Backlighting Options - Esterline Interface Technologies - #3

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Design considerations • Color is determined by the light source. • Tactile feel can be reduced in a Flat Panel Dome-style product.• Localized holes for switches or other items are generally not feasible. Light Emitting Diodes (LEDs) Light emitting diodes offer many attractive featuresincluding multiple colors, and variable intensity adjustment.These devices are made by encapsulating LED chips on axial lead frames to form molded epoxy subminiaturelamp packages. Some LEDs have high light output foruse outdoors, making them easily seen in direct sunlight.Newly developed, low thermal resistance, high flux outputLED lamps are now available. These new devices allow operation at higher-than-normal drive currents and producesufficient light output to reduce the number of lampsneeded to backlight existing designs or designs in process.One of the most common reasons LED displays are designedinto an application is their high level of reliability. Other benefits include long life (typically more than 100,000hours), low cost depending on color and intensity, anda variety of package configurations. In addition, LEDs operate on low voltages, create low electrical powerdissipation, and emit little heat. Aesthetically, they offeran array of viewing angles and a wide range of color choices. An important consideration with the use of LEDs is thatlight diffusion can be problematic in certain applications.LEDs are the most widely used method of backlighting.They can be used to illuminate discrete legends, entirekeypads, individual keys, or selective combinations of each. Implementation and product construction varygreatly, depending on switch technology. LEDs are oftenused in mid-travel products. The elastomer switch can be fabricated in clear or translucent colors and is generallyhelpful as a diffuser to even out light intensity. customers with a combination of quality, long life,environmental stability, economy, and extremely even lightoutput over surface area.Typical design implementation involves the lamination ofan EL panel behind a graphic overlay. The graphic overlayis selectively printed with translucent or clear regions orlegends to allow light transmission. A majority of products,with EL lighting are Flat Panel or Flat Panel Dome-styleproducts. When implemented in a Flat Panel Dome, theextra thickness of the EL panel can reduce the tactile feel of the dome switches. Design considerations • LEDs cannot be located directly over or under switch pads. • LED package size can limit placement options.• Keypad construction can impact lighting performance. Design considerations • Options for color are limited.• Mechanical size of DC/AC inverter must be considered.• Fabrication of custom EL panel requires die-cut tooling. Plastic Optical Fiber (Optical Fiber) Panels can be woven from plastic optical fibers and caused to emit light. The thin, flat panel is free of heat andelectromagnetic interference. It provides significantdesign flexibility. Advantages of backlighting with plasticoptical fiber devices include longer life, lower powerrequirements, uniform brightness, and a thin profile. Thefact that fiber optic panels do not emit heat or generate electromagnetic interference is important in someapplications. In addition, optical fiber is not affected byextremes in humidity and temperatures. These panels are easily powered by LEDs or Halogen lamps. Halogen lampsare typically required for sufficient brightness. Important considerations with this backlighting techniqueare as follows: Optical fiber components are costly in low volumes, lead times are typically longer than alternate light sources;and depending on panel thickness deadened tactile feelcan be a result.Designs using optical fibers have generally been limitedto flat panel or Flat Panel Dome style products. The panel is generally laminated behind the graphic overlay, similarto an EL panel. Due to the need for conductive switchesto contact a circuit, it is impractical for an optical fiber panel to be used in mid-travel or full-travel productssince locally routing fibers around switches is notgenerally feasible.