Street Lighting Comparison: LED vs. HPS
Introduced circa 1970, High-Pressure Sodium (HPS) lights have remained a popular street lighting solution. Despite their widespread usage, however, HPS lamps display numerous deficiencies, particularly when compared with newer lighting technologies.
HPS streetlights gained widespread acceptance solely for this reason: They generate the greatest amount of photopic illumination (visibility in well-lit environments) while minimizing power consumption. Unfortunately, when it comes to visibility, HPS solutions still fall woefully short in comparisons with white light sources. The latter has been shown to double driver peripheral vision and increase brake reaction time by 25%.
HPS visibility issues are compounded by its inherent color limitations. High-Pressure Sodium lamps generate narrow spectrum light, which appears to us as a dull yellow glow. Hampered by an extremely low Color Rendering Index, these lights simply cannot accurately reproduce colors.
On a more positive note, many new lighting technologies maximize energy-saving light bulbs while significantly outperforming HPS lighting in the areas of visibility and color precision. Among the most promising of these innovative solutions are high-quality LED street lights. The differences between LED and HPS illumination are striking.
LED lamps with a color temperature of 3.500-4.200 K generate significantly more natural white light than do yellow HPS lamps. The more natural ‘daylight’ spread far and wide by LEDs in turn creates greater visibility and safer conditions for both motorists and pedestrians.
An adjunct to superior LED visibility is their color accuracy. LEDs rank extremely high in this area, having a Color Rendering Index (80-90). Unlike HPS lamps, they consistently display the natural colors of an illuminated environment.
While LEDs offer excellent visibility and color accuracy, they lose nothing when it comes to energy efficiency. In fact, they significantly outperform HPS lamps in this category. When comparing the two, energy-saving light bulbs consume 40-80% less electricity than do standard HPS lamps.
In terms of actual wattage, a 30W LED lamp approximates the light output of a 80W HPS. This feat of efficiency stems from the directionality of LEDs, which focus light downwards and spreads illumination evenly over a given area. As a result, one LED lamp requires significantly less wattage than does an HPS to illuminate the same area.
Thanks to their noteworthy efficiency, LEDs burn about five times as long as HPS street lights (about 100,000 hours). Longevity, of course, means fewer new bulbs must be purchased, and fewer labor hours will be charged to do the replacing.
Having to replace bulbs more frequently isn’t even the most concerning part of their longevity, however, as well before a High-Pressure Sodium street light runs its course it begins to falter. During its lifespan, an HPS will experience lumen depreciation (loss of brightness) much earlier (about six months) and more quickly than will an LED of comparable light output. With visibility already compromised by HPS illumination, this rapid drop-off only makes a bad situation worse.
This comparison clearly demonstrates the inherent advantages of LEDs when pitted against much older HPS technologies. For those interested in optimum efficiency and performance in contemporary street lighting, LEDs offer a very encouraging alternative to older solutions.