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:
Explanation
Statement 1 is correct: High-Pressure Sodium (HPS) lamps emit light omnidirectionally across a full 360-degree sphere, requiring reflectors to direct beam output downward onto roads. LED lamps are directional solid-state semiconductors that emit focused light in an arc of roughly 180 degrees or less, preventing light wastage.
Statement 2 is incorrect: Sodium street lamps have an operational lifespan averaging roughly 18,000 to 24,000 hours, whereas modern LED street lights typically deliver 50,000 to 100,000 hours of operational life.
Statement 3 is correct: Sodium lamps produce light via an electric arc through sodium vapor, yielding a dominant yellow-orange double spectral emission (D-lines at 589 nm) that is virtually monochromatic with a poor Color Rendering Index (CRI). In contrast, LED lamps offer a continuous broad visible spectrum and superior colour rendition.
Hence, statements 1 and 3 are correct — Option C.