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.

Answer: C. Statements 1 and 3 are correct; Statement 2 is wrong. SODIUM-VAPOUR LAMPS (low-pressure / high-pressure sodium) versus LED (Light Emitting Diode) lamps in STREET LIGHTING: Statement 1: CORRECT. SODIUM LAMPS EMIT LIGHT IN ALL DIRECTIONS (360°) because they are GAS-DISCHARGE LAMPS where the entire vapour column glows. Most of the light wastes upward and sideways, requiring reflectors to direct light to the road. LEDs are SOLID-STATE SEMICONDUCTOR DEVICES that emit light in a forward HEMISPHERICAL CONE (~120-180°) from the chip, NOT 360°. This makes LEDs INHERENTLY MORE DIRECTIONAL and efficient at putting light where needed (the road), reducing light pollution. Statement 2: WRONG. SODIUM LAMPS DO NOT have a LONGER lifespan than LEDs — the OPPOSITE is true. Typical lifespans: - HIGH-PRESSURE SODIUM (HPS) lamps: 24,000-30,000 hours. - LOW-PRESSURE SODIUM (LPS) lamps: ~18,000 hours. - LED street lights: 50,000-100,000 hours (sometimes up to 150,000 hours). LEDs typically last 2-5x longer than sodium lamps. This is a key reason LEDs are economically replacing sodium lamps worldwide. Statement 3: CORRECT. SODIUM LAMPS PRODUCE NEARLY MONOCHROMATIC YELLOW-ORANGE LIGHT centred at ~589 nm (sodium D-line emission). This narrow spectrum has very POOR colour rendering (CRI ~22 for LPS; ~25-65 for HPS), meaning colours look washed-out and hard to distinguish. LEDs can be engineered with broadband white spectra (warm white ~2700K, neutral white ~4000K, cool white ~5000-6500K) with CRI 70-90+, OFFERING SIGNIFICANT COLOUR ADVANTAGES — better visibility, traffic safety, and CCTV image quality for streetlights. So statements 1 and 3 are correct; 2 is reversed. Source: NCERT Class 12 Physics 'Wave Optics' / Bureau of Energy Efficiency (BEE) reports on UJALA / Street Lighting National Programme (SLNP).