UPSC Previous Year Question | Prelims GS | 2021

With reference to street-lighting, how do sodium lamps differ from LED lamps? 1. Sodium lamps produce light in 360 degrees but it is not so in the case of LED lamps. 2. As street-lights, sodium lamps have longer life span than LED lamps. 3. 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.

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

Answer

Correct Answer

1 and 3 only

Explanation

Sodium lamps emit near-monochromatic yellow light in all directions (360 degrees), whereas LEDs are directional and offer better colour rendering (statements 1 and 3). LEDs generally last longer than sodium lamps, so statement 2 is incorrect.

Topics: lighting technology, physics, science & technology, sodium lamps vs led street lights