Not too long ago, the only illumination option for switch manufacturers offering lighted switches was incandescent bulbs. As in most other applications, the limitations of incandescent bulbs are shorter life spans, higher levels of failure, and increased heat concerns. Of course, continually replacing bulbs in switches became not only a nuisance, but costly. High levels of failure created the demand to design switches so bulbs could be field replaceable from the front panel. Heat was always a concern if switches were to be illuminated for longer periods of time. At times, too much heat would cause switch caps to expand or contract so much they would fall off.
Another obvious drawback to incandescent bulbs is the lack of color. The only way to achieve a color from an illuminated switch with incandescent bulbs is to place a colored cap (or filter) over the bulb. Although many colors can be accomplished this way, control panels became "cluttered" with too many colors. Since colored caps had to be placed over incandescent bulbs, even in the off state, switches appeared with color.
As LED efficiencies steadily improved during the 1980's, illuminated switch manufacturers began to incorporate red, green, and amber LEDs, which increased the life span of switch illumination, greatly reduced the number of failures in the field, and reduced concerns of heat generation. In addition, it provided a much cleaner and more uniform look for the control panels. When a switch is in the off state, all switches (through use of a white diffuser and clear cap) appear white, providing a much cleaner look in the off condition.
During the 1990s, as blue and white LEDs began to emerge, switch manufacturers were quick to adopt these colors into their product mix as well. However, with the advent and refinement of the blue LED, the idea of mixing red, green, and blue together to achieve an entire spectrum of color captured the imagination. As the RGB phenomenon swept the electronics industry, switch manufacturers were faced with a somewhat unique challenge. The amount of area available to place an RGB LED inside of a switch was extremely limited. In addition, no off-the-shelf RGB packages were available for use inside products like switches.
Two of the biggest challenges faced by switch manufacturers are the amount of space available inside a switch and the number of terminals protruding from the base of a switch necessary to drive LEDs. To date, nearly all illuminated switches are limited to two LEDs per switch. Generally, the two colors offered are red and green. This combination provides users with three different colors red, green, and amber.
However, switch manufacturers like NKK Switches have developed new, cost-effective ways to incorporate RGB technology into switches. Key to the success of RGB illumination in switches is the quality of red, green, and blue LEDs used in the packaging.
To achieve optimal results, each of the primary-colored LEDs is screened and sorted based on nanometer (NM) and millicandela (MCD) ranges prior to packaging. Only the most favorable ranges of NM and MCD are considered in order to achieve the best colors when mixing. Individual colors for red, green and blue must not fall too far one way on the NM or MCD scales, or colors will become skewed when mixing. Since many switches are often used on a single control panel, the need for uniform color matching across the entire panel is important. Therefore, the need to select only the best LEDs is critical to the manufacturing process. Manufacturers such as NKK Switches have even gone as far as to effectively match RGB white. Previously thought to be unachievable, NKK ensures users that the mix of RGB white is consistent from one switch to the next.
Only those LEDs screened and sorted for optimal ranges are used for packaging on PC-boards. Small PC-boards, for some models as small as 3.0 mm x 3.0 mm, are created to hold each of the LEDs. These PC-boards are not only designed to fit into the switch base, but also for optimal spacing between LEDs. However, the overall area available for the three LEDs raises several challenges for switch manufacturers. Not only is the spacing between diodes important, but overall packaging must fit into the switch body. Often times, by manipulating the spacing between the LEDs, the color hue and mixing characteristics can change. Finding the perfect balance between LED package size and spacing between diodes can determine the overall quality of the end product.
Following the layout, lead wires are connected from the LEDs to PC-board, and are then placed into a housing unit, which is filled with a clear resin to protect the LEDs. The complete housing unit is fitted with terminals and ready for integration into the switch body.
The switch body undergoes a completely separate process. Prior to manufacturing, several switch prototypes are pre-designed to determine the optimum shape. Manufacturers must consider how far the LEDs should be placed from the bottom of the switch cap; how to integrate the LED package into the switch body, and how to connect the LED terminals protruding from the base of the switch to the LED diodes in the packaging. While at the same time, designing switches with the most aesthetic appeal.
The process to create RGB illumination for a switch is far from a simple or standard routine. On the contrary, it is safe to say every new RGB switch introduced to the market will be new designs. There is little opportunity to retrofit existing switch designs to accept a RGB LED solution. Rather, as new switches are introduced to the market, manufacturers will need to develop a new LED package, and new switch body for each new product offering. As a result, new tooling and new manufacturing processes will have to be developed and implemented to produce and assemble a final product.
Although switch manufacturers are developing innovative ways to bring RGB products to market, RGB availability is still relatively limited. Because of the high level of investment and effort required to create one RGB product, it's unlikely that there will be a broad range of RGB solutions available in the very near future.
However, depending on how this new innovation is received by OEMs, the rate of acceptance may be higher than anyone expects.
Jeff Kroening is a product development manager for NKK Switches.