New LED streetlight design curbs light pollution

April 24, 2013, Optical Society of America
This photograph (left) illustrates some of the shortcomings of a traditional streetlight: light pollution, glare, wasted energy, and an uneven illumination of the ground. The perfect design for a streetlight (far right) would eliminate these problems. Credit: Optics Express.

Streetlights illuminate the night, shining upon roadways and sidewalks across the world, but these ubiquitous elements of the urban environment are notoriously inefficient and major contributors to light pollution that washes out the night sky. Recent innovations in light emitting diodes (LEDs) have improved the energy efficiency of streetlights, but, until now, their glow still wastefully radiated beyond the intended area. A team of researchers from Taiwan and Mexico has developed a new lighting system design that harnesses high-efficiency LEDs and ensures they shine only where they're needed, sparing surrounding homes and the evening sky from unwanted illumination. The team reported their findings today in the Optical Society's (OSA) open-access journal Optics Express.

A unique feature of the new LED system is its to different street lamp layouts, "to all kinds of streets and roads, providing a uniform illumination with high ," says co-author Ching-Cherng Sun of National Central University in Taiwan. For example, some modern lamps that line a thoroughfare or suburban sidewalk lean into the middle of the road, lighting the street from above. But more often, lamps are posted to one side of a street, or alternating in a "zig-zag" pattern from one side to the other – a layout that may be more efficient for roads with high . The new design provides flexibility to be used for different illumination requests while maintaining a , Sun says.

The proposed lamp is based on a novel three-part lighting fixture. The first part contains a cluster of LEDs, each of which is fitted with a special lens, called a Total Internal Reflection (TIR) lens, that focuses the light so the rays are parallel to one another instead of intersecting—a process called collimation. These lens-covered LEDs are mounted inside a reflecting cavity, which "recycles" the light and ensures that as much of it as possible is used to illuminate the target. Finally, as the light leaves the lamp it passes through a diffuser or filter that cuts down on unwanted glare. The combination of collimation and filtering also allows researchers to control the beam's shape: the present design yields a rectangular light pattern ideally suited for street lighting, the researchers say.

This is an example of the new design's adaptability: If an LED street lamp projected its light from the center of the street, the light pattern on the road would be a rectangle. If the lamp stands on the side of road, it projects its light at an angle, producing a trapezoidal light pattern. The new design includes alternative configurations that would maintain the light beam's rectangular shape for a lamp that must project its beam at an angle, ensuring an even illumination of the road. Credit: Optics Express.

The team tested their design's performance by analyzing how little the beam would spread as it hit its target—a road or sidewalk 10 meters or more away from the source of the light. They quantified the lamp's performance using something called optical utilization factor (OUF), a number that describes the relationship between the flow rate of light at the target and the flow rate of light coming directly out of the . Higher OUF indicates better performance. Simulations show that the new design achieves an OUF of 51 to 81 percent, greatly outperforming a recent "excellent" design that reached 45 percent. Furthermore, the proposed streetlamp meets high expectations for power and brightness. And is also significantly reduced: for conventional street lamps, up to a fifth of their total energy is directed horizontally or upward into the sky. The best LED streetlamps reduce this to a tenth of their total energy. In the new model, just 2 percent of the lamp's total energy would contribute to light pollution.

New LED streetlight design curbs light pollution
This is a schematic of the new street lamp. Credit: Optics Express.

In addition to cutting light pollution and glare, the new model could also save energy. "A general LED street could reduce power consumption by 40 to 60 percent," Sun says; the increased efficiency of the proposed design would likely save an additional 10 to 50 percent. Furthermore, he adds, the module would be simple to fabricate, since it comprises just four parts, including a type of LED bulb commonly used in the lighting industry.

Sun's team expects to finish a prototype of their design in the next 3 to 6 months, and to begin practical installations of the new street lamp as early as next year.

