diff --git a/Changes.md b/Changes.md
index d9545fc515c..e4bdc4a0024 100644
--- a/Changes.md
+++ b/Changes.md
@@ -5,6 +5,7 @@ Features
 --------
 
 - AttributeEditor, LightEditor, RenderPassEditor : Added drag and drop editing. Edits can be created or updated by dropping a value into a cell. Cells representing a set expression or string array can be modified by holding <kbd>Shift</kbd> to append to an existing edit, or <kbd>Control</kbd> may be held to remove from an existing edit.
+- USD : Added Cycles-specific light parameters to USD Lux lights.
 
 Fixes
 -----
diff --git a/src/GafferCycles/IECoreCyclesPreview/ShaderNetworkAlgo.cpp b/src/GafferCycles/IECoreCyclesPreview/ShaderNetworkAlgo.cpp
index 69e58fedd4a..1103b68bbb6 100644
--- a/src/GafferCycles/IECoreCyclesPreview/ShaderNetworkAlgo.cpp
+++ b/src/GafferCycles/IECoreCyclesPreview/ShaderNetworkAlgo.cpp
@@ -946,6 +946,8 @@ const InternedString g_widthParameter( "width" );
 const InternedString g_wrapSParameter( "wrapS" );
 const InternedString g_wrapTParameter( "wrapT" );
 
+const string g_cyclesNamespace( "cycles:" );
+
 void transferUSDLightParameters( ShaderNetwork *network, InternedString shaderHandle, const Shader *usdShader, Shader *shader )
 {
 	Color3f color = parameterValue( usdShader, g_colorParameter, Color3f( 1 ) );
@@ -967,6 +969,14 @@ void transferUSDLightParameters( ShaderNetwork *network, InternedString shaderHa
 	shader->parameters()[g_useGlossyParameter] = new BoolData( specular > 0.0f );
 
 	shader->parameters()[g_useMISParameter] = new BoolData( true );
+
+	for( const auto &[name, value] : usdShader->parameters() )
+	{
+		if( boost::starts_with( name.string(), g_cyclesNamespace ) )
+		{
+			shader->parameters()[name.string().substr(g_cyclesNamespace.size())] = value;
+		}
+	}
 }
 
 void transferUSDShapingParameters( ShaderNetwork *network, InternedString shaderHandle, const Shader *usdShader, Shader *shader )
diff --git a/startup/GafferUSD/cyclesLights.py b/startup/GafferUSD/cyclesLights.py
new file mode 100644
index 00000000000..8c0664affc5
--- /dev/null
+++ b/startup/GafferUSD/cyclesLights.py
@@ -0,0 +1,53 @@
+##########################################################################
+#
+#  Copyright (c) 2025, Alex Fuller. All rights reserved.
+#
+#  Redistribution and use in source and binary forms, with or without
+#  modification, are permitted provided that the following conditions are
+#  met:
+#
+#      * Redistributions of source code must retain the above
+#        copyright notice, this list of conditions and the following
+#        disclaimer.
+#
+#      * Redistributions in binary form must reproduce the above
+#        copyright notice, this list of conditions and the following
+#        disclaimer in the documentation and/or other materials provided with
+#        the distribution.
+#
+#      * Neither the name of John Haddon nor the names of
+#        any other contributors to this software may be used to endorse or
+#        promote products derived from this software without specific prior
+#        written permission.
+#
+#  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+#  IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+#  THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+#  PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+#  CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+#  EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+#  PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+#  PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+#  LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+#  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+#  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#
+##########################################################################
+
+import pathlib
+
+from pxr import Plug
+
+# Register a USD plugin that adds Cycles-specific auto-apply schemas for
+# UsdLux lights. We deliberately don't add this to the `PXR_PLUGINPATH_NAME`
+# search path because we don't want it to be loaded in any third-party
+# applications that Gaffer might launch as subprocessses. So instead we
+# register it manually with `RegisterPlugins`. See `GafferCycles.usda`
+# for more details.
+
+try :
+	import GafferCycles
+	Plug.Registry().RegisterPlugins( str( pathlib.Path( GafferCycles.__file__ ).parents[2] / "plugin" / "GafferCycles" / "plugInfo.json" ) )
+except ImportError :
+	# GafferCycles not available
+	pass
diff --git a/startup/gui/lightEditor.py b/startup/gui/lightEditor.py
index 584070579ec..f6c992a86f9 100644
--- a/startup/gui/lightEditor.py
+++ b/startup/gui/lightEditor.py
@@ -40,6 +40,44 @@
 import Gaffer
 import GafferSceneUI
 
