@@ -73,9 +73,14 @@ async def set_brightness(
         ) is not None and light_effect.is_active:
             return await light_effect.set_brightness(brightness)
 
-        return await self.call(
-            "set_device_info", {"brightness": brightness, "device_on": True}
-        )
+        # Only re-assert device_on when the device is already on. This fixes a
+        # "zombie state" on some devices (e.g. Tapo L900-5) where set_device_info
+        # silently no-ops the LEDs without an explicit power state, while still
+        # allowing brightness to be changed on an off device without turning it on.
+        params: dict = {"brightness": brightness}
+        if self._device.is_on:
+            params["device_on"] = True
+        return await self.call("set_device_info", params)
 
     async def _check_supported(self) -> bool:
         """Additional check to see if the module is supported by the device."""
 
@@ -91,10 +91,12 @@ async def set_hsv(
             "color_temp": 0,  # If set, color_temp takes precedence over hue&sat
             "hue": hue,
             "saturation": saturation,
-            "device_on": True,
         }
         # The device errors on invalid brightness values.
         if value is not None:
             request_payload["brightness"] = value
+        # Only re-assert device_on when the device is already on; see Brightness.
+        if self._device.is_on:
+            request_payload["device_on"] = True
 
         return await self.call("set_device_info", {**request_payload})
@@ -65,9 +65,12 @@ async def set_color_temp(self, temp: int, *, brightness: int | None = None) -> d
                     *valid_temperature_range, temp
                 )
             )
-        params: dict = {"color_temp": temp, "device_on": True}
+        params: dict = {"color_temp": temp}
         if brightness:
             params["brightness"] = brightness
+        # Only re-assert device_on when the device is already on; see Brightness.
+        if self._device.is_on:
+            params["device_on"] = True
         return await self.call("set_device_info", params)
 
     async def _check_supported(self) -> bool:
 
@@ -0,0 +1,102 @@
+"""Tests that set_brightness/set_color_temp/set_hsv inject device_on correctly.
+
+Regression coverage for two interacting concerns:
+
+* Tapo L900-5 "zombie state" — device reports on but LEDs stay off unless
+  device_on is re-asserted in the set_device_info payload.
+* Issue #1532 — users want to change brightness on an already-off device
+  without turning it on as a side-effect.
+
+The compromise: re-assert device_on=True only when the device is currently on,
+otherwise leave it out so an off device stays off.
+"""
+
+from __future__ import annotations
+
+import pytest
+from pytest_mock import MockerFixture
+
+from kasa import Module
+from kasa.smart import SmartDevice
+
+from ...device_fixtures import get_parent_and_child_modules, parametrize
+
+brightness_smart = parametrize(
+    "has brightness", component_filter="brightness", protocol_filter={"SMART"}
+)
+color_smart = parametrize(
+    "has color", component_filter="color", protocol_filter={"SMART"}
+)
+color_temp_smart = parametrize(
+    "has color temperature",
+    component_filter="color_temperature",
+    protocol_filter={"SMART"},
+)
+
+
+@brightness_smart
+@pytest.mark.parametrize("is_on", [True, False])
+async def test_set_brightness_device_on_payload(
+    dev: SmartDevice, is_on: bool, mocker: MockerFixture
+) -> None:
+    brightness = next(get_parent_and_child_modules(dev, Module.Brightness))
+    owner = brightness._device
+    # Bypass any active light effect so set_brightness hits set_device_info.
+    if (effect := owner.modules.get(Module.SmartLightEffect)) is not None:
+        mocker.patch.object(
+            type(effect),
+            "is_active",
+            new_callable=mocker.PropertyMock,
+            return_value=False,
+        )
+
+    owner._info["device_on"] = is_on
+    mock_call = mocker.patch.object(brightness, "call")
+
+    await brightness.set_brightness(50)
+
+    expected: dict = {"brightness": 50}
+    if is_on:
+        expected["device_on"] = True
+    mock_call.assert_called_once_with("set_device_info", expected)
+
+
+@color_temp_smart
+@pytest.mark.parametrize("is_on", [True, False])
+async def test_set_color_temp_device_on_payload(
+    dev: SmartDevice, is_on: bool, mocker: MockerFixture
+) -> None:
+    ct = next(get_parent_and_child_modules(dev, Module.ColorTemperature), None)
+    if ct is None:
+        pytest.skip("Device has color_temperature component but no module enabled")
+    if ct.valid_temperature_range.min == ct.valid_temperature_range.max:
+        pytest.skip("Device exposes color_temperature but no usable range")
+
+    ct._device._info["device_on"] = is_on
+    mock_call = mocker.patch.object(ct, "call")
+
+    temp = ct.valid_temperature_range.min
+    await ct.set_color_temp(temp)
+
+    expected: dict = {"color_temp": temp}
+    if is_on:
+        expected["device_on"] = True
+    mock_call.assert_called_once_with("set_device_info", expected)
+
+
+@color_smart
+@pytest.mark.parametrize("is_on", [True, False])
+async def test_set_hsv_device_on_payload(
+    dev: SmartDevice, is_on: bool, mocker: MockerFixture
+) -> None:
+    color = next(get_parent_and_child_modules(dev, Module.Color))
+
+    color._device._info["device_on"] = is_on
+    mock_call = mocker.patch.object(color, "call")
+
+    await color.set_hsv(120, 50)
+
+    expected: dict = {"color_temp": 0, "hue": 120, "saturation": 50}
+    if is_on:
+        expected["device_on"] = True
+    mock_call.assert_called_once_with("set_device_info", expected)
@@ -67,6 +67,10 @@ async def test_light_effect_brightness(
     if effect_active:  # Set the rule L1 active for testing
         light_effect.data["current_rule_id"] = "L1"
 
+    # Force device_on so the asserted payload is deterministic across fixtures
+    # (some fixtures' get_device_info has device_on: false).
+    dev._info["device_on"] = True
+
     await light_module.set_brightness(10)
 
     if effect_active:
 
@@ -82,6 +82,10 @@ async def test_light_effect_brightness(
         return_value=effect_active,
     )
 
+    # Force device_on so the asserted payload is deterministic across fixtures
+    # (some fixtures' get_device_info has device_on: false).
+    dev._info["device_on"] = True
+
     await light_module.set_brightness(10)
 
     if effect_active:
Original file line number	Diff line number	Diff line change
@@ -65,9 +65,12 @@ async def set_color_temp(self, temp: int, *, brightness: int \| None = None) -> d
65	65	*valid_temperature_range, temp
66	66	)
67	67	)
68		- params: dict = {"color_temp": temp, "device_on": True}
	68	+ params: dict = {"color_temp": temp}
69	69	if brightness:
70	70	params["brightness"] = brightness
	71	+ # Only re-assert device_on when the device is already on; see Brightness.
	72	+ if self._device.is_on:
	73	+ params["device_on"] = True
71	74	return await self.call("set_device_info", params)
72	75
73	76	async def _check_supported(self) -> bool:
Original file line number	Diff line number	Diff line change
@@ -82,6 +82,10 @@ async def test_light_effect_brightness(
82	82	return_value=effect_active,
83	83	)
84	84
	85	+ # Force device_on so the asserted payload is deterministic across fixtures
	86	+ # (some fixtures' get_device_info has device_on: false).
	87	+ dev._info["device_on"] = True
	88	+
85	89	await light_module.set_brightness(10)
86	90
87	91	if effect_active: