Lasers are more efficient and offer a more natural white light
I am standing in a twilit underground lab looking at the most powerful car headlight in the world. Its source, a blue-laser diode, is 1000 times as bright as an LED but uses just two-thirds the energy.
I had to surrender my passport to see it, for I’m at BMW’s highly secure, steel-and-glass research mecca, the FIZ (for Forschungs- und Innovationszentrum, or Research and Innovation Center), an immense complex in Munich replete with workshops, clay modelers’ “caves,” and a vast wind tunnel.
I’m basking in the glow of three of BMW’s brightest lights: project founder Volker Levering, whose laser inspiration—a mental lightbulb, if you will—flashed on during a 2010 Christmas ski trip in the Alps; Stefan Weber, the current program leader; and Helmut Erdl, also among the technology’s inventors.
“A person may not be directly aware, but you can instantly feel the difference between good and bad light,” says Weber, as he switches on a wall of fluorescent panels. I certainly feel the difference: The panels simulate a sunny day above ground, right up to the 6500-kelvin color temperature that photographers consider natural daylight.
These engineers want more than mere intensity: They want a focused, high-contrast white light that mimics that of the sun. BMW’s system will deliver about 5500 to 6000 K—the highest color temperature that international regulations will allow. That level is much closer than today’s headlights to the cool, blue end of the scale, which helps drivers pick out objects and eases eye fatigue.
Until the dawn of semiconductor lighting, the whitest brights any headlights could manage were high-intensity discharge (HID, also known as xenon) lamps, which BMW introduced on the 1991 7 Series coupe. HID light—still an optional upgrade on many 2014 cars—is between 2800 and 3500 lumens and above 4000 K, but it’s weaker, yellower, and less energy efficient than either LED or laser light.
The incandescent bulb invented by Thomas Edison in 1879 has shown remarkable staying power, not least in automobiles. The first LED headlights shone from a car a mere six years ago, when Lexus introduced them on its LS 600h L sedan. Soon, the technological torch may pass to lasers. Laser light will debut in Europe in the 2014 BMW i8, a plug-in hybrid sports car that promises 2.45 liters per 100 kilometers (about 94 miles per gallon) and a 4.4-second surge from 0 to 100 kilometers per hour (or 0 to 60 miles per hour in 4.3 seconds).
The reign of the LED headlight may be ending even before it gets properly under way, says Shuji Nakamura. He should know: Nakamura invented both the blue laser and the blue LED, which made possible the whole world of powerful white solid-state lights. And his Silicon Valley start-up, Soraa, is developing laser systems to complement its LED lighting technologies.
“The laser, we believe, is the next generation of lighting, even for general applications” such as homes, businesses, and a variety of displays, Nakamura says.
BMW’s engineers lead the way to the Nachtfahr, or night-driving simulator. A cutaway interior of a 5-Series sedan, with instrument panel, seats, and steering wheel, faces a darkened simulator screen.
On a nearby workbench rests the culmination of their 2.5-year project: a pair of laser light prototypes, looking like the lethal toys of a James Bond villain. Erdl demonstrates their power, dangling an incense stick into the barely visible beam. The stick immediately begins burning, filling the lab with a cathedral’s scent.
But have no fear: The lasers will be safely contained, with no chance of bouncing their fierce rays off unfortunate retinas, even in the event of a collision. That’s because the BMW lamps turn the intense blue beam into a tightly concentrated but nonlaser—and therefore eye-friendly—cone of white light.
The production version will have up to four Class 4 blue-laser diodes. Collimating lenses will direct their beams onto a phosphorus plate that will convert the laser beams to white light, which will bounce off secondary optics and reflect onto the road. To show me how it works, here in the night simulator lab, Erdl dips a phosphorus wafer into a blue laser beam. The wafer blocks some laser photons and lets others stream through. Among the blocked photons, some stimulate—or “pump”—the phosphorus atoms to emit yellow light. The mix of blue light streaming through and yellow emitted from within produces brilliant white light. It’s the basic technique used, at lower intensities, in most white-light-emitting LEDs.
Indeed, LEDs can approach that 6000-K, white-light nirvana. And for flooding an area with diffuse white light, LEDs are great, Nakamura says.
But he and other experts agree that lasers are much better and more efficient at precisely directing light onto a distant spot. That’s exactly what’s required in automotive lighting (and also in movie theater projectors, which will soon incorporate laser-based lighting systems).
“Wherever you want directional, flexible applications of light, the industry is moving like a freight train in the laser’s direction,” says Paul Rudy, general manager of the laser division of Soraa. “It’s simply the best way to direct light through a complex optical system.”
The reasons are clear. At just 10 square micrometers, the laser’s active light-emitting area is 1/10 000th the size of a 1-square-millimeter LED. That makes it much easier for the laser to focus and project light exactly where it’s needed. The tiny chip itself, with its vastly higher current density, makes it easy to produce dazzling light without multiple, relatively bulky LEDs. And the source is already tightly focused and concentrated, so the tiny movements of the chip can be translated into the large motions of the beam. With an LED, on the other hand, “the light tends to just fan out everywhere, and it’s very hard to focus it optically,” Rudy says.
