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LED-Based Headlight Meets US Safety Requirements, Reduces Energy Consumption

Photonics Handbook
Researchers have designed an LED-based train headlight that uses one-tenth of the energy required for headlights that use conventional light sources. If operated eight hours every day, the electricity savings of the new design could reduce emissions of the greenhouse gas carbon dioxide by about 152 kg per year.

Researchers at National Taiwan University report a new train headlight design based on ten precisely positioned high-efficiency LEDs. The researchers combined the small outputs of multiple high-efficiency LEDs into a large circular output to create a beam large enough to meet or exceed U.S. federal regulations, which require that train headlights have a peak intensity of at least 200,000 cd and illuminate a person from at least 800 feet away.

LED-based train headlight, National Taiwan University.
A new train headlight design uses two half-circular parabolic aluminized reflectors with high-efficiency LEDs placed in the plane where the two reflectors come together. Courtesy of Wei-Lun Liang, National Taiwan University.

The researchers had to overlap the LED outputs enough to create a large beam, but not so much that more LEDs, and thus more energy, would be needed. To prevent circuit damage, the LEDs had to be placed far enough from each other for heat to dissipate.

Researchers used two half-circular parabolic aluminized reflectors to create the high-efficiency headlight. When used together, the strong beams from each reflector combine to generate the light intensity necessary to meet federal guidelines. This design also simplified placement of the circuits needed to power the LEDs because circuits could be housed in the horizontal divider separating the reflectors.

To determine where to place the LEDs in the reflectors, the researchers first estimated the best location of each LED and then used a series of tests and simulations to fine-tune the final position for each LED based on its corresponding illumination pattern.

LED-based train headlight, National Taiwan University.
Researchers designed a train headlight that uses two half-circular parabolic aluminized reflectors containing high-efficiency LEDs (a). The placement of each LED in the upper reflector is shown in (b). (c) shows illumination patterns corresponding to LEDs 1 to 5 arranged as in (b), demonstrating the individual and combined illumination areas from five LEDs in the upper reflector. When used together, the two reflectors form a circular illumination pattern. Courtesy of Wei-Lun Liang, National Taiwan University.

“Other scientists can use the linear equation we derived for deciding the approximate positions of LEDs for other applications,” said researcher Wei-Lun Liang. “This can substantially shorten the time required to determine LED positioning before fine-tuning the positions.” 

The researchers said that train headlights typically use a complete parabolic reflector surface.

“We believe this is the first design to use a combination of two semiparabolic reflector surfaces,” said Liang. “By systematically analyzing the design to determine the best placement of the LEDs in the reflector, we were able to minimize electricity consumption while satisfying requirements associated with traffic safety.”

“Some LED headlight products sold on the market are designed with many LEDs that have outputs that overlap in large sections. These designs waste a lot of energy,” said Liang. “Our research showed that electricity use can be reduced by focusing on the best way to distribute the LED energy equally."

The design uses a total of 20.18 W to accomplish the same light intensity as an incandescent or halogen lamp that uses several hundred watts. The new headlight can be dimmed by turning off some of the LEDs to avoid blinding waiting passengers when the train passes a platform, for example.

The researchers, who were approached by the engineering and design company Lab H2 Inc. to design locomotive headlights that use LEDs as a light source, are now working to turn their design into a commercial product. Even though the new design exhibits low power consumption, it still generates some waste heat. Before the design can be commercialized, the researchers plan to develop and test a heat dissipation system for the new headlight.

The research was published in Applied Optics, a publication of OSA, The Optical Society (doi: 10.1364/AO.57.001305).

Research & TechnologyeducationBusinessAsia-PacificLEDslight sourcesenergyautomotivetrain headlighttrain safetylensesparabolic surfaceTechnology News

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