What is a Backlighting Hot Spot and How to Prevent It

Backlighting on a membrane switch can be a simple and cost effective solution to enhance the user experience. Backlighting can tell the user the current machine status, and it can help walk the user through the next operation steps. That sounds great, so what could possibly go wrong? Have you ever heard of a hot spot? No, not the one on your phone that you can turn on to share your wifi – a backlighting hot spot. It’s when the light source used for backlighting doesn’t evenly distribute the light causing some areas to appear brighter (hot spot), while others are dimly lit. The switch will still work just the same, however, having the total package be reliable AND good looking, is critical for your brand and the end user experience.

Why do hot spots occur?

Evenly lighting a large graphic area with a tiny point light source like an LED can be problematic – the main issues are the size of the backlit area, how many LED’s can fit in the design, and how close the LED’s can be placed to the backlit feature. If you want to backlight a small icon, it is relatively easy to have a smooth, evenly lit appearance. The larger the backlit area, the more difficult it will be to light it evenly without the appearance of hot spots. This is especially true if there is not enough room to place multiple LED’s surrounding the backlit feature.

So what can I do to avoid hot spots?

A proper design is the key to avoiding hot spots. Most HMI (human machine interface) manufacturers would prefer to be involved in the design process rather than working to adjust it after the fact. The earlier in the process you can get them involved, the better:

• faster time to production – less rework and time spent in R&D to ensure the design will yield the desired results
• greater potential for cost savings – the right design, materials, and patterns used right away
• overall better product – why risk it?