How to Prevent Hot Spots in Membrane Switches

A common issue that many membrane switch manufacturers have when backlighting keypads are hot spots. A hot spot occurs when the light source used for backlighting doesn’t evenly distribute the light causing some areas to appear brighter (hot spot), while other areas are dimly lit. 

CSI Keyboards is a global leader in membrane switch backlighting and interface backlighting technology. Whether backlighting a logo, individual keys, or the entire interface surface, CSI will design and manufacture a backlit membrane keypad switches or backlit interface that will stand out both visually and aesthetically. Backlighting on a membrane switch can be a simple and cost effective solution to enhance the user experience.  

Evenly lighting a large area with a small light source like an LED can be challenging. The main challenges are the size of the backlit area, the amount of LED’s that can fit in the area, and the proximity of the LED’s to the backlit feature. Backlighting a small icon can be relatively easy, but the larger the backlit area, the more difficult it will be to evenly light the graphic 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.

How to Avoid Hot Spots

CSI Keyboards is an expert and integrating Light Guide Film (LGF) into our backlit solutions to prevent hot spots from occurring. Light Guide Film is designed to evenly distribute light from top or side firing LEDs, providing bright, uniformed illumination. It also reduces the amount of LEDs needed, saving power consumption. More on light guide film technology below. The design and utilization of light guide film technology has become one of the most common methods of interface backlighting. CSI Keyboards uses proprietary techniques to design the light guide film so it is optimized for light redirection and reflection giving the customer the brightest possible backlighting solution. Light guide film dots are also designed and implemented which allow for the optimization of light distribution to obtain maximum brightness and uniformity. Common problems that many of our competitors face are light leakage and hot spots. CSI’s backlighting designs prevent any light leakage and hot spots from occurring, and also result in much brighter light guide film and interface.

It’s always important to remember that the earlier CSI is involved in the design process the better. It’s a lot more difficult completely redesigning the backlighting layout, versus ensuring it is right from the onset of the design process!

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