“With a laser, you combine the high-brightness benefits of a lamp with the reliability, long life, and efficiency of an LED,” he adds. That estimated life, by the way, is 30 000 hours. The lamps could easily outlive the automobile.
Lasers also beat LEDs where it matters most: efficiency. It’s true that LEDs are more efficient at turning electricity into light, though laser efficiency is rapidly catching up. But for overall system efficiency, it’s no contest: LEDs are nowhere near as good at getting the light to where you want it to go. That intense laser, for example, can be beamed into a fiber-optic strand and lose only 10 to 20 percent of its initial energy, as opposed to what an LED could lose—up to 90 percent, experts say. A pair of the old halogen headlights drew about 120 watts from a car’s battery; a couple of today’s best LED headlights draw roughly 40 W. Laser light’s usage is projected to drop below 30 W.
The rise of the technology can be traced back to Nakamura himself, whose first blue lasers hit the market in 2005. Low-power versions were driving Blu-ray players and PlayStations, with higher-power versions reserved for uses such as industrial welding. Engineers kept cranking up the power output in shorter-wavelength, indium gallium nitride chips, until 1-W blue lasers became available. It was a development ripe for new applications.
Digital display makers took a page from LED development, realizing they could also pump the stronger blue lasers into a phosphor to create brilliant light. The result was laser-based “lamp-free” displays, which are now being used in office, school, and home-theater projectors. Rudy calls semiconductor lighting a classic example of a maturing industry, with chip development on a steep upward curve and costs falling rapidly.
“The confluence of adjacent fields really brought laser to the forefront,” he says. “And auto lighting is one awesome example of the application.” Because BMW’s blue-laser diodes measure just 10 micrometers, about one-tenth the length of rival LEDs, you can put them anywhere in an automobile and transmit their output light via fiber optics. That frees designers to create dramatically new headlight forms—or “eyes”—to heighten cars’ personalities and also to save space and redistribute weight.
The field is blowing open, Rudy and Nakamura say. Beyond cars, projectors, and displays, expect to see uses in cellphone “pico” projector displays and future head-mounted systems, such as those now used in Google Glass. Lasers may even end up lighting our homes, offices, stadiums—you name it.
For general lighting, what makes the lasers attractive is that they can be packed much more densely on a chip than LEDs can. Laser-based lights would not only be more energy efficient on a dollars-per-lumen basis but also more flexible, able to work as spotlights or floodlights at the flick of a switch. If costs continue to fall, Rudy says, laser lights could make the leap to general use in roughly 10 years.
BMW intends to introduce the laser-based system on its 2014 i8 plug-in hybrid sports car. As with any plug-in vehicle, the i8 has a particular need to conserve battery electricity for propulsion, as well as for steering assist, entertainment, and heating and cooling. Finding small savings everywhere—even on the order of mere watts—translates directly into more miles of driving range.
Unlike slow-starting, single-brightness HIDs, the laser lights switch on in milliseconds and instantly go to 100 percent illumination. Easy to package in motorized modules, space-saving lasers “offer huge advantages for today’s projection systems,” Levering says.Deer-Spotting Diodes"].
The cars of the future, BMW engineers envision, will automatically adapt to roadway environments by switching among hundreds of lighting programs, if not more. Laser light, Levering says, will dovetail nicely with those developments.
A few hurdles remain. In coming months, BMW’s team must still downsize the system and ensure durability outside the lab. As with LEDs, system cooling is a challenge. Directing airflow over the lamps is an obvious approach, supplemented by motorized fans or conductive materials. BMW is already trekking to Death Valley, Calif., and other locations to test performance in extremis.
The preproduction i8 tucks four laser lights below its stretched hood, but the showroom version will use the laser system for the high beams only. The i8’s low-beam LEDs will emit 50 candelas per square millimeter at their source, compared with 580 cd/mm2 for the laser high beams. That pushes visibility as far as regulations allow. The United States sets a lower limit on total overall light output than Europe does, but automakers generally design systems that can easily be tweaked to pass muster internationally.
As a further safety measure, the i8’s high beams will operate only above roughly 40 km/h, to preclude the possibility of someone’s staring into a static light. Photodiodes will monitor the high-power pumped lasers, switching them off if they fail during a collision or even just as the result of wear and tear. And the system automatically switches to low beams when oncoming cars are detected, as with current adaptive units.
My laser-guided tour of the FIZ complete, I head to BMW World, a dramatically billowing structure nestled among the BMW headquarters, one of its factories, and a tentlike swimming stadium built for the 1972 Olympics. There, throngs of car lovers ogle the i8 and its concept versions, snapping photos like mad, oohing and ahhing over all the carbon-fiber goodness.
It’s all great stuff. But if and when you see your first BMW i8, do Herren Erdl, Levering, and Weber a favor: Spare a little love for those headlights.
This article originally appeared in print as “Whiter Brights With Lasers.”
About the Author
Lawrence Ulrich covers the automotive world from his base in Brooklyn, N.Y.