Orange street lights are a specific type of high pressure sodium (HPS) lamp used for street lighting. HPS lamps produce a distinct orange glow that makes them easily recognizable. There are a few key reasons why orange HPS street lights are so commonly used:
Energy Efficiency
HPS lamps are among the most energy efficient options for street lighting. They can convert up to 45% of the electrical input power into visible light, compared to only about 15-25% for standard incandescent bulbs. This improved efficiency leads to lower energy usage and cost savings.
Long Lifespan
The typical lifespan of a HPS lamp is 24,000 hours or more. This is 3-4 times longer than older lighting technologies. The longer lifespan reduces the frequency of costly lamp replacements.
Good Color Rendering
While HPS lights skew to the red/orange end of the visible spectrum, they still provide reasonably good color rendering of 80-85 on the CRI (color rendering index) scale. This allows people to see clearly under HPS lighting. The orange hue also cuts through fog/haze better than bluer light sources.
How HPS Lights Produce Orange Light
High pressure sodium lamps work by generating an electrical discharge between two electrodes in an arc tube filled with xenon gas and sodium metal vapor. The high pressure xenon gas allows the lamp to start quickly. Once the sodium vaporizes, it dominates the color emitted.
Atomic Emissions
When sodium atoms are excited by the electrical current, they emit light at specific wavelengths as they return to lower energy states. The most prominent emissions are at 589 nm and 589.6 nm, corresponding to orange-yellow light. This gives HPS lamps their distinctive monochromatic orange hue.
High Pressure Effects
Operating the sodium vapor at high pressures broadens and shifts the emitted spectral lines. This improves color rendering by filling in the gaps between the narrow sodium emissions. The high pressure also raises the lamp’s luminosity by enabling more electric current to flow through the plasma arc.
Types of Orange HPS Street Lights
There are a few different kinds of HPS street lights that all produce orange light. The main variables are lamp power, fixture design, and light distribution.
Common Wattages
| Wattage | Use Cases |
|---|---|
| 50W | Residential streets, low-traffic areas |
| 70W | Collector roads, medium pedestrian traffic |
| 100W | Major roads, higher traffic and visibility needs |
| 150W | Highways, interchanges, high-visibility areas |
Higher wattages are used where more light output is needed. The lamp’s luminous efficacy also increases slightly at higher power levels.
Cobra Head Street Lights
Cobra head fixtures are designed to distribute light efficiently over a large area. They contain reflectors to direct HPS lamp light downwards and side panels that prevent light trespass. The name comes from the shape resembling a cobra’s head.
Decorative Street Lights
Decorative HPS fixtures have an ornamental appearance for historical districts and pedestrian zones. But they still provide ample illumination of sidewalks and streets using internal reflectors. Glass panes also help control optical distribution.
Comparisons to LED Street Lights
Many cities today are switching street lights from HPS to more energy efficient LEDs. But orange HPS lights still have advantages in certain situations.
HPS Strengths
– Lower upfront costs
– Proven reliability in extreme conditions
– Better cold weather performance
– Broad light distribution from omni-directional sources
LED Strengths
– Much higher luminous efficacy (more light per watt)
– Long lifespan of 50,000+ hours
– Instant on/off and dimming capabilities
– Directional optics for precise lighting control
Light Color Differences
| Light Source | Color Temperature | Appearance |
|---|---|---|
| HPS | 2100K | Orange/amber tones |
| LED | 3000-4000K | Neutral or cool white |
LEDs can also be tuned to various color temperatures, while HPS lamps emit nearly monochromatic orange light. Some cities use filter coatings on LEDs to mimic the HPS orange color.
Future Outlook
LED lighting is rapidly taking over the street lighting market due to energy savings and smart control capabilities. But HPS lamps will still occupy many roadway fixtures for years to come. Their low cost and proven performance ensure they will remain the orange glow of street lighting infrastructure. As LED technology continues improving, we will eventually see the orange mantle passed from HPS to warmer color temperature LEDs.
Conclusion
Orange street lights are high pressure sodium lamps valued for their long life, energy efficiency, and cost-effectiveness. Their distinctive color comes from atomic emissions of excited sodium vapor under high pressure conditions. HPS will remain popular for street lighting, though LEDs are displacing them in many cities. The monochromatic orange glow of HPS has become an iconic part of nighttime urban and suburban environments.
