ESPHome Custom RGBW Light with emulated warm/cool white

frankeverCustomLight.h

#include "esphome.h"

class FrankeverCustomLight : public Component, public LightOutput {
  public:
  FrankeverCustomLight(FloatOutput *red, FloatOutput *green, FloatOutput *blue, FloatOutput *white)
  {
    red_ = red;
    green_ = green;
    blue_ = blue;
    white_ = white;
  }

  LightTraits get_traits() override {
    auto traits = LightTraits();
    traits.set_supports_brightness(true);
    traits.set_supports_rgb(true);
    traits.set_supports_rgb_white_value(false);
    traits.set_supports_color_temperature(true);
    traits.set_min_mireds(153); // home assistant minimum 153
    traits.set_max_mireds(500); // home assistant maximum 500
    // medium is 326.5
    return traits;
  }

  void write_state(LightState *state) override {
    float red, green, blue, cwhite, wwhite, colourTemp;
    state->current_values_as_rgbww(&red, &green, &blue, &cwhite, &wwhite);
    colourTemp = state->current_values.get_color_temperature();

    // TODO at the moment the lights boot up with cool temperature, can we default to warm?
    float coolToWarmThreshold = (colourTemp - 153) / (500 - 153);

    // slowly fade in white LED and fade out colour LEDs
    float whitePart = std::min(red, std::min(green, blue));
    float redPart = red - whitePart;
    float greenPart = green - whitePart;
    float bluePart = blue - whitePart;

    float whiteLightMultiplier = std::min(coolToWarmThreshold * 2.25f, 1.0f); // half way point is full white light, so turn 0.5 -> 1
    float colourLightMultiplier = std::max(-(coolToWarmThreshold * 2.25f - 1.0f), 0.0f);
    float extraRedMultiplier = whitePart * std::max(0.0f, std::min((coolToWarmThreshold - 0.6f) * 2.0f, 1.0f)); // beyond half way is extra warm red

    float newWhite = whitePart * whiteLightMultiplier;
    float newRed = (colourLightMultiplier * (red - redPart)) + redPart;
    float newGreen = (colourLightMultiplier * (green - greenPart)) + greenPart;
    float newBlue = (colourLightMultiplier * (blue - bluePart)) + bluePart;

    float newRedWithExtraRed = (extraRedMultiplier * (1 - newRed)) + newRed;

    // ESP_LOGD("custom",
    //   "colourTemp %f, whitepart %f redpart %f greenpart %f bluepart %f whitemulti %f colourmulti %f extramulti %f newwhite %f newred %f newgreen %f newblue %f newnewred %f",
    //   colourTemp, whitePart, redPart, greenPart, bluePart, whiteLightMultiplier, colourLightMultiplier, extraRedMultiplier, newWhite, newRed, newGreen, newBlue, newRedWithExtraRed);

    this->red_->set_level(newRedWithExtraRed);
    this->green_->set_level(newGreen);
    this->blue_->set_level(newBlue);
    this->white_->set_level(newWhite);
  }

  protected:
  FloatOutput *red_;
  FloatOutput *green_;
  FloatOutput *blue_;
  FloatOutput *white_;
};

light.yaml

esphome:
  includes:
    - frankeverCustomLight.h
    
output:
  - platform: my9231
    id: output_red
    channel: 3
  - platform: my9231
    id: output_green
    channel: 2
  - platform: my9231
    id: output_blue
    channel: 1
  - platform: my9231
    id: output_white
    channel: 0

light:
  - platform: custom
    lambda: |-
      auto light_out = new FrankeverCustomLight(id(output_red), id(output_green), id(output_blue), id(output_white));
      App.register_component(light_out);
      return {light_out};
    lights:
      - name: "${friendly_name}"
        default_transition_length: 0.1s
        restore_mode: ALWAYS_OFF # because powercut could then cause all lights to turn on
        effects:
          - random:
          - strobe:
          - flicker:

Jamie:

I have made some changes to your code: https://gist.github.com/triphoppingman/76153ddf58072b10e229e9147b2bdf72

This maps the color temp to the RGBW values using a set of linear equations.