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 a longer lifespan 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:

The correct option is 1 and 3 only.

Let us analyze each statement step-by-step with reference to sodium lamps and LED (Light Emitting Diode) lamps used in street lighting:

Statement 1: Sodium lamps produce light in 360 degrees but it is not so in the case of LED lamps.
This statement is correct. High-Pressure Sodium (HPS) and Low-Pressure Sodium (LPS) lamps are omnidirectional light sources, meaning they emit light in all 360 degrees around the bulb. LED lamps, on the other hand, are directional light sources and emit light in a specific direction (typically 180 degrees or less), making them more efficient for targeted street illumination without needing external reflectors.

Statement 2: As street lights, sodium lamps have a longer lifespan than LED lamps.
This statement is incorrect. LED lamps generally have a much longer lifespan compared to sodium lamps. Typical sodium lamps last around 12,000 to 24,000 hours, whereas LED street lights can last 50,000 to 100,000 hours or more, significantly reducing maintenance and replacement costs.

Statement 3: The spectrum of visible light from sodium lamps is almost monochromatic while LED lamps offer significant colour advantages in street lighting.
This statement is correct. Sodium lamps (especially Low-Pressure Sodium lamps) emit light almost exclusively at specific yellow-orange wavelengths (around 589 nm), making their emission spectrum nearly monochromatic and resulting in very poor Color Rendering Index (CRI). LED lamps produce a broad spectrum of white light, providing superior color rendering, improved visual clarity, and better night vision safety on roads.

Therefore, statements 1 and 3 are correct, while statement 2 is incorrect.