Powerful LED-based train headlight optimized for energy savings

February 13, 2018, Optical Society of America
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

Researchers have designed a new LED-based train headlight that uses a tenth of the energy required for headlights using conventional light sources. If operated 8 hours every day, the electricity savings of the new design would reduce emissions of the greenhouse gas carbon dioxide by about 152 kilograms per year.

Train headlights not only illuminate the tracks ahead, they also play an important role in rail transportation. Because trains are difficult to stop, the headlights must be visible from a distance far enough away to give people or vehicles on the tracks ample time to move out of the way. Traditional train headlights, which use incandescent or halogen bulbs, are bright enough to meet safety regulations but are not very efficient because most of the energy powering the light is converted into heat rather than visible light.

Researchers led by Guo-Dung J. Su from the Micro Optics Device Laboratory of the Graduate Institute of Photonics and Optoelectronics at National Taiwan University, Taiwan, were approached by the engineering and company Lab H2 Inc., to design locomotive headlights that use LEDs as a light source. In addition to requiring less energy, LEDs also last longer and are smaller and more rugged than traditional light sources.

"Some LED 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 Wei-Lun Liang of the Micro Optics Device Laboratory, who was instrumental in designing the new train headlight. "Our research showed that electricity use can be reduced by focusing on the best way to distribute the LED energy equally."

In The Optical Society journal Applied Optics, Liang and Su report a new train headlight design based on ten precisely positioned high efficiency LEDs. The design uses 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 a platform, for example.

Designing for energy efficiency

Much like those used for cars, train headlights typically combine a light source with a parabolic, or cup-shaped, reflective surface that focuses the emitted light into a beam. Although LEDs are a great option for saving energy, the most energy-efficient LEDs emit smaller spots of light. For this reason, the researchers had to combine the small outputs of multiple high-efficiency LEDs into a larger circular output to create a beam large enough to use as a train headlight.

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. Credit: Wei-Lun Liang, National Taiwan University
"Combining several LEDs is more expensive and consumes more electricity than using a few single LEDs," said Liang. "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."

The researchers' goal was a headlight that would provide light 1.25 times the brightness required by U.S. federal regulations. These 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.

Positioning the LEDs to save energy and meet federal guidelines came with several challenges. The researchers had to be careful to overlap the LED outputs just enough to create a large beam, but not so much that more LEDs, and thus more energy, would be needed. Also, the LEDs must be placed far enough from each other for heat to dissipate to prevent circuit damage.

Positioning the LEDSTo create a high-efficiency train headlight, the researchers used two half-circular parabolic aluminized reflectors. When used together, the strong beams from each reflector combine to generate the 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.

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. "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 point out that headlights typically use a complete parabolic reflector surface. "We believe this is the first design to use a combination of two semi-parabolic 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."

The researchers 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 will need to develop and test a heat dissipation system for the new headlight.

Explore further: Realizing highly efficient quantum dot LEDs with metallic nanostructures at low cost

More information: Wei-Lun Liang et al, Design of a high-efficiency train headlamp with low power consumption using dual half-parabolic aluminized reflectors, Applied Optics (2018). DOI: 10.1364/AO.57.001305

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not rated yet Feb 13, 2018
Does this still run hot enough to melt snow & ice off the front ? IIRC, the Japanese introduction of LED traffic lights was delayed by having to retrofit heaters...
not rated yet Feb 13, 2018
If this can be adapted for grow-ops...
not rated yet Feb 13, 2018
Does this still run hot enough to melt snow & ice off the front ? IIRC, the Japanese introduction of LED traffic lights was delayed by having to retrofit heaters...

Really depends on the LED's used. I have a flashlight with 7x XML2-T6 LED's and these things can get very very hot, they only use about 19w-22w @ 3.7v-4.2v They are incredibly powerful as well.
Thorium Boy
not rated yet Feb 14, 2018
Trucks and larger cars that sport these super bright LED headlights are a menance, able to dazzle oncoming drivers the way accidentally leaving highbeams on can, even from behind, into the driver's mirror. They should be banned. No one needs blazing head lights in normal urban driving.
5 / 5 (1) Feb 14, 2018
I have a flashlight with 7x XML2-T6 LED's and these things can get very very hot

If a LED light gets hot like that, it's poorly designed. LEDs don't tolerate high ambient temperatures, and start to lose performance and age fast above 50C. If the housing for the light is hot to the touch, the LED inside is even hotter.

