Fix ESPHome color temperature precision for light entities (#91424)

Co-authored-by: J. Nick Koston <nick@koston.org>

homeassistant/components/esphome/light.py

@@ -13,7 +13,7 @@ from aioesphomeapi import (
 
 from homeassistant.components.light import (
     ATTR_BRIGHTNESS,
-    ATTR_COLOR_TEMP,
+    ATTR_COLOR_TEMP_KELVIN,
     ATTR_EFFECT,
     ATTR_FLASH,
     ATTR_RGB_COLOR,
@@ -98,6 +98,20 @@ _COLOR_MODE_MAPPING = {
 }
 
 
+def _mired_to_kelvin(mired_temperature: float) -> int:
+    """Convert absolute mired shift to degrees kelvin.
+
+    This function rounds the converted value instead of flooring the value as
+    is done in homeassistant.util.color.color_temperature_mired_to_kelvin().
+
+    If the value of mired_temperature is less than or equal to zero, return
+    the original value to avoid a divide by zero.
+    """
+    if mired_temperature <= 0:
+        return round(mired_temperature)
+    return round(1000000 / mired_temperature)
+
+
 def _color_mode_to_ha(mode: int) -> str:
     """Convert an esphome color mode to a HA color mode constant.
 
@@ -198,8 +212,9 @@ class EsphomeLight(EsphomeEntity[LightInfo, LightState], LightEntity):
                 # need to convert cw+ww part to white+color_temp
                 white = data["white"] = max(cw, ww)
                 if white != 0:
-                    min_ct = self.min_mireds
-                    max_ct = self.max_mireds
+                    static_info = self._static_info
+                    min_ct = static_info.min_mireds
+                    max_ct = static_info.max_mireds
                     ct_ratio = ww / (cw + ww)
                     data["color_temperature"] = min_ct + ct_ratio * (max_ct - min_ct)
                 color_modes = _filter_color_modes(
@@ -216,8 +231,9 @@ class EsphomeLight(EsphomeEntity[LightInfo, LightState], LightEntity):
         if (transition := kwargs.get(ATTR_TRANSITION)) is not None:
             data["transition_length"] = transition
 
-        if (color_temp := kwargs.get(ATTR_COLOR_TEMP)) is not None:
-            data["color_temperature"] = color_temp
+        if (color_temp_k := kwargs.get(ATTR_COLOR_TEMP_KELVIN)) is not None:
+            # Do not use kelvin_to_mired here to prevent precision loss
+            data["color_temperature"] = 1000000.0 / color_temp_k
             if _filter_color_modes(color_modes, LightColorCapability.COLOR_TEMPERATURE):
                 color_modes = _filter_color_modes(
                     color_modes, LightColorCapability.COLOR_TEMPERATURE
@@ -349,6 +365,12 @@ class EsphomeLight(EsphomeEntity[LightInfo, LightState], LightEntity):
         """Return the CT color value in mireds."""
         return round(self._state.color_temperature)
 
+    @property
+    @esphome_state_property
+    def color_temp_kelvin(self) -> int:
+        """Return the CT color value in Kelvin."""
+        return _mired_to_kelvin(self._state.color_temperature)
+
     @property
     @esphome_state_property
     def effect(self) -> str | None:
@@ -385,3 +407,6 @@ class EsphomeLight(EsphomeEntity[LightInfo, LightState], LightEntity):
         self._attr_effect_list = static_info.effects
         self._attr_min_mireds = round(static_info.min_mireds)
         self._attr_max_mireds = round(static_info.max_mireds)
+        if ColorMode.COLOR_TEMP in supported:
+            self._attr_min_color_temp_kelvin = _mired_to_kelvin(static_info.max_mireds)
+            self._attr_max_color_temp_kelvin = _mired_to_kelvin(static_info.min_mireds)