Explore further: Low-energy LED lighting project is streets ahead

More information: "High-performance LED street lighting using microlens arrays," H. Lee et al., Optics Express, Vol. 21, Issue 9, pp. 10612-10621 (2013) … fm?uri=oe-21-9-10612

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1 / 5 (2) Apr 24, 2013
"A team of researchers from Taiwan and Mexico has developed a new lighting system"

Nope, they simply found out about LED projectors. Same tech will be used soon in almost every car (Audi is already using this technology - less energy consumption, better road safety).

Even not a pro that is interested in very powerful LED lamps that include optics know how this works.
1 / 5 (1) Apr 24, 2013
Nope, they simply found out about LED projectors

Nope, they simply found out about Blender 3D Modelling and Animation software.
5 / 5 (1) Apr 25, 2013
But lights that illuminate the surrounding environment allows you to spot and anticipate threats like a pedestrian that are going to cross the road. With these new lights you see the danger only when it's already on the road and then it might be too late to avoid an accident.
3 / 5 (2) Apr 25, 2013
But lights that illuminate the surrounding environment allows you to spot and anticipate threats like a pedestrian that are going to cross the road.

Sidewalks will be included (you think they'll turn sidewalks into no-light zones?).

People "haphazardly crossing the road out of unlighted patches in non-sidewalk areas" aren't a frequent occurence. And you still DO have your headlights for you to see them (and them to see you).
1 / 5 (1) Apr 25, 2013
Imagine being able to see, I mean REALLY see the sky in cities. I took me forever to realize that the Milky Way that we are supposed to be able to see is only visible in the southern Hemisphere or along the northern hemisphere horizon... not visible in a cit. Going to the Canadian wilderness didn't give me much more than i could see at home.

But cities would have to make a concerted effort... they would basically have to want to install these systems for this reason. But imagine Denver with 80% of light pollution gone.. it's low humidity gives it super clear nights.

Only downside I can see would be for pilots making night landings... yes the airport would be lit up like nothing else ... but the cities you are used to looking down on would go dark.
not rated yet Apr 25, 2013
Simple Reason why Not Even Street Lights are Public Goods - Turn them all off.

1 / 5 (1) Apr 27, 2013
For the first time ever, I agree with vendicar.E - turn them all off.

Enhance your personal security with more firearms.
5 / 5 (1) Apr 27, 2013
People "haphazardly crossing the road out of unlighted patches in non-sidewalk areas" aren't a frequent occurence. And you still DO have your headlights for you to see them (and them to see you).

You forget animals and hitchhikers, and drunks. Your headlights on low beam won't show things as far away as streetlights would, so your reaction time is significantly shortened. Otherwise, why bother with street lights in the first place? (Driving around on high beams just makes you a dick.)

Anyways, the point of street lighting is to let you see the unexpected before it becomes the unfortunate. That presumes the events are somewhat rare.
1 / 5 (1) Apr 29, 2013
I totally disagree ...

on streets lighting is always for pedestrians and vehicles get the added convienece of more light. Street light have been around LONG before motor vehicles -- they outline the street and are for the people walking, to feel safer in cities.... country roads tend to be unlit as very few people walk them.

Lighting on highways and interstates of course are only for vehicles... but on the street where pedestrians are common the light is theirs and cars get a benefit as well.

remember Edison's gas lamp with a light bulb ... gas lamps are street lights... like San deigo's gas lamp district
1 / 5 (1) Apr 29, 2013
You forget animals and hitchhikers, and drunks.

Hitchikers crossing the road without looking? Where do you live?

As for drunks and animals: Again - where do you live? Animals in regions with sidewalks?

And if you're driving the countryside - which usually doesn't havy any type of road lighting at all- then why aren't you using your high beams? Afraid of blinding all those millions of drunks and hitchhikers?
5 / 5 (1) May 09, 2013
Animals in regions with sidewalks?

You don't drive much do you? There's foxes and badgers and dogs and cats and whatever all over the cities and suburbs. Then there's the smaller towns that aren't really urban but not countryside either, where you got streetlights, but no sidewalks because it's basically in the middle of a forest or field, and you still got people walking the road, and you also get larger animals like deer or moose.

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