+# UsdLux lights
+
+Gaffer.Metadata.registerValue( GafferSceneUI.LightEditor.Settings, "attribute", "preset:USD", "light" )
+
+GafferSceneUI.LightEditor.registerParameter( "light", "color" )
+GafferSceneUI.LightEditor.registerParameter( "light", "intensity" )
+GafferSceneUI.LightEditor.registerParameter( "light", "exposure" )
+GafferSceneUI.LightEditor.registerParameter( "light", "colorTemperature" )
+GafferSceneUI.LightEditor.registerParameter( "light", "enableColorTemperature" )
+GafferSceneUI.LightEditor.registerParameter( "light", "normalize" )
+GafferSceneUI.LightEditor.registerParameter( "light", "diffuse" )
+GafferSceneUI.LightEditor.registerParameter( "light", "specular" )
+
+GafferSceneUI.LightEditor.registerParameter( "light", "width", "Geometry" )
+GafferSceneUI.LightEditor.registerParameter( "light", "height", "Geometry" )
+GafferSceneUI.LightEditor.registerParameter( "light", "radius", "Geometry" )
+GafferSceneUI.LightEditor.registerParameter( "light", "treatAsPoint", "Geometry" )
+GafferSceneUI.LightEditor.registerParameter( "light", "length", "Geometry" )
+GafferSceneUI.LightEditor.registerParameter( "light", "treatAsLine", "Geometry" )
+GafferSceneUI.LightEditor.registerParameter( "light", "angle", "Geometry" )
+
+GafferSceneUI.LightEditor.registerParameter( "light", "texture:file", "Texture" )
+GafferSceneUI.LightEditor.registerParameter( "light", "texture:format", "Texture" )
+
+GafferSceneUI.LightEditor.registerParameter( "light", "shaping:cone:angle", "Shaping" )
+GafferSceneUI.LightEditor.registerParameter( "light", "shaping:cone:softness", "Shaping" )
+GafferSceneUI.LightEditor.registerParameter( "light", "shaping:focus", "Shaping" )
+GafferSceneUI.LightEditor.registerParameter( "light", "shaping:focusTint", "Shaping" )
+GafferSceneUI.LightEditor.registerParameter( "light", "shaping:ies:file", "Shaping" )
+GafferSceneUI.LightEditor.registerParameter( "light", "shaping:ies:angleScale", "Shaping" )
+GafferSceneUI.LightEditor.registerParameter( "light", "shaping:ies:normalize", "Shaping" )
+
+GafferSceneUI.LightEditor.registerParameter( "light", "shadow:enable", "Shadow" )
+GafferSceneUI.LightEditor.registerParameter( "light", "shadow:color", "Shadow" )
+GafferSceneUI.LightEditor.registerParameter( "light", "shadow:distance", "Shadow" )
+GafferSceneUI.LightEditor.registerParameter( "light", "shadow:falloff", "Shadow" )
+GafferSceneUI.LightEditor.registerParameter( "light", "shadow:falloffGamma", "Shadow" )
+
 if os.environ.get( "CYCLES_ROOT" ) and os.environ.get( "GAFFERCYCLES_HIDE_UI", "" ) != "1" :
 
 	Gaffer.Metadata.registerValue( GafferSceneUI.LightEditor.Settings, "attribute", "preset:Cycles", "cycles:light" )
@@ -65,6 +103,18 @@
 
 	Gaffer.Metadata.registerValue( GafferSceneUI.LightEditor.Settings, "attribute", "userDefault", "cycles:light" )
 
