Searching for a better bulb

Watch out, Edison: A new contest aims to replace the inefficient common light bulb with brighter and better concepts in solid-state lighting. That's because traditional incandescent bulbs waste a lot of energy, converting less than 10% of their total energy into useful light. To speed the search for a better bulb, a competition sponsored by the U.S. Dept. of Energy (DOE) will award significant cash prizes, as well as opportunities for federal purchase orders and other incentives. Named the “Bright Tomorrow Lighting Prizes” — “L Prize” for short — the contest will pay $10 million for the first 60-W A-19 incandescent bulb replacement to match the contest specs, and another $5 million for the first PAR 38 halogen replacement. A third prize, called “21st Century Lamp,” will be awarded for a new concept in lighting, going beyond the two retrofit prizes.

The L Prize came out of the Energy Independence and Security Act of 2007 and was officially announced by DOE in May 2008. It is the first contest of its kind to be sponsored by Uncle Sam and its goal is nothing short of revolutionizing the way America lights up. The DOE estimates that if every 60-W bulb socket across the country converted from today's incandescent bulb to the L Prize winner, consumers would reap more than $2 billion in energy savings.

Contest rules make it clear that the winner won't be a one-of-a-kind lab experiment. The complete entry must include 2,000 samples and a manufacturing plan that details capabilities for mass production. Contest entrants must be U.S. companies using U.S.-made LED chips in their designs. All entries will undergo stringent tests during a yearlong process to determine performance, manufacturing capabilities, and finally, 6,000 hours of lifetime testing. Tests will put entries through extreme environments, humidity, high heat, voltage fluctuations, electromagnetic interference, and more to determine failure modes and product weaknesses.

Game on: Ready, set, glow

The degree of difficulty involved in the creation of a winning replacement bulb is anybody's guess. Opinions vary widely. For example, Jordon Papanier, marketing manager for LEDtronics Inc., Torrance, Calif., believes thermal management issues could be sticking points.

“Thermal management requirements for the high-power LEDs, including 1, 2, 3, and 5-W models, are the biggest problem in designing and making an LED bulb that puts out an even 900 lumens of light in 360° in a standard A-19 bulb package size. There's just not enough room in the A-19 bulb to achieve this with the LEDs currently available,” says Papanier. “The other limitation is price. Not many homeowners will be willing to pay $90 and up for a general room light LED bulb. The payback in energy saving is just not that attractive for the average home. There are some LED bulbs on the market claimed to be equal in light to an A-19 incandescent bulb, but they're only putting out 440 lumens in a narrow beam angle, like 112° from the top of the bulb. This is misleading and gives LED bulbs a bad name in the general room lighting marketplace.”

“The current bases [of existing 60-W bulbs] are not well suited for thermal management, which makes it difficult to design LEDs that will be a retrofit into the installed base of sockets out there,” says Dr. Kevin Dowling, vice president of innovation at Philips Color Kinetics, Burlington, Mass. In the long run, he believes new bases and new lighting schemes will likely be developed, allowing designs that can incorporate better thermal management and better optics as well. Some of the new systems could also involve Ethernet-based control systems, where lighting could be controlled remotely over a Web browser.

Dowling is among those who think LEDs for general illumination are relatively close to becoming an everyday lighting option. He believes lighting technology is evolving at the rate of Moore's Law, similar to the exponential advances seen in computer technology and says we're less than two years away from general illumination products on store shelves. “We're already seeing commercial scale installations of LEDs at churches, restaurants, and large construction projects, as well as in high-end residential settings,” notes Dowling.

However, he feels the most difficult L Prize specs involve color issues, due to manufacturing variation. “The problem is that even small wavelength shifts can be detected by the eye and will register as slightly different colors or brightness levels. The color issues must be worked out before bulbs can be sold to consumers on a mass scale,” he explains.

Right now, there don't seem to be any L Prize frontrunners. “Anyone can submit a good idea,” Dowling emphasizes. “The DOE is looking for all the quality ideas out there, and the prize criteria is not meant to exclude anyone. A small company may need to partner with a larger one to produce the 2,000 required samples, or to go into mass production, but the contest is open to everyone.”

