selects exactly the supported statements/items: 1, 3.
D. Incorrect-includes item 2, which is not valid (LED streetlights generally have much longer rated service life than sodium lamps).
Review note: High-pressure sodium lamps have a broader spectrum than low-pressure sodium; the exam generalisation is clearest for low-pressure sodium.