Designing the right backlighting technology into a membrane switch assembly can help deliver a superior user experience. A wide variety of backlighting options are available, allowing engineers to precisely manage light quality, color, intensity, and coverage, so it is important that your selected switch manufacturer understands the advantages and disadvantages of these different techniques.
Solid-state electroluminescent (EL) lamps produce light by charging phosphors with AC/DC current. They are highly efficient and provide an extremely even appearance. In membrane switch assemblies, EL lamps are typically implemented as a panel just beneath the graphic overlay. They do require an alternating current source, so they are not appropriate for all applications. However, in devices that already feature inverters, EL lamps can be an ideal backlighting option.
By shining an LED through optical fibers, engineers can illuminate very specific parts of a membrane switch. This precision, combined with the low cost and low temperatures associated with fiber optics, make this a preferred technique for many applications. However, depending on the number of fibers that are brought together at an LED, there can be a bulky pigtail. To overcome this physical limitation, many designers will specify woven, fiber optic pads. These can be expensive, but they result in a compact, low-power highly controlled backlighting result.
With LGL – Light Guide Layer technology – a light-diffusing plastic material is used to evenly backlight broad areas with LED sources. LGL is more cost-effective than woven fiber optic pads. However, more LEDs are required to achieve the same backlighting effect, so while LGL can be a very good choice for high-volume, low-cost applications, this approach does require more components. Manufacturing automation can become a critical deciding factor when implementing LGL technology.