Backlighting technologies: Discrete LEDs (part 2 of 5)

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By Steve Baker | Oct 08, 2020
Automotive panel with discrete LEDs

Last week we kickstarted a five-part blog series on backlighting technologies. Our first blog provides a framework to approach any new backlighting project and overcome design challenges. In this blog, we will be focusing on the first and the most popular backlighting technology – discrete LEDs.

Light-emitting diodes (LEDs), also referred to as discrete LEDs, are point-source lights that can be lit individually or in a group to illuminate a small area. Thanks to their low cost, thin construction, and long operating life, discrete LEDs have enjoyed widespread popularity and adoption across industries as diverse as medical, aerospace, automotive, and more.

Types of LEDs

LEDs come in different packages of varying shapes, sizes, types, and heights. The most commonly utilized types include surface-mount LEDs (top-fire or side-fire) and bullet LEDs. LED-backlit designs can be constructed in a range of colors and brightness levels. For example, a bi-colored LED as an indicator light turns green when the device is in use and the same light turns orange when the device is in standby mode.

In addition to the traditional single and bi-colored LEDs, RGB LEDs have opened doors to a wide gamut of colors and accent lighting options. RGB technology, combining three LEDs in a single package, mixes the three primary colors (red, green, and blue) in varying intensities to generate any color on the RGB spectrum. As a result, a single LED is capable of producing multiple colors.

LEDs are available in different correlated color temperature (CCT) values like the cool blues, warm yellows, and other tints. Whether you need dimmable, flashing, or non-flashing lights, LED designs can be composed in various styles. They can also be configured to light up all at once or selectively, as the design dictates. While surface-mount LEDs can either be mounted on a silver printed membrane, copper-etched flex circuit, or a printed circuit board with a connector that attaches to the mainboard, bullet LEDs can only be mounted on the latter two.

Advantages of LED backlighting

As point-sources of light, LEDs are great for small icons or indicator light applications, communicating the working or the status of the device. Some of the core advantages of discrete LEDs are:

  • Thin and robust construction
  • Limited impact on the tactile feel of buttons or snap domes
  • Long operating life (100,000 - 500,000+ hours)
  • Ability to illuminate the same area with different colors
  • Varying brightness level and color options
  • Cost-effective

Limitations with LED backlighting

LEDs usually struggle with lighting up large surfaces uniformly. A high count of LEDs in a concentrated area or placement of them close to a graphic overlay can create unwanted hotspots (bright areas) over or near the light source. Fortunately, both of these issues can be overcome by utilizing an elastomer keypad or overlay. Rubber overlays optimize light diffusion from LEDs, thereby mitigating hotspots and ensuring consistent brightness over the surface. A common challenge with elastomer is that it has a very different texture compared to a polycarbonate overlay and adds substantial thickness to the construction stack-up. Light dams or barricades often need to be incorporated in the design to overcome light bleed from one LED to the adjacent window. If you need to backlight a larger area and elastomer is not possible, you may want to consider a light guide film or fiber optic weave, which will be covered in our upcoming blogs.

To see a few examples of LED backlighting projects and learn more about this technology, watch our short video below.