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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 13, 2015
Keypad with light guide film backlighting

If you have read our previous posts in this backlighting series, you should already know what questions to ask before starting a backlighting project as well as when to use discrete LEDs.  Now we’re going to go over the next backlighting technology, light guide film. 

Light guide film, much like it sounds, uses a thin film to guide the light from LEDs to the areas that need to be lit.  The film is has a reflective coating on a bottom and top layer of film.  The top layer is laser etched/abraded in the areas that you want light to escape and light your overlay. The etching pattern can be altered to control and allow certain areas to be brighter or dimmer, helping to eliminate hotspots.

Right angle LEDs are used when using light guide film. The right angle LEDs need to be butted up against the edge of the light guide film (whether the actual edge of the light guide or an edge inside a cutout in the light guide). Placement of the LEDs depends on several factors and will be determined by the engineer and vendor.  

Though it can be a more expensive backlighting option, light guide film may soon become the standard backlighting option because it has many advantages.  It can be designed very thin so it works well in small, light devices, and it has limited impact on the tactile feel of buttons. It is also a great solution for lighting large areas while still maintaining a mid-range price point. 

Some common challenges with light guide film can be light leaks around part edge and hot spots around the LED area. Light leaks can be overcome by using an opaque panel filler around the light guide. Hotspots around the LED can be avoided by making adjustments to the printing process of the overlay.

Light guide film generally struggles with lighting the same icon multiple different colors due to placement of the LEDs. Regardless of the drawbacks, we anticipate that light guide film with continue to grow in popularity and that the challenges will be minimized as the technology evolves.  

Read our other backlighting blogs: 

Co Nguyen, GMN
By Co Nguyen | May 5, 2015
Backlit touchscreen

This month we are kicking off a five-part blog series on backlighting.  The series will begin with an overview of how to approach a backlighting project and then each subsequent blog will review one of the four most popular options in backlighting: discrete LEDs, light guide film, fiber optic weave and electroluminescence.  

GMN frequently works with customers to integrate backlighting solutions into products including membrane switches, displays, and even branding pieces such as nameplates. We’ve developed applications for industries as diverse as appliance, medical, automotive, and more.

To establish the best backlighting solution without hotspots (uneven brightness, usually due to the location of LEDs) or light bleed (light coming through where it shouldn’t), the first step is to create a list of necessary requirements and assess the proposed design.  Start by asking these questions:

  • In what type of light will the device be used? Will the backlighting need to be visible in bright sunlight, the ambient light of offices, dark hospital rooms, etc.?
  • What needs to be backlit?  Is it a full screen, keypad, specific buttons, status or discrete indicators, a combination?
  • What colors will be used and where? 
  • What are the power requirements? 
  • What are the space constraints?
  • If there is a keypad or buttons, what type of tactile feedback is required? 

Based on the responses to these questions, you should be able to evaluate which backlighting solution, or combination of backlighting solutions could work with your device. 

Learn more about backlighting from one of our other blogs: