3 Commonly Used Lighting Technologies in Backlit Membrane Switch Panel Design

One of the main benefits of a backlit membrane switch panel is being able to navigate the equipment or device in low lighting environments. We find backlight keypads and touch panels are more common that you think. Used everywhere from thermostat control in a home to cockpit controls in an aerospace application. Another huge benefit of membrane switches is that they are thin. Ultra-thin when compared to mechanical switches. Thusly, adding thickness to accommodate lighting to a membrane switch is usually undesired.

Many times, designers and engineers find there is just no way to use light pipes or other methods to direct light from a PCB to the desired area of a control panel. Membrane switch manufactures like IP Tech are able to incorporate ultra-thin backlighting solutions into nearly any membrane switch application. By using common technologies like surface mounting LEDs or having electroluminescent layers, membrane switches can provide their own backlighting. When specifying backlighting for applications you should work with a manufacture and use a membrane switch design guide to determine all the possibilities for backlight membrane switch panels.

Lets take a look at 3 technologies commonly used in backlighting membrane switches and graphic overlays used to control equipment or devices.

1. SURFACE MOUNTED LEDs

Commonly surface mounted LEDs are incorporated into membrane switches. Depending on your application, the standard membrane switch may not thick enough to accommodate the package size of a surface mounted LED without embossing it to raise height over the LED.

Surface Mounted LEDs (SMT) mounted to a polyester membrane switch flex circuit.

Very often the overlay needs to be embossed or hydroformed to accommodate the surface mounted LEDs height. It's very important for our engineers to receive drawings showing how the LED’s interface with the electronics. This should be in the form of a schematic. Items to note are the electrical specifications of LED’s and resistors.

2. FIBEROPTIC BACKLIGHTIG

A typical fiber optic lamp consists of layers of woven fiber-optic cloth used to form a rectangular light-emitting area underneath the overlay layer. The fibers coming off one end are then bundled into a circular ferrule and coupled to 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.

3. ELECTROLUMINECENT BACKLIGHTING

Using EL backlighting, or electroluminescent lighting, to backlight devices consumes 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.

Learn more about EL Backlighting