electroluminescence

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By Steve Baker | Jun 16, 2017
GMN's membrane switch assembly for Welch Allyn.

GM Nameplate’s (GMN) Singapore Division supported Welch Allyn, a medical company, to develop and manufacture a membrane switch panel with backlit indicators for their resting electrocardiogram (ECG) device. As a device used to test a patient’s heart activity, it is critical that the backlighting appropriately indicates how much battery power the device possesses.

GMN offers an array of backlighting options including discrete LEDs, fiber optic weave, light guide film, and electroluminescence. The part had strict spacing requirements between its tactile buttons, which influenced GMN to choose discrete LEDs. Discrete LEDs are cost-effective and ideal for lighting up small indicators.

Instead of using three different colored LEDs, GMN installed one bi-color LED to occupy as little space as possible and reduce costs. The two colors within the LED were green to indicate the battery was charged, and red to indicate the battery was dead. To create the amber color that indicates when the device needs charging, the LED was positioned off-centered from the indicator window to effectively blend the red and green colors together.

Another factor GMN had to consider was the material for the overlay. GMN utilized polyester (PET) film, a common overlay material for devices in the medical industry due to its resistance to abrasion and harsh chemicals. As an extremely durable, long-lasting material, PET film is ideal for applications with tactile switches because it’s abnormal for the material to crack. 

Co Nguyen, GMN
By Co Nguyen | May 18, 2015
Electroluminescence backlighting

Electroluminescence (EL) is a backlighting technology that was first popularized in the 1980s.  It works by sending an electric current through phosphorous that then emits light when charged.     

While a mature technology, Electroluminescence is one of the best backlighting options for giving very even lighting across a large area. Like light guide films and fiber optics, the colors can be controlled via the printed overlay that covers the lit area so there are many options. A drawback to this is that EL is dependent on the color of the printed overlay, while light guide films and fiber optics have the option of changing colors by switching the LEDs used.

There are drawbacks that are also unique to electroluminescence.  There is a half-life of the 4,000 before the phosphorus begins to degrade and the backlighting starts to dim.  In addition, it requires a DC to AC power conversion which can be difficult with many designs. This typically means that it needs to be designed for from the very beginning and is not a last minute drop in feature.  Lastly, it is an expensive option.  Considering the limited life span of the backlighting solution and the price point of this mature technology, it is only a viable backlighting solution in very special cases.  Most new designs are incorporating more advanced backlighting technologies.

To learn more, visit our webpage on backlighting or read our other blogs in this series: