Description a switch is a switch, and an led is an led, but this led illuminated button is abination of both! it's a medium sized button, large enough to press easily but not too big that it gets in the way of your project panel. It has a built in led that can be controlled separately from the switch action - either to indicate or just to look good. The body is a black plastic with the led built inside. There are two contacts for the button and two contacts for the led, one marked + and one -. The forward voltage of the led is about 3v so connect a 220 to 1000 ohm resistor in series just as you would with any other led to your 3v or higher power supply. This particular button has a blue body and led and is latching on/off. The two switch contacts are either connected or disconnected. When you push the button they will switch from one to the other, like an on-off switch. The led is separated from the button, so you can make it light up when on, light up when off, always lit, etc.