A backlit keyboard is a keyboard where the keys are illuminated for viewing in dim or completely dark conditions. Backlighting is a common feature among the PC gamer market of keyboards due to their practicality in low light environments and for aesthetics.
Traditional Cherry MX and linear Alps SKCL series switches (including some Alps clones) support integrated LEDs within the shell of the switch itself. Each key is lit individually, and in some cases the power, intensity and even colour of each LED can be controlled independently.
The chief disadvantage with Cherry MX–based keyboards in particular has always been that the LED illuminates only part of the keycap. This results in either unevenly lit legends or a cramped legend layout to get all the glyphs on each keycap within the focused area of illumination. Cherry have introduced new switch variants to address this limitation.
The new Matias switch has a transparent polycarbonate shell to permit internal lighting within an Alps SKCL-style switch, whose complex internals do not permit both an LED and a click or tactile leaf. The whole switch is then lit from below, and the shell spreads out the light evenly.
Cherry subsequently introduced "RGB" versions of their Cherry MX switch family, which replace the LED recess with a lens designed to focus the light from a surface-mount RGB LED. The switch shell is again transparent, to allow the light from the LED to more evenly illuminate the keycap legend.
Traditional LEDs are monochromatic and have two legs: positive and negative. Keyboard switches designed to accept LEDs typically only provide space for a standard LED with two legs, so full-colour illumination is not possible. As stated above, Cherry themselves resolved this issue by providing support for external LEDs. Since the Cherry MX shell theoretically has space for a full RGB LED, clone manufacturers typically utilise all four base holes (two for the LED, and two for the jumper or diode) to accommodate the four legs of an RGB LED. The LED recess shape is amended to support such an LED, and RGB switches can be distinguished from monochrome LED switches by the shape of the LED recess.