A new train headlight design uses two half-circular parabolic, or cup-shaped, aluminized reflectors with high-efficiency LEDs placed in the plane where the two reflectors come together. Combining the strong beams from each reflector generates the light intensity necessary to meet safety guidelines. Credit: Wei-Lun Liang, National Taiwan University

A team of researchers has developed a new LED-based train headlight that uses a tenth of the energy required for headlights that use conventional light sources, resulting in significant cost savings.

If the new headlights are installed and operated for eight hours daily, owners would see a reduction of about 152 kilograms of carbon dioxide emissions per year.

Train headlights must be visible from a distance far enough away to give people or vehicles enough time to move out of the way. Traditional train headlights use incandescent or halogen bulbs that are bright enough to meet safety regulations. However, they are not very energy efficient because most of the energy powering the light is converted into heat rather than visible light.

“Some LED headlight products sold on the market are designed with many LEDs that have outputs that overlap in large sections,” Wei-Lun Liang, of the Micro Optics Device Laboratory, said in a statement. “These designs waste a lot of energy.

“Our research showed that electricity use can be reduced by focusing on the best way to distribute the LED energy equally,” he added.

The new train headlight design is based on 10 precisely positioned high efficiency LEDs, using a total of 20.18 Watts to accomplish the same light intensity as an incandescent or halogen lamp that uses several hundred watts. The new headlight can also be dimmed by turning off some of the LEDs to avoid blinding waiting passengers when the train passes by a platform.

“Combining several LEDs is more expensive and consumes more electricity than using a few single LEDs,” Liang said. “Thus, we needed to determine how to best position the lowest possible number of high--efficiency LEDs needed to meet the requirements by analyzing how the parabolic surface reflected the LED lights.”

U.S. federal regulations require train headlights to have a peak intensity of at least 200,000 candelas and illuminate a person at least 800 feet in front of the headlight. This forced the researchers to overlap the LED outputs just enough to create a large beam but not so much that more LEDs and more energy would be needed. The LEDs must also be placed far enough from each other for the heat to dissipate to prevent circuit damage.

The researchers used two half-circular parabolic aluminized reflectors to position the LEDs to create a high-efficiency train 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 they could be housed in the horizontal divider separating 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.

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

The researchers are now focusing on converting the design into a commercial product by developing and testing a heat dissipation system.

The study was published in Applied Optics.