Change can be hard. Witness the reluctance with which some building owners, and even consumers, are approaching the switch to certain lighting technologies, such as T8s and LEDs—even though these sources meet new energy mandates better than previous options.
For roadway lighting, change is already well under way in the form of solid-state lighting. The new paradigm gives designers and manufacturers immense opportunity to experiment with a light source that looks and behaves differently than conventional high-intensity discharge (HID) and high-pressure sodium (HPS) lamps. But rather than rush into unchartered luminaire design territory, many manufacturers have continued to stick with form factors that they are familiar with rather than exploring something new.
This lack of design change doesn't surprise John Bono, chairman of the IES Street and Area Lighting Committee. “Everyone's used to seeing cobra heads,” he says. “Everybody wants the same look except with LEDs [as the light source], but that doesn't necessarily allow LEDs to perform properly.”
Retired lighting engineer Del Armstrong, now president of Soft Lighting Systems in Bellevue, Wash., remembers seeing his first LED roadway fixture about six years ago. “It basically was LEDs mounted on a [metal] pan,” he says. “It didn't do that good of a streetlighting job.”
Though LED technology has advanced significantly since that demonstration, Armstrong still worries about the lack of considered optical design for LED streetlights. Whereas luminaires outfitted with conventional lamps need refractors to deliver candlepower to the roadway, LEDs, a point source, provide a more directional light than their filament-lamp counterparts. But to reduce glare and provide the contrast necessary for driver and pedestrian visibility, Armstrong would like to see fixtures in which the LEDs are aimed at about 60 degrees rather than the 72 degrees of HID or HPS luminaires.
Like many of his lighting colleagues, Armstrong would also prefer a lower spacing-to-mounting-height ratio than what many utility companies and municipalities anticipate in their quests to save costs by employing LEDs. Though LEDs generally have a better efficacy at cooler, brighter color temperatures, he finds 3000K to 3500K to be most successful in viewer comfort and reducing sky glow.
These optical requirements aside, Armstrong looks forward to seeing more design innovation in roadway LED luminaires. “We have a huge opportunity to do some really nice things with LEDs,” he says.
Several manufacturers, including the four discussed on the following pages, are starting to reimagine not only how the form of an LED roadway luminaire can speak to its function, but how its design can maximize the diode's potential as a source, while still producing quality illumination.
Manufacturers and designers have hit a few potholes on the road to LED conversion, but change is happening. And it looks promising.
Manufacturer: Kim Lighting
Overview: Altitude has an optical design created specifically for LEDs. Kim Lighting's patent-pending PicoPrism optics feature four LEDs and an acrylic prism in a replaceable, modular assembly. The LEDs, individually directed to provide horizontal spotlighting and redirect spill light, overlap to create uniform illumination. The horizontal spotlight is aimed at slightly less than 70 degrees.
Configurations: Altitude is available in six different housing sizes, from 23 ¼ inches by 17 inches in plan to 42 ¾ inches by 25 inches in plan; Altitude 180, 240, and 300 LED fixtures are most appropriate for roadway lighting.
Lighting Distribution: Available in nine IES distribution types, including one-way-left and one-way-right distributions
Height and Spacing: Altitude has a recommended mounting height of 10 to 40 feet and a spacing-to-mounting-height ratio (SHR) of 4 to 5.
Housing: Low-profile, composed of die-cast aluminum with a low copper alloy.
Thermal Management: Ribs, vents, and barrier walls separate electrical components from optics in the housing; ribbed exterior serves as the heat sink. A thermal sensor automatically lowers the current when ambient temperature becomes too warm.
Color Temperature Options: 4000K, 5000K, and amber
- Rotatable photoelectric receptacle.
- Wireless control optional.
- Retrofit with existing poles possible.
- Neighbor-friendly optic option (similar to IDA compliant) further reduces backlight.