The verdict is in: LED street lighting is better! Many cities including San Jose[1] and Oakland[2], CA, Portland[3], OR and others[4] have commissioned independent, third party studies that have all reached the same conclusion – LED street lighting meets or exceeds existing street lighting technologies in terms of the amount and quality of light while simultaneously consuming much less energy.
Here are five reasons why LED is better, the cocktail napkin for LED street lighting:
1. Improved Visibility for Motorists and Pedestrians
Typical nighttime locomotion occurs with lighting in the Mesopic range, so it is important that luminous flux (lumens) and illuminance (lux) values are properly adjusted for the Mesopic range. Huh? Okay, remember those rods and cones you learned about in seventh grade science? They operate best at the wavelengths in the Mesopic range where LED lighting shines (pun intended.)
When you move from a brightly lit room in your home to a room with the lights off, it takes several seconds for your eyes to adjust. This adjustment time can be hazardous when piloting a multi-ton vehicle at 35 mph or higher. And yet the High Pressure Sodium (HPS) roadway lighting prevalent today creates just such a situation as you drive from a very bright spot under an HPS light into a dark spot between lights. This poor uniformity, where the difference in brightness between the brightest and dimmest spots is high, causes the human eye to continually and dangerously adjust, with each adjustment taking seconds. A lighting layout with LED lights optimized for human rods and cones and better uniformity – the difference between the brightest and dimmest spots is low – dramatically improves safety.
To be sure, it is still possible to create a poor layout with LED lighting, which is much more directional. Focusing on very high light levels with large separation between poles, combined with the less diffuse lighting of LED, can create uniformity on par with HPS lighting – which is to say dangerous – so good lighting design is still a prerequisite.
BUGs also play a role here, though not the ones that sacrifice themselves on the altar of your windshield, reducing visibility, or ruining a peaceful nighttime walk with their itchy insurgence. The Illuminating Engineering Society (IES) defines a different kind of BUG, one that stands for Backlight, Up-light and Glare. LED lighting is directional, much more so than other lighting sources like HPS. As a result, it goes where intended. Much less is wasted to backlight, up-light or glare, improving motorist and pedestrian safety.
2. Reduced Energy Consumption
With an LED street lighting system, improved visibility for motorists and pedestrians requires less energy. I know, seems like some fundament law of nature is being violated here, but it’s a true win-win. The wattage needed per LED light to deliver more effective illumination as described above is less than the wattage needed per HPS light today, or other types of lighting as well (e.g., Low Pressure Sodium, Metal Hallide, Mercury Vapor.) Reduced wattage over time means reduced energy consumption and a lower carbon footprint.
3. More Accurate Color Representation
Color is an important ingredient when determining what something is from behind the steering wheel, like slippery anti-freeze on the road ahead or a deer just off the shoulder. If natural daylight provides a color representation of 100, HPS lights provide a color representation of about 25 while LED lights are typically over 70, much closer to natural daylight and much easier to identify potential hazards.
4. Meets the Latest Lighting Standards
Many, perhaps even most, street lighting systems today meet no lighting standards whatsoever or meet lighting standards that are way out of date. While stepping up to an LED street lighting system saves money and improves the quality of light, it’s also the perfect time to come into compliance with the latest standards like ANSI/IESNA’s RP-8-05[1] standard for roadway and adaptive street lighting and the International Commission on Illumination’s CIE-191:2010[2] standard for Mesopic Photometry. Doing so capitalizes on many years of research into the safest and most economical way to provide street lighting.
5. Leverages Adaptability
Huge strides have been made these past five years in lighting control technology allowing street lighting system owners to modify light output in response to environmental conditions like surrounding levels of activity levels, local motion, other nearby sources of lighting, etc. This is called adaptive lighting. Adaptive lighting not only reduces energy consumption further through the use of dimming, but also prevents over-lighting, reduces glare and minimizes light pollution. In other words, it helps deliver just the right amount of light when and where it’s needed most.
Gonzology 