How Illuminated Switches Work
This module will help to “illuminate” how illuminated switches work and their functions, as well as work to display a wide variety of the illuminated switches NKK offers. You can see more information about these products on the Illuminated Switches product page.
Types of Illumination
In switch illumination, there are several options depending on your application. NKK has found LED to be the most universally effective, but we will also discuss incandescent and neon illumination in this section.
LED switches feature a long life, in part due to the low current and DC voltage levels, but entail higher initial costs. They are not easily damaged by shock, though they require a ballast resistor. LEDs come in a variety of colors, including bicolor and RGB, and have Bright and Super Bright options.
Incandescent lamps have lower initial costs but have a shorter life compared to LEDs. These are also sensitive to shock and vibration, with high heat dissipation due to their brightness.
Neon lamps also have a lower life but are not easily damaged by shock or vibration. They have a lower intensity brightness and require a resistor.
LED Wires and Circuits
This example shows isolated circuits from an external source where the red and dark blue wires are soldered to an external source. This source will send the current that illuminates the lamp. The source current will depend upon the lamp specifications, and all of NKK’s switches come with isolated circuits for lamps.
For isolated circuits wires in line with switch actuation, the above shows a resistor wired to the positive lamp terminal from the “Normally Open” switch terminal. As a result, when the switch is actuated from the “Normally Closed” terminal to the “Normally Open” terminal, the lamp will illuminate. The resistor is required to properly power the lamp.
For an LED circuit, the illumination is created by the properties of the diode (Anode “+” and Cathode “-”). Once the Forward Voltage (Vf) and Current (If) are achieved, the LED will illuminate. If the voltage is reversed and exceeds the Reversed Voltage (Vr), the LED can be damaged. The ballast resistor (R) is used to create the proper voltage and current through the circuit. An alternative to the ballast resistor is a constant current source circuit.
The LED is generally used in DC applications. If an AC circuit is to be used, a rectifier circuit along the ballast resistor is required to generate the appropriate DC voltage.
Ballast Resistor Calculation
In order to calculate the ballast resistor value, the following formula should be used:
As an example, if the Source Voltage (E) is 5.0V, the Forward Voltage (Vf) is 1.9V (set by LED), and the Forward Current (If) is 20mA (set by LED), then the resultant ballast resistor is 155Ω.
R = (5.0V – 1.9V) / 20mA = 155Ω
Additionally, the power rating of the ballast resistor must be considered. With a forward current of 20mA and the voltage across the ballast resistor being 3.1V (5.0V – 1.9V), the power across is then calculated: 3.1V x 20mA = 0.062W. For safety purposes, the typical power rating is 2X the calculated value resulting in a power rating of 0.125W (¼ W resistor).
For an LED, forward voltages are different for each LED and color. In switches where bicolor or RGB LEDs are used, different ballast resistor values may be required for each LED. The current profile of an LED is that it varies with temperature, so the value of the ballast resistors should be calculated at the appropriate operating temperature using the current reduction rate information supplied below.
LED Colors and Chromaticity
NKK offers LED illuminated switches in single color, bicolor, RGB, and white. Single-color LEDs include red, green, amber, blue, and white. White is generated with either a blue LED and yellow fluorescent (analog white) or generated by RGB (digital white). Bicolor LED options include Red/Green (Amber when both are illuminated), Red/Yellow, Blue/Amber, or Clear or White in any combination of the above colors. Using RGB, any color apart from black can theoretically be created by combining Red/Green/Blue. LED colors are shown in the Chromaticity Graph by their respective X-Y coordinates.
NKK Illuminated Switches
NKK offers a wide product offering of illuminated switches including pushbuttons, alternating legends, tactiles, toggles, and many more, all shown below.
As seen with the alternating legends, NKK also excels in custom switch solutions and value added services. We have the flexibility, expertise, and skills to help engineers design custom switch solutions for today’s most innovative applications. We offer custom printing, including laser etching, screen printing, and pad printing, as well as custom assembly. Please reach out to our team at email@example.com for more information and design advice.
Illuminated switches are vital to the user experience of any application, and can be used in the following industries:
- Medical Equipment
- And many others!