Blue LEDs light disks, bulbs, displays

Whether for night- and general lighting, or in traffic lights (both road and railway) and even full-color TV displays as in Japan, applying blue light-emitting diodes is now a realistic endeavor. Other applications consider the esthetics and economy: they are a cost-effective solution in automotives and sign boards. Entwined with this basic optical application is an area of red-hot activity: white-light LEDs, formed by combining blue LEDs in the same package with various phosphors and/or plastics to undercut the overall cost (especially maintenance) of traditional halogen, incandescent and fluorescent bulbs and lamps.

Present lamp technology across the board—as yet delivered by only a handful of U.S.-established companies that fabricate packaged devices priced at about 50 cents to $1 each in OEM quantities—is represented by a die most often containing gallium nitride (GaN) as the active element on a silicon carbide (SiC) substrate. These devices, generally touted as superblue, superbright or high-intensity, generally have a peak emission wavelength of about 430 nm and a so-called "dominant" wavelength of about 470 nm, which is derived from the CIE chromaticity diagram and represents the single wavelength defining the color of the device. There are two general types, one for concentrated beam widths (tight viewing angles of 10 degrees to 40 degrees or so from the LED's light axis, as measured at the half-intensity points) for dedicated applications, the other for wide viewing angles (~40 degrees to 140 degrees ) and general illumination. Luminous intensity varies from a few millicandelas to upwards of 400 mcd typical output, customarily specified for a forward current of 20 mA.

The user generally has a choice of lens colors and characteristics, radiation pattern and package size. Ga/SiC represents a later alternative to GaN on sapphire (aluminum-oxide) devices,which have a peak emission wavelength of about 465 nm and are somewhat brighter but also considerably more expensive. Also on the scene are some InGaN units, which may ultimately provide both cost and performance advantages. Today's devices in general provide up to a tenfold improvement in output power over silicon carbide, the original active element in blue LEDs.

Sharp (Camas, Wash.), one of the first recognized commercial names in blue LEDs, has its GL5BX64, a GaN/SiC lamp which provides 100 mcd (typical) with narrow viewing angle.

Sharp also appears to be the first with red/yellow/green/blue full-color dot matrix LED units for indoor use, as seen in its IC-like LT1550, -1560, and -1580W series (16 x 32 dots), which have a built-in driver, shift register and latch circuit.

Perhaps the widest range of devices so far come from QT Optoelectronics (SUNNYVALE, Calif.), which has the MV8Bxx Series providing luminous intensities ranging to a maximum of more than 1,500 mcd. These include T1-3/4 superbright blue LEDs having narrow viewing angles of 10 degrees (MV8B11) and 24 degrees (MV8B01) for concentrated light output. Their GaN/SiC technology delivers a minimum luminous intensity of 400 mcd (typical is 1,000 mcd).

One LED for applications in backlighting display panels and coupling into lightguides comes from Siemens (Cupertino, Calif.). Its Argus LED, in a T1 package, includes the LB K376, which has a custom-built reflector. It provides a minimum luminous flux of 10-25 mlm (max 16-40 mlm). Other devices for use as an optical indicator include the LB3336, 5416, 5436 and 5456 lamp type LEDs in T1 and T1-3/4 packages with a luminous intensity up to 125 mcd at forward current of 10 mA.

Hewlett-Packard's (SANTA CLARA, Calif.) entry into the blueLED market, while only recent, may yet provide a few surprises in brightness owing to InGaN technology. The T1-3/4 lamps in their initial HLMP-CBxx line of untinted, non-diffused devices with a dominant wavelength of 475 nm, feature a minimum output of 250-630 mcd (typical 450 to 1,100 mcd) for viewing angles of 15 degrees to 30 degrees . In addition, its HLMP-AB01, specifically for full-color video outdoor signs requiring an oval radiation pattern (35 degrees to 70 degrees ), delivers 400 mcd (typical). The HLMP-AB01 is priced at 72 cents/million pieces.

Micro Electronics Corp. (SANTA CLARA) offers a GaN (and InGaN) devices on SiC, the latest of which is its 430-nm MBB lamp series of "high intensity" LEDs. The MBB51, in a diffused lens, is encapsulated in a T1-3/4 standard package with a 40 degrees viewing angle and typical output of 25 mcd. It comes in a clear transparent lens, with a 20 degrees viewing angle and a minimum output of 200 mcd (300 mcd typical). The MBB32W, also in a clear diffused lens, has a 50 degrees viewing angle, and typical luminous intensity of 18 mcd. These devices operate over -20 degrees to +80 degrees C.

