Integrating Light Guide Film Backlighting

CSI Keyboards is a global leader in membrane switch backlighting and interface backlighting technology. CSI has over 35 years of experiencing backlighting user interfaces, from as simple as backlighting a logo to backlighting individual keys to backlighting the entire interface surface. CSI’s backlit products include: backlit human machine interfaces, backlit membrane switches, backlit elastomeric keypads and backlit panels or signage.

Why Light Guide Film?

CSI integrates Light Guide Film (or LGF) into many of our backlit keypad interfaces and membrane switches. Light Guide Film is a thin film that will direct light produced by side-firing, or right-angle, LEDs across the area that needs to be backlit. The film is placed directly below the graphic overlay and above the circuit layer so that the light will not be obstructed by any circuit traces or tactile components. This film can be cut into any pattern or shape within your switch. Multiple LGF films can also be used within one application to provide discrete backlighting to different graphic features. Different colored LEDs can be used to achieve unique lighting effects or white LEDs can be used to light different printed graphics on the overlay.

It is critical that the LEDs are properly placed on the circuit in order to adequately light the intended area. CSI will carefully evaluate the placement of these LEDs to ensure adequate light distribution and to avoid any hot spots.  

There was a time when the only way to backlight interfaces was to use standalone LEDs or EL panels. The problem with using LEDs without LGF is the creation of hot spots and uneven dispersion of light. EL panels are not only expensive, but they are not as bright as today’s LEDs. LGF is extremely thin so it can be incorporated into membrane switches that can’t exceed a certain thickness.  It can provide even backlighting across large and small areas, and for applications where the light remains on while the switch is powered.

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