QMK has the ability to control RGB LEDs attached to your keyboard. This is commonly called *underglow*, due to the LEDs often being mounted on the bottom of the keyboard, producing a nice diffused effect when combined with a translucent case.
Some keyboards come with RGB LEDs preinstalled. Others must have them installed after the fact. See the [Hardware Modification](#hardware-modification) section for information on adding RGB lighting to your keyboard.
These LEDs are called "addressable" because instead of using a wire per color, each LED contains a small microchip that understands a special protocol sent over a single wire. The chip passes on the remaining data to the next LED, allowing them to be chained together. In this way, you can easily control the color of the individual LEDs.
At minimum you must define the data pin your LED strip is connected to, and the number of LEDs in the strip, in your `config.h`. If your keyboard has onboard RGB LEDs, and you are simply creating a keymap, you usually won't need to modify these.
QMK uses [Hue, Saturation, and Value](https://en.wikipedia.org/wiki/HSL_and_HSV) to select colors rather than RGB. The color wheel below demonstrates how this works.
Note: For versions older than 0.6.117, The mode numbers were written directly. In `quantum/rgblight.h` there is a contrast table between the old mode number and the current symbol.
Use these defines to add or remove animations from the firmware. When you are running low on flash space, it can be helpful to disable animations you are not using.
By including `#define RGBLIGHT_LAYERS` in your `config.h` file you can enable lighting layers. These make
it easy to use your underglow LEDs as status indicators to show which keyboard layer is currently active, or the state of caps lock, all without disrupting any animations. [Here's a video](https://youtu.be/uLGE1epbmdY) showing an example of what you can do.
To define a layer, we modify `keymap.c` to list out LED ranges and the colors we want to overlay on them using an array of `rgblight_segment_t` using the `RGBLIGHT_LAYER_SEGMENTS` macro. We can define multiple layers and enable/disable them independently:
```c
// Light LEDs 6 to 9 and 12 to 15 red when caps lock is active. Hard to ignore!
We combine these layers into an array using the `RGBLIGHT_LAYERS_LIST` macro, and assign it to the `rgblight_layers` variable during keyboard setup. Note that you can only define up to 8 lighting layers. Any extra layers will be ignored. Since the different lighting layers overlap, the order matters in the array, with later layers taking precedence:
```c
// Now define the array of layers. Later layers take precedence
If you need to change your RGB lighting in code, for example in a macro to change the color whenever you switch layers, QMK provides a set of functions to assist you. See [`rgblight.h`](https://github.com/qmk/qmk_firmware/blob/master/quantum/rgblight.h) for the full list, but the most commonly used functions include:
|`rgblight_setrgb_at(r, g, b, index)` |Set a single LED to the given RGB value, where `r`/`g`/`b` are between 0 and 255 and `index` is between 0 and `RGBLED_NUM` (not written to EEPROM) |
|`rgblight_sethsv_at(h, s, v, index)` |Set a single LED to the given HSV value, where `h`/`s`/`v` are between 0 and 255, and `index` is between 0 and `RGBLED_NUM` (not written to EEPROM) |
|`rgblight_setrgb_range(r, g, b, start, end)`|Set a continuous range of LEDs to the given RGB value, where `r`/`g`/`b` are between 0 and 255 and `start`(included) and `stop`(excluded) are between 0 and `RGBLED_NUM` (not written to EEPROM)|
|`rgblight_sethsv_range(h, s, v, start, end)`|Set a continuous range of LEDs to the given HSV value, where `h`/`s`/`v` are between 0 and 255, and `start`(included) and `stop`(excluded) are between 0 and `RGBLED_NUM` (not written to EEPROM)|
|`rgblight_setrgb(r, g, b)` |Set effect range LEDs to the given RGB value where `r`/`g`/`b` are between 0 and 255 (not written to EEPROM) |
|`rgblight_setrgb_master(r, g, b)` |Set the LEDs on the master side to the given RGB value, where `r`/`g`/`b` are between 0 and 255 (not written to EEPROM) |
|`rgblight_setrgb_slave(r, g, b)` |Set the LEDs on the slave side to the given RGB value, where `r`/`g`/`b` are between 0 and 255 (not written to EEPROM) |
|`rgblight_sethsv_master(h, s, v)` |Set the LEDs on the master side to the given HSV value, where `h`/`s`/`v` are between 0 and 255 (not written to EEPROM) |
|`rgblight_sethsv_slave(h, s, v)` |Set the LEDs on the slave side to the given HSV value, where `h`/`s`/`v` are between 0 and 255 (not written to EEPROM) |
Example:
```c
rgblight_sethsv(HSV_WHITE, 0); // led 0
rgblight_sethsv(HSV_RED, 1); // led 1
rgblight_sethsv(HSV_GREEN, 2); // led 2
// The above functions automatically calls rgblight_set(), so there is no need to call it explicitly.
// Note that it is inefficient to call repeatedly.
If you want to make the logical order of LEDs different from the electrical connection order, you can do this by defining the `RGBLIGHT_LED_MAP` macro in your `config.h`.
Using the `rgblight_set_clipping_range()` function, you can prepare more buffers than the actual number of LEDs, and output some of the buffers to the LEDs. This is useful if you want the split keyboard to treat left and right LEDs as logically contiguous.
You can set the Clipping Range by executing the following code.
If your keyboard lacks onboard underglow LEDs, you may often be able to solder on an RGB LED strip yourself. You will need to find an unused pin to wire to the data pin of your LED strip. Some keyboards may break out unused pins from the MCU to make soldering easier. The other two pins, VCC and GND, must also be connected to the appropriate power pins.