The consensus among experts seems to be that winning the L Prize will not be easy. “The L Prize performance requirements are definitely challenging, and it's the combination of requirements, all to be met in one product, that's the trick,” says Kelly Gordon, program manager at Pacific Northwest National Laboratory. “But to be a truly viable replacement for a 60-Watt A-19 incandescent bulb, the LED product must provide equivalent light output (900 lumens), warm color appearance (2,700 K to 3,000 K), and excellent color rendering (at least 90 CRI). The form factor of an A-19 lamp does present a challenge for thermal management, in that there is limited area to use as heat sinking material to dissipate heat from the LEDs and associated electronics. The PAR38 replacement has more heat sink area to work with, but also higher flux (1,350 lumens) and efficacy (123 lm/W) requirements to be met,” says Gordon.

Nevertheless, the L Prize is getting a lot of support. Some 30 utilities and regional entities have joined DOE as L Prize Partners.

Sally Lee, applications marketing manager at Osram Sylvania, Danvers, Mass., also calls the L Prize requirements difficult, but says the challenge is good for the lighting industry. “The L-Prize will be a great gate review of how accurately DOE predictions for SSL advancements align with the U.S market's interest in a new tradition in warm white architectural lighting technology,” she says.

“Benchmarking approximately seven times lm/W and much longer than 25 times average rated life is exciting for manufacturers because it sets a level playing field. In addition, there are further challenges in the requirement for even intensity from 0° to 150° from what is essentially a Lambertian source. The same can be said for the >90 CRI requirement when CIE (The International Commission on Illumination) has flatly stated — in a DOE SSL publication — that CRI is not an accurate metric, in its current state, to describe SSL. I'm excited that the entries must all be dimmable to 20%, a target that CFLs (compact fluorescent bulbs) missed, which is a sign that lessons were learned from CFL technology,” says Lee.

A LITTLE LED HISTORY

The first LED, developed at General Electric in 1962, was a red LED producing 0.001 lumens. During the 1960s through 1980s, first red and then green LEDs were developed, and light output grew from 0.01 to 0.1 lumens. In the 1990s, Nichia created the first blue LED, which emitted 1 lumen and led the way to the development of white light from LEDs — achieved either by mixing light from red, green, and blue LEDs (known as RGB systems) or by coating a blue LED with phosphor to emit white light, known as phosphor-converted or PC LEDs. In 2008, white LED devices capable of emitting close to 100 lumens from a nominal 1-W device became commercially available, with further improvements taking place throughout 2009.

Major research challenges must still be addressed before the full promise of solid-state lighting is realized. Color quality continues to improve; many white LEDs available today have high color temperature, meaning they look cool/blue, and there is significant drop-off in efficacy with warm white LEDs. Thermal management is also critical to LED system operations. While LEDs don't emit infrared radiation from the front (i.e., the “bulb” is cool to the touch), they produce heat that must be removed from the diode to avoid a drop in light output and shortened life. Over time, LEDs get dimmer and their light output diminishes faster in high temperature environments. They are considered “done” when light output falls below 70% of initial brightness.
Source: Kelly Gordon, Pacific Northwest National Laboratory

CALIPER COMPARES PRODUCTS

Commercially available products are independently tested through a program called CALiPER (Commercially Available LED Product Evaluation and Reporting) run by DOE and available on their website. The testing helps consumers and manufacturers alike compare LED products.

As far as lifetime testing, the hype touting LEDs as having a useful life of 100,000 hr is incorrect. So say engineers at Philips Lumileds Lighting Co., San Jose, Calif. “The technology for 100,000-hr, high-brightness LEDs doesn't exist,” says application engineer Pat Goodman. “We have published what is probably the longest database on lifetime data and it only goes out to 9,000 hours. To extrapolate from 9,000 to 100,000 hours is quite a stretch.” To learn more, visit www.machinedesign.com and type “100,000-hour LEDs” into the search box.

LEDS MOVING TO PRIME TIME

Ever more white light LED products are coming to market. Readily available LEDs include portable desk and task lights, under-cabinet lights, recessed downlights, retail display lights, and outdoor lighting for street, parking lot, and path illumination.

CONTEST SPECIFICATIONS

Meeting the L Prize requirements will not be an easy task, though the rewards are great. Here are some of the specifications the DOE is looking for:

Thermal management Manufacturers must adhere to LED device manufacturer guidelines, certification programs, and test procedures for thermal management.

Dimming Products must be compatible with at least three residential dimmers, and must be dimmable to at least 20% of maximum light output.
Visit www.lightingprize.org for complete L Prize requirements.