Backlighting technologies: Electroluminescence (part 5 of 5)

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By Steve Baker | Oct 22, 2020
Electroluminescence backlighting

In this final blog of our five-part series on backlighting, we will be looking at electroluminescent lamps in detail. In the first blog, we discussed how to approach a backlighting project and reviewed the different backlighting solutions in the subsequent blogs, namely discrete LEDs, light guide film, and fiber optic weave.

What is electroluminescent lighting?

Popularized in the 1980s, electroluminescence is a technology that works by sending an electric current through phosphorus, a semiconductor that emits light when charged. Electroluminescent (EL) lamps can be mounted on printed membranes or printed circuit boards.

Advantages of electroluminescent lighting

Governed by the design requirements, EL lamps can be zoned in selective areas to ensure optimum diffusion of light. With minimal light bleed, it doesn’t require blocking layers between different sections that are lit. Like fiber optic technology, EL lamps can also be integrated with discrete LEDs to have indictor lights and light up large areas simultaneously. Some of the advantages of EL backlighting technology include –

  • Ability to illuminate large surfaces
  • Limited impact on the tactile feel of buttons or domes
  • No light bleeds
  • Varied color options via overlay printing

Unlike light guide films and fiber optics where the light color can be changed at the source, there are certain limitations with the EL backlighting method. The core colors that phosphorus can produce are white and blue-green. While generating other exotic colors is possible, it can significantly add to the cost of the design. One way to navigate this shortcoming is to have the EL light in one color (preferably white) and then print the graphic overlay in the desired color scheme. If you need different colored lighting for separate areas, the sections can be isolated by adding additional traces.

Disadvantages of electroluminescent lighting

The biggest limitation with EL is the half-life of phosphorus. After 4,00 hours, the phosphorus begins to degrade, thereby dimming the backlit area. EL also requires a DC to AC power conversion which may not be possible to integrate into many designs. This typically means that EL backlighting needs to be designed in from the very beginning of the design cycle and cannot be added as a last-minute drop-in feature. The main challenges with EL include –

  • The half-life of 4,000 hours (phosphorus begins to degrade after)
  • Requires DC to AC convertor

Considering the limited life span of this backlighting solution and the price point of this mature technology, it is a viable solution in a few unique cases.

To see how electroluminescent lighting works, watch our short video below.