Energy Efficiency
HPS sodium lights: 80–130 lm/W efficacy (but much of the light is wasted upward and sideways in omnidirectional fixtures). Effective road delivery: 50–70 lm/W. LED street lights: 130–160 lm/W efficacy, directional optics deliver 90%+ to the road. Effective road delivery: 120–145 lm/W. Conclusion: an LED delivers 2× more road light per watt of electricity. A 100W LED replaces a 250W sodium light with the same or better road lux level.
Light Quality and Visibility
Sodium lights emit yellow-orange light at ~2100K with CRI <25. This means colours are severely distorted - all objects appear in shades of yellow. Red cars look dark, people's faces are unnatural, road markings are harder to distinguish. LEDs at 5000–6500K with CRI 70+ render colours naturally, improve contrast, and significantly enhance peripheral vision for drivers. Multiple studies show 15–30% fewer nighttime accidents after LED conversion. Emergency services and CCTV cameras also perform far better under LED light.
Lifespan and Maintenance
HPS lamp rated life: 15,000–24,000 hours. After 12,000 hours, a sodium lamp retains only 70% output but consumes the same wattage - you are paying full electricity for declining light. Lamp replacement needed every 3–4 years. LED rated life: 50,000 hours (L70). Maintains output well for 15+ years at 8 hours/day. No lamp replacement needed. In a city with 10,000 street lights: sodium maintenance (lamp replacement + labour) costs ₹1–2 crore every 3 years. LED maintenance over 10 years: essentially just cleaning - saving ₹3–6 crore over 10 years.
Upfront Cost and Payback
A 100W LED street light replacement for a 250W sodium light: LED fixture cost: ₹4,000–₹8,000. Energy saving: 150W × 10h × 365 days = 547.5 units/year. At ₹7/unit: ₹3,832.50 saved per year per light. Payback: 1–2 years. For 10,000 streetlights: annual energy saving after conversion = ₹3.83 crore. Conversion project cost: ₹5–8 crore. Payback: 1.5–2 years. Then pure savings for the remaining 10–15 years of LED life.
