Illumination - reliable operation in the dark

Let there be light! Work stations in low light conditions such as traffic engineering or medical technology require keyboards that are illuminated internally. The illuminated membrane keyboards with electroluminescent technology by Hoffmann + Krippner have proven reliable over time.

LED technology combined with a sophisticated structure allows the implementation of illuminated membrane switches only slightly thicker than the popular EL lighting. Long life cycles, high brightness and the option for individual control buttons allow for completely new application areas.

A common method for illuminating membrane switches is the use of EL films. With a flat design, low power consumption, and a very homogeneous light emission, the EL film is fundamentally suited for this purpose. On the other hand, due to the relatively short life - depending on control voltage, half life < 10'000h -, a rather moderate brightness as well as the need for special control voltage (110 VAC, 400 Hz) this technology is rather limited.

An alternative frequently used are tactile switches with illuminated LED domes. However, this solution requires a complex and space-intensive construction, consisting of a printed circuit board with buttons as well as a precisely mounted carrier for the front foil. In addition to the high cost, this method presents challenges regarding the precisely mounted front panel required for flawless functionality.

The new method used by Hoffmann + Krippner combines the advantages of two existing technologies. Therefore the LED technology is used, however, thanks to an ingenious design combining side LEDs with diffusing panels, only slightly more space than with the EL film is required. This allows the possibility to build a keyboard, less than 3mm in thickness, with illuminated buttons that are uniform, bright and long-lasting.

Optional light seperation between keys even allows to seperately illuminate each individual key. The use of bi-color or RGB LEDs also provides a virtually unlimited choice of colors. Since the structure must be placed on a circuit board, the unused space in the back provides space to mount a series of resistors and driver ICs, or even an entire customized electronic circuitry.

The advantages of this new technology open up completely new application possibilities for membrane switches. Further refinement of the design foil through embossing or GT-domes is still an option as well as the integration of resistive or capacitive touchscreens. This is how the touch operation can be enhanced through keys with visual and haptic perception. With a front foil laminated over the full-area display, IP protection also prevents dirt from collecting in any edges

Further benefits:

  • extremely flat, cold light source
  • ideal extension to membrane switches
  • even surface illumination of lettering on keyboard
  • wide range of brightness adjustments