When selecting an illuminated switch, it is important to understand that there is no definite relationship between the switch’s rated contact voltage(s) and the voltage required or appropriate for driving the illumination mechanism.
Most of the switch product families on the DigiKey website will have filters for AC and DC voltage ratings. These figures describe the voltage that a devices contacts are rated to interrupt, and have nothing to do with the voltage appropriate for driving a built-in light source.
A bit further over in the filter selections for switch families offering illumination options, one will usually find columns titled “Illumination Type, Color” and “Illumination Voltage (Nominal)” These attributes reflect the lighting technology used and give insight into the accommodations needed to drive them appropriately.
Incandescent light sources are simply miniature versions of traditional light bulbs, and behave the same way; connect them to a voltage source of the indicated nominal value, and they light up. More voltage results in more light and shorter service life, less voltage results in less light and a longer service life.
LED light sources are based on the use of indicator-class LEDs, and are driven like any other such device, most often through the use of an additional series resistor. A given switch may incorporate such a resistor or not, with the distinction recognizable on the basis of whether the illumination voltage is in the range typical for the forward voltage of a single LED (about 1.5 to 3V depending on color) or some higher value more typical of commonly-used voltage sources, e.g. 5V or more.
Neon illuminants are a form of gas discharge lamp that require a relatively high voltage to ignite and a series resistance to limit current flow once lit. That resistance is most often built in when incorporated into a switch, and devices that do so are most often used for switching AC utility power.
All device characteristics should be validated using the manufacturer’s documentation. Product information on the DigiKey website results from an ongoing aggregation process that is subject to error, and is not guaranteed.