LED technology has been making steady progress in the traffic industry for years. Now with the addition of solar power, LED's popularity can only increase...
The advantages of LED (light emitting diode) technology have been proved with the widespread use of LED traffic signals. Energy savings of 90%, a maintenance interval extended by at least 500%, and lower accident risk due to reduced signal failure have made LED traffic signals standard technology in many regions.
Two new LED technologies have the ptential for a similar market penetration: solar-powered LEDs and LED edge-lit signage. Both offer opportunities to improve transport safety and service through better lighting at reduced cost.
The primary domain of solar-powered lighting has historically been remote locations, particularly marine environments. Now, the integration of LEDs has so greatly increased the capabilities and cost-effectiveness of solar power that the sun can be efficiently used virtually anywhere, even in urban settings.
Integrated solar-powered LED lighting has the advantage of costing as little as one tenth as much as conventional hardwired lighting to install, because there is no digging or trenching, no cabling no power connection permits to acquire and no traffic disruption.
Plus, like LED traffic signals, solar-powered LEDs save significantly in operational costs by not requiring bulb repllacements or other routine maintenance - LEDs last up to 100,000 hours. Solar LED lights are rated to operate maintenance-free for a minimum of five years.
Whereas LEDs in traffic signals have facilitated the installation of battery backup for blackouts (California Sacramento County invested $500,000 in one such system), solar power requires no backup. In fact, there are no electrical costs and no added burden on the power grid. For these reasons, self-contained solar-powered LED lighting systems typically pay for themselves withing the first year.
First perfected for use in marine navigation in the late 1990's, solar LED technology was engineered to perform in the harshest environments on earh, rated for temperatures from -40°C (-40°F) to +80°C (176°F) at latitueds of up to 60° north. Nearly industructible and highly vandal resistant, solar LEDs can be installed virtually anywhere.
Self-contained solar-powered systems are now used for public transit lighting for bus stops and shelters, pedestrian beacons and programmable school-zone flashers, and a variety of roadway signaling options, such as 24-hour flashing beacons for sign enhancement.
Solar-powered bus stop and bus shelter lighting systems are an affordable and effective way to upgrade transit services and improve rider satisfaction and safety. Bus stops can incorporate up to three types of solar-powered LED lighting:
- Security downlighting to illuminate the waiting area to approximately a six-foot radius;
- Edge-lit bus schedule illumination, activated on demand for 30- to 60-second intervals;
- Passenger-activated signaling for bus drivers.
With 1 mile (1.6km) nighttime visibility, this bus flagging capability improves ontime efficiency and is particularly valuable for areas with poor street lighting and/or high driving speeds, giving drivers more time to safely slow down and reducing pass-bys - the number one complaint reported by some transit agencies. Modularity enables installation of any or all of these features in stages, and components are easily replaced. Solar-powered lighting kits are also available for new or existing bus shelters. All-night, low-level light reduces loitering and vandalism, while transit riders can increase light level on demand.
The City of London, England, has been a pioneer in the development of solar-powered bus stops and shelters, extensively evaluating their performance since 2001. The city authorities predict that solar-powered bus shelters will cost 36 per cent less overall than conventionally powered shelters.
In North America, over 75 transit agencies have installed solar-powered bus stops or shelters, most recently Toronto (150 units) and Los Angeles (300 units).
Pedestrian and School Zone
Solar-powered pedestrian beacons integrate the latest solar LED technology into pushbutton-activated crosswalk warning beacons. The trenching, cabling and disruption to traffic flow traditionally required to connect multiple beacons in a system is avoided by using frequency hopping spread spectrum technology to provide a wireless link - no control cabinet required. A flexible design enables any configuration of bi-directional or vertical/horizontal dual flasher solutions. The Manual on Uniform Traffic Control Devices (MUTCD) standard 12 inch yellow LED lenses are visible for up to 0.5 miles (0.8 km) during the day and 7 miles (11 km) at night. Battery packs, integrated into the solar charging unit, are replaceable to extend the life of the unit beyond the five-year maintenancefree interval.
Identical technology is applied to 24-hour flashing beacons and programmable school-zone flashers. Additionally, up to one year of dateltime operation settings for the school-zone flasher can be pre-programmed on a computer using an intuitive Windows-based graphical user interface, then easily transferred to the beacon through a wireless link. Programs can be easily copied for reuse at other schools. The unit can also operate as a regular crosswalk beacon when not in 'auto flash' mode.
Another new application of LED lighting for roadways also dramatically reduces energy, installation and maintenance costs. LED edge-lit signage is now available for street name signs and traffic control signs, including new stop signs that meet MUTCD specifications.
Edge-lit technology has been used in commercial and architectural signage for several years and is well suited for traffic applications. Light is emitted in a plane parallel to the sign face from LEDs embedded in the sign edge and refracted outwards through the sign material. The latest ultra-bright LEDs and advanced illumination technology provide exceptionally crisp, uniform illumination of the entire sign surface.
One advantage is narrow construction. Single-sided or double-sided signs are less than two inches thick, including the built-in power supply. Single-sided signs can be attached directly to a traffic signal mast arm - like reflective signs eliminating any moving parts and maximizing overheight clearances. Doublesided edge-lit signs can be installed using the same hardware as fluorescent signs.
LEDs provide maintenance intervals 10 times that of the fluorescent tubes traditionally used in illuminated signs. White LEDs currently have a lifespan of 50,000 hours, with a mean time between failure far beyond this, so expensive, unscheduled maintenance calls are very seldom required. Unlike fluorescent tubes, they also perform well in hot and cold climates. Additionally, LED edge-lit illumination is extremely energy efficient, about 90 per cent better than fluorescents, and may qualify for energy grants. A six foot, single-sided sign can require as little as 15 watts, versus 192 watts for a typical fluorescent or about 88 watts for an LED retrofit.
LED edge-lit signs can be constructed with transparent retro-reflective sheeting on the outer panel, so that in the event of a power failure, the sign will retain retroreflectivity. As with LED traffic signals, low wattage also facilitates the option of battery backup.
Given the vast improvements in maintenance intervals, energy consumption, capital costs and ease of installation, LED edge-lit illuminated signs and integrated solar-powered LED lighting are poised to become standard hardware for roadway and transit illumination.
The author would like to thank Tim Shuff and Harbourwerks Strategies for their research and assistance.