Stanley Electric (Irvine, Calif.) has just released three lamp-type designs and two chip-type SiC designs. The lamp series delivers luminous intensities up to 250 mcd, and viewing angles of 10, 20 and 70 degrees. The chip-type LEDs are available with a luminous intensity up to 30 mcd and a viewing angle of 40 degrees or 140 degrees .

QT Optoelectronics surface mount blue-LED lamp, the QTLP652C-B, fits the industry-standard chip type 1206 for panel illumination, push button backlighting and membrane switch applications. With a wide viewing angle (140 degrees ), the lamp delivers a minimum of 20 mcd (30 mcd typical). Its QTLP670C-B, in a two-pin PLCC package with a flat top and sides for automatic placement equipment, is compatible with convective IR and vapor phase reflow soldering and conductive epoxy attachment. Their -RB device is a bi-color device, in a four-pin PLCC, employing an AlGaAs red and InGaN/SiC blue. Others include QT's HLMP-6B00A subminiature (T-3/4) square-base LED lamps, which are available as a surface-mount or axial leaded device.

Siemens' chip-type devices address backlighting applications. They include the 430-nm Blue Line of Hyper SideLed, TopLed, and Argus LED families. The SideLed LB A676 and the LB C876 in the Mini SideLed family, surface-mount end-view devices suitable for backlighting and coupling into light pipes and lenses, deliver a minimum 4 to 10 mcd (maximum 6 to 16 mcd) at 10 mA over a 120 degrees viewing angle (luminous flux is typically 15-40 mlm).

At the other end of the viewing scale is the 5-mm LED lamp, the LTL-353UBK, with a peak emission wavelength of 428 nm and a typical luminous intensity of 250 mcd at a viewing angle of 12 degrees . The LTL-353UBK sells for 92 cents each per 10,000 quantities; the other LEDs are priced at 66 cents each per 10,000.

Most recently, Sharp has just released two leadless chip devices, the side-emitting LT1BC45A and the top-emitting, 1608-sized GM1BC55200A, which deliver 4.5 and 7 mcd (typical, forward current of 30 mA) at a viewing angle of 100 degrees and 80 degrees , respectively. Other surface-mount entries include Kingbright's, (City of Industry, Calif.) which now offers compact blue (430-nm) devices ranging from 1.6 by 0.8 mm to 3.2 by 1.6 mm and a profile as low as 0.65 mm.

Generating white light from a blue LED for general-purpose lighting applications is quickly catching favor. Here, the blue LED is placed in the same package as a yellow phosphor (e.g., yttrium aluminum garnet), with the process-controlled interaction of light with phosphor creating a variety of hues.

In a separate development related to white-generating devices, a single-pixel white display has most recently been demonstrated with light-emitting red, green and blue polymers, on the way toward full-color LED applications (See Feb. 15, page 26).

As for the most-recent practical white-light LEDs, Siemens has just announced a 20-mcd device in its TopLed design, the LW T676, which sells for $1 each in 10,000 quantities.

A catalog entirely devoted to white LEDs is now available from Data Display Products (El Segundo, Calif.), which packages basic devices supplied by Nichia. And from the business side, GE Lighting and Emcore have recently united to target the white LED market, with products that are due out in the second half of this year.

COMPANY CONTACTS

Hewlett-Packard Co.
(800) 537-7715
www.hp.com
EETInfo No. 601

Kingbright
(909) 468-0500
www.kingbright-led.com
EETInfo No. 602

Lite-On Inc.
(408) 946-4873
www.liteon.com
EETInfo No. 603

Micro Electronics Corp.
(408) 988-1101
www.microelect.com
EETInfo No. 604

QT Optoelectronics
(408) 720-1440
www.qtopto.com
EETInfo No. 605

Sharp Microelectronics
(360) 834-8941
www.sharpsma.com
EETInfo No. 606

Siemens Microelectronics Inc.
(408) 777-4500
www.siemens.com
EETInfo No. 607

Stanley Electric
(800) LED-LCD1
www.stanleyelec.com
EETInfo No. 608