LEDs Continue to Shed More Light

October 09, 2006

Lighting technology has undergone nothing less than a revolutionary change over the past several years as LEDs pushed brightness levels and power efficiency to new heights. Design engineers are continuing to push solid-state lighting technology forward, coming up with techniques to get more light from a single part.

That’s enabling system engineers to be more creative, adding LEDs in new applications or simply replacing existing parts with devices that are far more efficient. The light output of new devices is far greater than their predecessors provided. And as output increases, usage in backlighting and other applications continues to soar.

LEDs work with higher drive currents

The drive current capability of Luxeon K2 LEDs from Philips Lumileds is being increased to 1000 mA, allowing more light output per emitter than any other single-chip LED. The line delivers more than twice the light output 350 mA LEDs, the company claims.

Conventional LEDs usually can’t be driven at more than 350 mA without significantly reducing the emitter life. That limits system designers’ ability to produce more light and reduce cost per lumen. To increase output, Lumileds engineers focused on improving the LED die and the packaging technologies that help manage the additional heat.

Lighting designers can now get more light from fewer devices, minimize their heat-sink requirements, and optimize their system for the exact amount of light required for the application. The line comes in eight colors, including white. David Eastley, Luxeon K2 product manager, predicts that the industry will move to the new drive level just as they did when 350 mA LEDs replaced 20mA parts.

LEDs meet RoHS requirements

Vishay Intertechnology Inc. unveils high-intensity LEDs capable of undergoing lead-free reflow soldering, replacing the company’s TLM series.

The VLM series is targeted at applications including backlighting in automotive dashboards, car radios, and switches; indicators and backlighting in telecommunications systems, audio and video equipment, and office equipment; and for flat backlighting for LCDs, switches, and symbols. The line comes in a broad range of colors including white.

Compatible with JEDEC STD 020b lead-free reflow soldering processes, they feature the same specifications as TLM devices so design engineers can replace existing TLM devices to quickly to meet lead-free soldering requirements. The bright VLM LEDs come in MiniLED packages with up to 50 mcd, PLCC-2 with up to 240 mcd, and PLCC-4 with up to 1250 mcd.

The devices are compatible with IR reflow, vapor phase, and wave solder processes according to CECC 00802 and JEDEC–STD-020b. Pricing in 100-piece quantities ranges from $3 to $14.

IR devices ease system design

OPTEK Technology has expanded its infrared SMD product line with an 880 nm wavelength infrared light emitting diode that delivers a 100 degreeinclusive beam angle. The OPR2800 Series GaAIAs LEDs are housed in a surface mount chip carrier package that matches a PLCC-2 footprint. They come in both single LED packages as well as arrays of SMD package IR LEDs.

“The SMCC package features a flat lens window, which allows a wide beam angle for the LED,” says Alan Bennett, vice president of sales and marketing for the TT electronics company.

The line is designed for non-contact position sensing, data detection systems, machine automation, and optical encoding. Power dissipation is 130 mW at 25C. Operating temperature range for the IR LED is -40 to 100C.

The RoHS-compliant line is available in both bulk and tape and reel packaging. Typical pricing for OPTEK’s OPR2800 infrared LED is $0.90 each in quantities of 100K. Lead time, if stock is not available, is from four to six weeks.

LEDs target mid-range with high output

Thin film technology makes Advanced Power TopLEDs from OSRAM Opto Semiconductors 50 percent brighter than their predecessors. This Power LED range is positioned between standard and high-power LEDs, fitting in applications such as illuminated advertising and effect lighting where standard LEDs are not bright enough but high-power LEDs appear too bright.

At 140 mA, the line has an output of 19 lm in green and amber, 15 lm in white and red, 14 lm in yellow and 5 lm in blue, all 50 percent higher than previous versions. Viewing angles are typified by the 50 percent IV: 120 of white LEDs. Along with white, blue, red, yellow and green are available.

Thin film materials such as InGaAlP and Osram’s ThinGaN white provide high output with low power consumption. Surface mount packages are compatible with standard solder processes. The line is lead free, meeting RoHS requirements.

Fiber optic backlights driven by LEDs

Fiber optic backlighting technology from Lumitex fits in unusual geometries that previously required electroluminescent backlighting. Circles, semi-circles, holes and other irregularities are now possible using UniGlo patented fiber optics configured with new production technology.

When OEMs design membrane switches that aren’t rectangular, UniGlo fiber optic backlights can be positioned between the overlay and the circuit board/metal dome assembly. They are only 0.013 inches thick, so they impact tactile feel the switch dome is depressed.

With brightness as high as 75 ft-L, the panels can backlight an area up to 4 × 6 inches with one LED.

Power consumption is from 5 to 30 mA for a single-LED backlight. The panels, which generate no heat, EMI or ESD, exceed 5 million actuations, with lifetimes up to 100,000 hours. Pricing ranges from $0.70 for a 0.40 × 4-inch panel without LED to $4 for a 1.35 × 3.5-inch panel with a white LED.

Brightness rises as parts count falls

Single-LED molded light guides from Global Lighting Technologies provide higher brightness than other LED-based backlighting solutions, reducing part counts and costs.

GLT’s MicroLens monochrome, bi-color or tri-color backlights can measure from 0.24 to 15.4 inches diagonal, addressing microdisplays in digital still cameras, camcorders, mobile phones, PDA keypads, automotive interior displays, and programmable touch screen thermostats. Chip-on-glass, chip-on-flex LCDs, or the entire display assembly can be mounted into the host, reducing parts count and assembly costs.

The pixel-based light extraction technology makes it possible to integrate backlighting modules with high brightness that are to 0.60 mm thick or less. Their power consumption is typically 1-20 mA at 3.5V. MicroLens’ molded light guide backlights provide what it calls a transition area, which spreads light uniformly, extracting light desired points across the panel.

Simple single-LED backlights cost $1 or less.

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