That's a problem with many LED products, especially those designed to fit standard sockets, because the body of the lamp can still heat up to 80 C and above, and that kills the LED sooner or later. That's why they don't recommend installing them in recessed cans or other enclosed spaces.

The absolute efficiency of a LED is still actually very poor, on the order of 25% which means 75% of the input power is still going to heat. The trouble is, if the junction inside the diode heats up to 125 C or above, it gets destroyed, and the thermal connection from the tiny junction to the outside is quite poor.
5 / 5 (1) Feb 16, 2018
This design belongs into obsolescence management.

Hardly. There's nothing wrong with the edison socket or similiar. All the other alternatives have failed to make ground because of their contrived designs, fragile parts, cost, etc.

It's not the socket that is the problem, but the LEDs and their auxillary components. For example, solid state capacitors exist with lifespan of 100,000 hours at 105 degrees C. They're not used because they cost more, and the factories churning out lightbulbs want to push the manufacturing costs closer to 50 cents than $5 per bulb.

The EM noise out of a properly regulated LED bulb is also neglible. Again, cost is an issue, and manufacturers often just let the LEDs themselves do the rectifying with a simple current limiter in line, which results in lights that strobe - but hey, got to meet that $3 price point somehow.

LEDs will become better over time, but currently there's no incentive to improve since the competition was oulawed.

5 / 5 (1) Feb 16, 2018
In the end, it doesn't matter if the LED bulbs only last for a year as long as you can buy a pack of 10 for just a couple bucks, like you used to with standard bulbs.

The issue is that they outlawed standard bulbs because they were getting too cheap to make by just about anyone, so there was no longer a profit margin to speak of. Phillips et al. introduced and lobbied the lightbulb bans to make themselves elbow room on the market against competition by introducing artifical complications that the competitors weren't prepared for.

And as the CFL bulbs were a resolute failure hated by just about everyone, there are now no real alternatives to LED lighting, for better or worse.
not rated yet Feb 19, 2018
One of problems is, the heat sensitive components are placed inside this socket above the source of heat. This socket is perfect except it was designed for incandescent lamps before hundred years - not LED or fluorescent ones.

One of the most heat sensitive component, and the one that's actually producing most of the heat, is the LED itself, that cannot be placed anywhere else for obvious reasons. The rest can be made to handle the heat, cost permitting.

No socket by itself can really do away with the heat problem as long as the whole business has to be integrated into the bulb itself, and moving the other components out of the socket to a separate ballast introduces just more complication and more cost to the consumer because of the different requirements of different LEDs.

For example, you could make a current limited DC bus in your house to drive a bunch of bare diodes, but then those diodes must be of a specific type to work with that particular system

not rated yet Feb 19, 2018
So it's no longer a question of, buy a bulb, screw it in, flip the light switch.

You'd actually need two sockets per light, one to house the actual light and the other to house the ballast for that light. If you buy a system now, and the bulbs last ten years, then ten years down the line when you buy a brand spanking new bulb you also need to overhaul the ballast system to match your new bulb.

Then you'd get problems of people fitting new bulbs with old ballasts, or new ballasts with old bulbs, so to combat that issue they'd have to make the sockets incompatible across generations... which by business practicalities becomes incompatibility across different manufacturers(!), so you'd be married with Phillips instead of Osram and vice versa.

That's another reason why the standard screw socket is a nice thing to have.
not rated yet Feb 19, 2018
Or, if you go for a really techy solution, you could imprint each LED with a standard chip which communicates with the power supply over data lines, and tells it exactly how much current and voltage it requires, what sort of dimming is permitted, how hot it is running, etc.

But then you need a whole computer system with network cabling running through your house just to keep the lights on, and that has the problem of all built-in home automation systems: cost, maintenance, management and obsolescence, planned or otherwise.

Meanwhile, you can still buy an old antique desk lamp that you like, and screw in a new bulb, and it just works. There's no questions about whether the lamp and the bulb speak the same digital protocol, or worries about hackers getting into your IoT light switch and burning down the house.

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