Membrane Switch Backlighting

Enhancing the User Experience

What are the Backlighting Options for Membrane Switches?

One of the ways to enhance the user experience and differentiate your equipment from the competition is to incorporate backlighting into the membrane switch design. Backlighting involves strategically placing lights into the membrane switch construction to make keypads, legends, and displays easier to read. There are specific cosmetic and cost advantages and disadvantages to be considered, based on the backlighting method employed. Pannam can guide you in the most cost-effective backlighting technique for your user-interface assembly, and offers a complete range of backlighting technologies, including:

  • Light Guide Film (LGF)
  • Light Emitting Diodes (LED)
  • Electroluminescent (EL) Lighting
  • Fiber Optic Lighting

Pannam Imaging also offers other backlighting membrane switch options such as a dead-front area, which features icons that are invisible until luminated.  Continue reading below to learn more about these backlighting technologies and options.

Light Guide Film (LGF)

light guide filmLight Guide Film (LGF) is a thin film backlighting technology that will direct light produced by side-firing or right-angle LEDs across the area that needs to be backlit.
The advantage of LGF is that the film can be fabricated into almost any shape, providing consistent backlighting across one or more areas within the switch.

Multiple LGF films can be used within one application to provide discrete backlighting to different graphic features.
Different colored LEDs can be used to achieve unique lighting effects or white LEDs can be used to light different printed graphics on the overlay.

Although Light Guide Film can be more expensive than other backlighting technologies (below), it has several advantages:

  1. The LGF is extremely thin so it can be incorporated into membrane switches that can’t exceed a certain thickness (i.e. small, lighter devices)
  2. LGF has limited impact on the tactile feel of buttons.
  3. LGF can provide even backlighting across large and small areas, including applications where the light remains on while the switch is powered.

To learn more, review the “How to Implement Light Guide Film (LGF) Backlighting” whitepaper.

Light Emitting Diodes (LED) LEDs

light emitting diodesLEDs are used primarily as indicator lights, and are a popular, low-cost, point-source lighting method. Embedded LED’s emit very little heat, and come in a variety of colors including red, yellow, green, blue, white, and bi-color lamp packages. Various intensities are available, some of which are especially designed for viewing in outdoor environments.

Surface mount LEDs can be bonded into our polyester switch constructions, which provide a reliable, cost effective light source. An even greater variety of lamp packages can be used in PCB Membrane Switches and Copper Flex Membrane Switches, and can be through-hole soldered, which enhances durability.

Other features of LED backlighting include:

  • Reliability and long life – typically more than 100,000 hours
  • Low cost
  • Efficient power consumption, operating on low voltages
  • Available in a wide variety of colors, intensities, and lamp packages

Electroluminescent (EL) Lighting EL

Electroluminescent lightningEL lamps contain phosphors, which convert electrical energy directly into light energy. The high efficiency of this conversion minimizes power consumption and losses due to heat or IR emissions. EL backlighting devices consequently consume relatively little power under normal operation. They are best suited for low and no light applications where the backlight is not always on, because the phosphors tend to decay with extended use at high voltages and frequencies. The useful life of an EL lamp will vary depending on the quality of the phosphors and how hard the lamp is being driven.

Some additional features and design considerations for EL lamps are:

  • EL lamps consume very little power
  • Provides uniform, balanced backlighting of the entire membrane switch area
  • Requires a DC to AC inverter to operate
  • Thin profile and durability make it suitable for most membrane switch constructions
  • Limited color options are available

Fiber Optic Lighting

Fiber Optic Lighting A typical fiber optic lamp consists of two or more layers of woven fiber-optic cloth used to form a rectangular light-emitting area. The fibers coming off one end are then bundled into a circular ferrule and coupled to one or more LED light sources. Fiber optic lamps are a cost-effective method to achieve more uniform backlighting across a broader area of the membrane switch keypad. With fiber optic backlighting, light from a light source, normally an LED, is evenly distributed under the graphics by use of very thin plastic fibers. Some additional features and design considerations for fiber optic lamps are:
  • Longer life vs. EL lamps, typically 100,000 hours based on a typical LED
  • Very low power requirements – 20-50 mA with an LED
  • Uniform brightness for backlighting large membrane switch background areas
  • Fiber optic lamps do not emit heat or generate electromagnetic interference
  • Withstands extremes temperatures and humidity