Figure 1a Fiber optic technology has developed to make the most out of the brightest LEDs, spreading their light efficiently and flexibly, while minimizing power, circuitry and LED count. Fiber optic backlighting, in particular, is an increasingly popular way to differentiate product designs with light, increasing clearly-perceived customer value. Fiber optic panels couple with LEDs to provide more flexible, adaptable and cost-effective alternatives to such common technologies as molded plastic light pipes, EL, LED arrays, discrete (embedded) LEDs and CCFLs.
Figure 1c Lumitex offers a range of patented fiber optic technologies that provide RoHS compliant, custom backlighting solutions for membrane switches, keypads, overlays, LCDs, and other displays, as well as custom fiber optic devices, surgical and phototherapy lighting systems (see figures 1a, 1b, 1c). elastomer rubber switches
For fiber optic technology, LEDs are the most ideal light source because they provide a focused point light source that can be easily coupled into the optical fiber. Fiber optic panels coupled with LEDs are also inexpensive, durable and have a long lifetime of more than 100,000 hours in most configurations. Commonly used colors are white, green, blue, aqua, amber, red, RGB and infrared. Lamp style (5mm or 3mm) round LEDs mate well with optical fiber panel technology.
Design factors to consider Fiber optic technology is ideal for sensitive applications that require light without heat, electricity or EMI. In the case of unusual geometries, fiber optic lighting can backlight rectangles, ovals, circles, semi-circles and go around holes. For uniform area lighting, fiber optic backlighting can spread light from a single LED over a larger area than any other technology. This is particularly important for LCDs in low-power, hand-held devices and is superior to embedded LEDs when used in membrane switches and overlays.
In terms of complexity, EL and CCFL backlighting require an inverter, and LED arrays can consume more power, which may require circuit re-design. Fiber optic, LED-driven backlighting uses direct current, with no inverter or design changes necessary. When it comes to durability, the technology is virtually indestructible in most applications, and is completely RoHS compliant.
Thin and flexible panels such as Lumitex’s UniGlo® product are ideal for membrane switches. The UniGlo panel is placed beneath the overlay and above the circuit board/metal dome assembly (see Fig. 2). There is sometimes a spacer layer that goes above the circuit board, around the domes and below the fiber optic panel. The flexible nature of the fiber optic panel preserves the tactile feel when the user presses through the overlay to actuate the domes. The fiber optic tail is routed, around any obstacles to the LED, which is designed into an appropriate space on the circuit board.
Done properly, backlighting an LCD does much more than just making it readable. Attention to detail, combined with the right illumination technology, can enable its information display to give the appliance a whole other dimension in term of aesthetics.
Figure 4a In high-end audio equipment manufactured by McInTosh (Binghamton, NY) for example, the backlight must do more than provide a high degree of light output. It’s important that it be perfectly uniform, consistent, and provide just the right color the manufacturer wants. The incandescent backlighting used for the large power output meters in their top-quality power amplifiers was causing a blue tint around the edges that became progressively more washed out toward the center (see Fig. 4A).
Figure 7 Fiber optics can also be used to provide just right color and mood for illuminating control panels for hospital beds. Other medical applications include switches and overlays, controls, and nameplate lighting and flexible light panels that help surgeons see during deep-cavity surgery. Full-Travel Keyboard & Computer Applications
The translucent keys are illuminated by the light from the panel shining through the die-cut hole for each key. When used to backlight flat panel membrane switch keyboard overlays, the UniGlo™ panel is placed between the translucent keyboard overlay and the membrane switch (metal or plastic domes, or non-tactile switches). A single-layer UniGlo™ panel adds only 0.2 to 0.8 ounces of additional snap-through pressure (depending on the type of dome being actuated).
backlit user interfaces New (and Future) Applications The versatility of LED-based fiber optic backlighting and illumination technology is such that applications are almost limitless, and new ones are cropping up all the time, making it popular with design houses that specialize in new product invention and design development. It is proving to be an effective solution for applications as diverse as backlighting the instrument panels in trucks, busses and in the cabs of off-road vehicles used in construction and agriculture to accent lighting for tanning beds to the illumination of the vests used in games of laser tag.