Four Ways to Fix Backlight Bleed on Overlays

Posted by on Oct 29, 2018

Enhancements to Light Guide Technology Lead to Reduced Backlight Bleed on Graphic Overlays

Graphic overlays are a critical interface layer on many of the electronic devices we use today. Not only do they elevate common applications from a functional standpoint, but they communicate important visual information that, ultimately, impacts the end user experience.

While graphic overlays aren’t new, one common problem that continues to interfere with the quality of their performance is backlight bleed.

The Problem with Backlight Bleed

Think of backlight bleed as a light leak. When you add graphic overlays to devices, every icon within the overlay is individually lit by an LED bulb behind it. Ideally, when a user touches a single icon, it lights up whereas the rest of the screen remains dark.

The issue is that light wants to go everywhere, naturally. Often times, when a user pushes one icon on the screen, other icons will brighten because the LED light is spilling over into other sections of the screen.

Backlight bleed is more common in capacitive touch applications. Many of these devices contain graphic overlays that have multiple icons or buttons. Given the thinness of these applications and minimal space between the icons and LEDs behind them, uncontrolled light leaks across the overlay.

Related Content: Accelerating Capacitive Touch Design in Cars

While some minor backlight bleed is expected and even tolerable, it can also be way too apparent. Product manufacturers don’t want to cross that line. An abundance of backlight bleed can lead users to assume their devices are malfunctioning or even broken.

Reducing Backlight Bleed: Simple to Complex Light Guide Solutions

So how do we help our clients minimize backlight bleed when it rears its head? Over time, we’ve innovated our light guide design, adding different design features for better control. Each of these options allows us to maintain the overall thinness of the light guide itself, too.

  1. Cut out design – A cost-effective option for decreasing backlight bleed is making cuts (with our in-house lasers) directly into the light guides. These cutouts allow for better light blocking and control. While some light escapes the guide, it won’t spill over into unintended areas of the overlay. As you continue reading through the remaining solutions, you’ll notice that we’ve further enhanced the cutout design, adding new optical features to make it even more effective.
  2. Housing (with ribs) design – Building upon the cutout design, we’ve developed another solution that leverages white plastic housing with “ribs” or raised features that slide into the cutouts of the light guide. These housing ribs reflect light back into the light guide instead of letting it pass through any air gaps and into the neighboring section. The only negative to this option is that the plastic housing adds more weight to the light guide, so it’s not always ideal for ultra-thin applications.
  3. Foam design – We’ve also developed a light guide with cutouts, but instead of using housing ribs, we insert black poron foam to absorb escaping light. While this design is similar to a light guide with housing, the foam isn’t as bulky and our customers can maintain a thin assembly.
  4. Overmold design – A simple way of thinking about our overmold design is multiple small light guides, with cutouts, fused together with a plastic molding to block backlight bleed. This process allows for no additional components (housings or foam) to be added to the assembly while still blocking light bleed. While this option is highly effective, it does require additional mold tooling and design, making it more expensive.

So which light guide option is right for you? It all depends on your project requirements, volume and budget. We also use our optical software to simulate where backlight bleed may occur within a given graphic overlay, helping us identify which option will deliver the absolute best results.

Do you need help controlling backlight bleed or another custom lighting solution? Contact our lighting experts today.

We bet you have a bright idea.
Let’s see how GLT can help make it a reality.

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