LEDs and plastic fiber take on multiple applications

STRONGSVILLE, OH-The purpose of optical fiber is to guide light along a longitudinal axis, but Lumitex is exploiting advantages to be obtained by defeating that purpose, for instance in creating optically interactive apparel for people who play laser tag.

STRONGSVILLE, OH-The purpose of optical fiber is to guide light along a longitudinal axis, but Lumitex is exploiting advantages to be obtained by defeating that purpose, for instance in creating optically interactive apparel for people who play laser tag. The laser tag vest emits light of appropriate color (either blue or green) to designate the wearer’s team. The emitted color changes to red, when the wearer is “tagged” by a laser beam, but only when the wavelength indicates that it came from a member of the opposite team. The vest is woven of plastic (acrylic) optical fibers that carry the incident laser light to a photodiode and controlling circuitry for a 3-chip RGB LED array.

The weaving method enables light to be transmitted not just along the axis of a fiber, but also through the sides of one fiber into adjacent fibers. Lumitex uses two techniques. One uses optical fiber woven into a cloth to create layers that can be built up into a panel or other lighting device. Another technique, dubbed “Uniglo”, uses optical fiber mounted on a back reflector to create lighting panels as thin as 0.013 inches. In both cases a computer controlled etching process ensures uniform light distribution, and both methods are used in single or multiple layers along with laminates to produce lighting panels in custom shapes, sizes and configurations.

The first major product success at Lumitex was the BiliBlanket, sold through GE Healthcare (Chalfont St. Giles, UK), that allows infants being treated for jaundice to be simultaneously held and cared for. Unlike laser tag vests, the BiliBlanket uses HID illumination, which was the dominant light source at the time and remains so for many applications (particularly medical). POF melts at 104 degrees C, so glass mirrors are used at the launch end with high power incandescent sources to reflect/filter out high-end infrared radiation.

Incandescent sources for fiber illumination have progressed to the point of being used to light body cavities during surgical procedures, such as hip replacement, which can now be done with a 3-inch incision instead of the traditional cut from hip to knee, according to Lumitex president Peter Broer. Breast reconstruction can be performed in a 1.5- to 2-inch space vs. a 3- to 4-inch cut.

Light sources used in the early 1990s were mostly incandescent because LEDs could not compete. But by the mid-90s, LED technology had boomed with increasing colors and higher power output, and today, 90% of applications in the electrical world are LED or diode based. However, in the medical world, incandescent lights still dominate. To get away from the flicker of HID and quartz halogens, however, the industry is beginning to migrate to DC light sources (LEDs) and are even being used in operating rooms for ambient area lighting.

Product offerings at Lumitex, which has been launching LEDs into fiber since the early 1990s, have migrated through these source changes and are now looking toward lasers. The laser tag game is a forerunner in this.

“Lasers are emerging as a source, but we don’t know yet what the customer demands will be,” Broer said.

A currently important application for LED illumination through optical fibers is membrane switches, activated by a tactile sensor beneath an overlaid display. Traditional membrane switches have been rectangular in shape, Broer said, but some OEMs have been designing membrane switches with other, more unusual shapes to help differentiate their products in the marketplace. Applications include HVAC controls for commercial refrigeration, programmable thermostats that can ramp up and down, hot tubs and spas, and medical devices. -Hassaun A. Jones-Bey

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