HPS vs LED Streetlights
-- Efficacy, Lifespan, and the Off-Grid Math
HPS vs LED Streetlights: Efficacy, Lifespan, and the Off-Grid Math
Short answer: LED wins on every number that matters — efficacy, lifespan, color rendering, and dimming — and the gap is wider off-grid than on-grid. HPS (High-Pressure Sodium) lamps produce light by exciting sodium vapor; LEDs produce it by electron–hole recombination in a semiconductor PN junction. That difference in physics is why an HPS fixture needs 30–50% more energy for the same light output, and why we have not specced HPS on a solar product in years.
HPS vs LED at a glance
| Parameter | HPS | LED |
|---|---|---|
| Luminous efficacy | 50–100 lm/W | 100–200 lm/W |
| Color rendering (CRI) | 20–40 — serious color distortion | 70–90+ — accurate color |
| Lamp lifespan | 10,000–20,000 hours | 50,000–100,000 theoretical; 30,000–50,000 real-world |
| Energy for same output | 30–50% more than LED | 50–70% of HPS consumption |
| Dimming | Poor — efficacy drops when dimmed | Native — dimming is standard practice |
| Cold-weather start | Long startup and restrike times | Instant at temperature |
CRI (Color Rendering Index) scores how faithfully a light source reveals object colors on a 0–100 scale. HPS sits at 20–40, which is why faces and cars look washed-out yellow under sodium light. LED at 70–90+ renders colors accurately enough for drivers to read plates and spot hazards.
Why the gap gets bigger off-grid
On a grid-connected street, a 30–50% energy penalty shows up on a utility bill. On a solar street light it shows up in the battery and panel budget. The arithmetic we run on every project: the same road lighting job done with HPS draws roughly twice the daily energy of the LED version, so the battery bank and the panel both roughly double to carry it. Add HPS's inability to dim — an LED fixture drops to 30% output after midnight and saves the difference — and the off-grid case stops being close.
HPS also carries components LEDs simply do not have: filaments and electrodes that age, and ballasts that fail frequently. Each failure is a service call with a trained technician, and lamp-plus-ballast-plus-transformer replacement keeps the lifetime cost high even where the fixture price looked attractive.
What LED brings — and where it fails
The LED side of the ledger: electron–hole recombination in the PN junction converts electrical energy to light with high efficiency and minimal loss, which is where the 100–200 lm/W comes from. The solid-state structure has no filament to burn out, real-world service life lands at 30,000–50,000 hours, and intelligent dimming stacks further savings on top. Smart monitoring catches drifting drivers before the road goes dark, and routine maintenance shrinks to cleaning and basic inspection.
One honest caveat, because the "LED never fails" pitch is oversold: the LED emitters themselves are rarely the problem. The driver is the component that fails in the field. We see driver failures far more often than emitter failures, usually after water ingress or after years of thermal cycling. When we compare quotes, we look at the driver's protection rating and its track record, not the emitter's advertised lifetime.
What this comparison does not cover
This page compares lamp technologies for street lighting. It does not cover pole and foundation design, wind-load structural calculations (see our wind load calculator), or controller selection — for charge-controller choice on a solar fixture, see our MPPT vs PWM guide. For complete fixtures with the LED engine, driver, and optics already matched, see our all-in-one solar street lights line.