tests/components/esphome/test_light.py

@@ -76,8 +76,8 @@ async def test_light_color_temp(
             key=1,
             name="my light",
             unique_id="my_light",
-            min_mireds=153,
-            max_mireds=400,
+            min_mireds=153.846161,
+            max_mireds=370.370361,
             supported_color_modes=[
                 LightColorCapability.COLOR_TEMPERATURE
                 | LightColorCapability.ON_OFF
@@ -90,7 +90,7 @@ async def test_light_color_temp(
             key=1,
             state=True,
             brightness=100,
-            color_temperature=153,
+            color_temperature=153.846161,
             color_mode=LightColorCapability.COLOR_TEMPERATURE,
         )
     ]
@@ -106,10 +106,93 @@ async def test_light_color_temp(
     assert state.state == STATE_ON
     attributes = state.attributes
 
-    assert attributes[ATTR_MAX_MIREDS] == 400
     assert attributes[ATTR_MIN_MIREDS] == 153
-    assert attributes[ATTR_MIN_COLOR_TEMP_KELVIN] == 2500
-    assert attributes[ATTR_MAX_COLOR_TEMP_KELVIN] == 6535
+    assert attributes[ATTR_MAX_MIREDS] == 370
+
+    assert attributes[ATTR_MIN_COLOR_TEMP_KELVIN] == 2700
+    assert attributes[ATTR_MAX_COLOR_TEMP_KELVIN] == 6500
+    await hass.services.async_call(
+        LIGHT_DOMAIN,
+        SERVICE_TURN_ON,
+        {ATTR_ENTITY_ID: "light.test_my_light"},
+        blocking=True,
+    )
+    mock_client.light_command.assert_has_calls(
+        [
+            call(
+                key=1,
+                state=True,
+                color_mode=LightColorCapability.COLOR_TEMPERATURE
+                | LightColorCapability.ON_OFF
+                | LightColorCapability.BRIGHTNESS,
+            )
+        ]
+    )
+    mock_client.light_command.reset_mock()
+
+    await hass.services.async_call(
+        LIGHT_DOMAIN,
+        SERVICE_TURN_OFF,
+        {ATTR_ENTITY_ID: "light.test_my_light"},
+        blocking=True,
+    )
+    mock_client.light_command.assert_has_calls([call(key=1, state=False)])
+    mock_client.light_command.reset_mock()
+
+
+async def test_light_color_temp_legacy(
+    hass: HomeAssistant, mock_client: APIClient, mock_generic_device_entry
+) -> None:
+    """Test a legacy light entity that does supports color temp."""
+    mock_client.api_version = APIVersion(1, 7)
+    entity_info = [
+        LightInfo(
+            object_id="mylight",
+            key=1,
+            name="my light",
+            unique_id="my_light",
+            min_mireds=153.846161,
+            max_mireds=370.370361,
+            supported_color_modes=[
+                LightColorCapability.COLOR_TEMPERATURE
+                | LightColorCapability.ON_OFF
+                | LightColorCapability.BRIGHTNESS
+            ],
+            legacy_supports_brightness=True,
+            legacy_supports_color_temperature=True,
+        )
+    ]
+    states = [
+        LightState(
+            key=1,
+            state=True,
+            brightness=100,
+            red=1,
+            green=1,
+            blue=1,
+            white=1,
+            cold_white=1,
+            color_temperature=153.846161,
+            color_mode=19,
+        )
+    ]
+    user_service = []
+    await mock_generic_device_entry(
+        mock_client=mock_client,
+        entity_info=entity_info,
+        user_service=user_service,
+        states=states,
+    )
+    state = hass.states.get("light.test_my_light")
+    assert state is not None
+    assert state.state == STATE_ON
+    attributes = state.attributes
+
+    assert attributes[ATTR_MIN_MIREDS] == 153
+    assert attributes[ATTR_MAX_MIREDS] == 370
+
+    assert attributes[ATTR_MIN_COLOR_TEMP_KELVIN] == 2700
+    assert attributes[ATTR_MAX_COLOR_TEMP_KELVIN] == 6500
     await hass.services.async_call(
         LIGHT_DOMAIN,
         SERVICE_TURN_ON,