diff --git a/custom_components/adaptive_lighting/color_and_brightness.py b/custom_components/adaptive_lighting/color_and_brightness.py
index c91278fc..5e1d8a75 100644
--- a/custom_components/adaptive_lighting/color_and_brightness.py
+++ b/custom_components/adaptive_lighting/color_and_brightness.py
@@ -528,5 +528,13 @@ def lerp(x: float, x1: float, x2: float, y1: float, y2: float) -> float:
 
 
 def clamp(value: float, minimum: float, maximum: float) -> float:
-    """Clamp value between minimum and maximum."""
-    return max(minimum, min(value, maximum))
+    """Clamp value between minimum and maximum.
+
+    `minimum` is not assumed to be <= `maximum`: a user may intentionally
+    configure `min_brightness > max_brightness` (or the equivalent for color
+    temperature) for an inverted timescale (#1421). Sort the bounds first so
+    that case clamps against the real lower/upper bound instead of
+    collapsing to `minimum` for every input.
+    """
+    low, high = (minimum, maximum) if minimum <= maximum else (maximum, minimum)
+    return max(low, min(value, high))
diff --git a/tests/test_color_and_brightness.py b/tests/test_color_and_brightness.py
index 32425055..86cec8a8 100644
--- a/tests/test_color_and_brightness.py
+++ b/tests/test_color_and_brightness.py
@@ -7,6 +7,8 @@ from astral.location import Location
 from homeassistant.components.adaptive_lighting.color_and_brightness import (
     SunEvent,
     SunEvents,
+    SunLightSettings,
+    clamp,
 )
 
 # Create a mock astral location object (its `.observer` is passed to `SunEvents`)
@@ -207,3 +209,91 @@ def test_closest_event(tzinfo_and_location):
     event_name, ts = sun_events.closest_event(sunrise)
     assert event_name == SunEvent.SUNRISE
     assert ts == location.sunrise(sunrise.date()).timestamp()
+
+
+def _make_brightness_settings(
+    tzinfo,
+    location,
+    *,
+    min_brightness,
+    max_brightness,
+    brightness_mode,
+):
+    """Build a SunLightSettings with only the fields brightness_pct() needs."""
+    return SunLightSettings(
+        name="test",
+        astral_observer=location.observer,
+        adapt_until_sleep=False,
+        max_brightness=max_brightness,
+        max_color_temp=6500,
+        min_brightness=min_brightness,
+        min_color_temp=2000,
+        sleep_brightness=1,
+        sleep_rgb_or_color_temp="color_temp",
+        sleep_color_temp=2000,
+        sleep_rgb_color=(255, 56, 0),
+        sunrise_time=None,
+        min_sunrise_time=None,
+        max_sunrise_time=None,
+        sunset_time=None,
+        min_sunset_time=None,
+        max_sunset_time=None,
+        brightness_mode_time_dark=dt.timedelta(minutes=30),
+        brightness_mode_time_light=dt.timedelta(minutes=30),
+        brightness_mode=brightness_mode,
+        timezone=tzinfo,
+    )
+
+
+def test_clamp_handles_inverted_bounds():
+    """A user can intentionally set min_brightness > max_brightness for an
+    inverted timescale (#1421, e.g. a porch light that should be brighter at
+    night than during the day). clamp() must still bound the value between
+    whichever of the two is actually smaller/larger, not silently collapse
+    to `minimum` for every input the way `max(minimum, min(value, maximum))`
+    does when minimum > maximum.
+    """
+    assert clamp(50, 100, 15) == 50
+    assert clamp(0, 100, 15) == 15
+    assert clamp(200, 100, 15) == 100
+
+
+def test_clamp_normal_bounds_unaffected():
+    """The ordinary min <= max case must keep behaving exactly as before."""
+    assert clamp(50, 0, 100) == 50
+    assert clamp(-10, 0, 100) == 0
+    assert clamp(150, 0, 100) == 100
+
+
+@pytest.mark.parametrize("brightness_mode", ["linear", "tanh"])
+def test_brightness_pct_varies_with_inverted_brightness_bounds(
+    tzinfo_and_location,
+    brightness_mode,
+):
+    """#1421: with min_brightness > max_brightness, linear/tanh modes got
+    stuck returning min_brightness for every sample, because the final
+    `clamp(brightness, self.min_brightness, self.max_brightness)` call
+    collapsed to `minimum` regardless of the computed value. Sampling a few
+    points around sunrise must show the brightness actually move instead of
+    being pinned to one value.
+    """
+    tzinfo, location = tzinfo_and_location
+    settings = _make_brightness_settings(
+        tzinfo,
+        location,
+        min_brightness=100,
+        max_brightness=15,
+        brightness_mode=brightness_mode,
+    )
+
+    sunrise = location.sunrise(dt.datetime(2022, 6, 1).date())
+    samples = [
+        settings.brightness_pct(
+            sunrise + dt.timedelta(minutes=offset),
+            is_sleep=False,
+        )
+        for offset in (-20, -10, 0, 10, 20)
+    ]
+
+    assert len({round(value) for value in samples}) > 1, samples
+    assert all(15 <= value <= 100 for value in samples), samples
diff --git a/tests/test_switch.py b/tests/test_switch.py
index a48800f2..37e9df38 100644
--- a/tests/test_switch.py
+++ b/tests/test_switch.py
@@ -1727,7 +1727,7 @@ async def test_change_switch_settings_service(hass):
     # Test changing to illegal max brightness
     with pytest.raises(
         voluptuous.error.MultipleInvalid,
-        match="value must be at most 100 for dictionary",
+        match="value must be at most 100",
     ):
         await change_switch_settings(**{CONF_MAX_BRIGHTNESS: 5000})