Illumination of User Interfaces
Within our technology division, in this section we are concerned with the possibilities to illuminate user interfaces. The reason for the necessity of such a technology is not always necessarily a badly lit work environment. In fact, lighting elements can also be used for signal function.
In the following paragraphs, the most frequent and efficient methods for the illumination of user interfaces are described.
At this method the corresponding lighting element is directly integrated into the button. In most cases a LED with a life of approx. 50.000 hours is used for that purpose, which is available in different colours. The transparency of the surface material for industrial keyboards permits to illuminate the keys efficiently. Foil as well as silicone as a surface material can be backlit because of the partial transparency of these materials. As "light-emitting" buttons, short-stroke or long-travel keys may be used. This method offers the advantage that no setup costs arise because the buttons can be conventionally assembled on the PCB without additional effort.
For this technology, the LEDs’ structure is not coupled to the button. They are either next to the buttons, below the buttons or placed position-independent as a signal indicator (e.g. Caps-Lock key). Latter is the more frequent function in this technology. In most cases for this purpose On/Off modes are realized visually. "Stand-Alone LEDs" also may be used for a direct lighting of the keys without being integrated into the corresponding keys. On silicone keyboards, for example, they are arranged without mechanical circuit elements directly below the button. Metal domes also can be illuminated by that way without the LED being integrated into these domes, but being fixed below the button.
This interesting form of illumination is based on the effect that on connecting to AC voltage energy is dissipated into light (electroluminescence). By that way the whole "EL foil" under the proper keypad/decor foil can be illuminated. All spaces without foil are not being illuminated. This permits the realization of user surface illumination nearly independent from the layout. In contrast to the utilization of LEDs, one-off costs are arising in this case because of the required individual adjustments. Though, the half life of the luminance is not as high as for other technologies. After 10.000 hours the luminance is about the half of the original one.
At first, a LED is used as luminous source, too. However, in contrast to other technologies, the light is emitted into plastic light guides. These light guides are roughened by chemical processes so that light is emitted there. This so-called Fibrelight method is manifold applicable; due to the light dispersion and the individual length of the light guides, user interfaces of all sizes can be backlit. By reason of the corresponding specific modification, set-up costs are arising for this method.
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left: Fibrelight technology
right: EL foils