+	# Register Cycles-specific parameters for USD lights.
+	for parameter in [
+		"lightgroup",
+		"use_mis", "use_camera", "use_diffuse", "use_glossy", "use_transmission", "use_scatter", "use_caustics",
+		"spread", "map_resolution", "max_bounces"
+	] :
+		GafferSceneUI.LightEditor.registerParameter(
+			"light", f"cycles:{parameter}", "Cycles",
+			columnName = parameter.replace( "cycles:", "" )
+		)
+
+
 with IECore.IgnoredExceptions( ImportError ) :
 
 	# This import appears unused, but it is intentional; it prevents us from
@@ -92,44 +142,6 @@
 	Gaffer.Metadata.registerValue( GafferSceneUI.LightEditor.Settings, "attribute", "userDefault", "osl:light" )
 
 
-# UsdLux lights
-
-Gaffer.Metadata.registerValue( GafferSceneUI.LightEditor.Settings, "attribute", "preset:USD", "light" )
-
-GafferSceneUI.LightEditor.registerParameter( "light", "color" )
-GafferSceneUI.LightEditor.registerParameter( "light", "intensity" )
-GafferSceneUI.LightEditor.registerParameter( "light", "exposure" )
-GafferSceneUI.LightEditor.registerParameter( "light", "colorTemperature" )
-GafferSceneUI.LightEditor.registerParameter( "light", "enableColorTemperature" )
-GafferSceneUI.LightEditor.registerParameter( "light", "normalize" )
-GafferSceneUI.LightEditor.registerParameter( "light", "diffuse" )
-GafferSceneUI.LightEditor.registerParameter( "light", "specular" )
-
-GafferSceneUI.LightEditor.registerParameter( "light", "width", "Geometry" )
-GafferSceneUI.LightEditor.registerParameter( "light", "height", "Geometry" )
-GafferSceneUI.LightEditor.registerParameter( "light", "radius", "Geometry" )
-GafferSceneUI.LightEditor.registerParameter( "light", "treatAsPoint", "Geometry" )
-GafferSceneUI.LightEditor.registerParameter( "light", "length", "Geometry" )
-GafferSceneUI.LightEditor.registerParameter( "light", "treatAsLine", "Geometry" )
-GafferSceneUI.LightEditor.registerParameter( "light", "angle", "Geometry" )
-
-GafferSceneUI.LightEditor.registerParameter( "light", "texture:file", "Texture" )
-GafferSceneUI.LightEditor.registerParameter( "light", "texture:format", "Texture" )
-
-GafferSceneUI.LightEditor.registerParameter( "light", "shaping:cone:angle", "Shaping" )
-GafferSceneUI.LightEditor.registerParameter( "light", "shaping:cone:softness", "Shaping" )
-GafferSceneUI.LightEditor.registerParameter( "light", "shaping:focus", "Shaping" )
-GafferSceneUI.LightEditor.registerParameter( "light", "shaping:focusTint", "Shaping" )
-GafferSceneUI.LightEditor.registerParameter( "light", "shaping:ies:file", "Shaping" )
-GafferSceneUI.LightEditor.registerParameter( "light", "shaping:ies:angleScale", "Shaping" )
-GafferSceneUI.LightEditor.registerParameter( "light", "shaping:ies:normalize", "Shaping" )
-
-GafferSceneUI.LightEditor.registerParameter( "light", "shadow:enable", "Shadow" )
-GafferSceneUI.LightEditor.registerParameter( "light", "shadow:color", "Shadow" )
-GafferSceneUI.LightEditor.registerParameter( "light", "shadow:distance", "Shadow" )
-GafferSceneUI.LightEditor.registerParameter( "light", "shadow:falloff", "Shadow" )
-GafferSceneUI.LightEditor.registerParameter( "light", "shadow:falloffGamma", "Shadow" )
-
 # Arnold lights
 
 with IECore.IgnoredExceptions( ImportError ) :
diff --git a/startup/gui/usd.py b/startup/gui/usd.py
index 8b0de997aaf..3b864938328 100644
--- a/startup/gui/usd.py
+++ b/startup/gui/usd.py
@@ -35,6 +35,7 @@
 #
 ##########################################################################
 
+import os
 import Gaffer
 import GafferUSD
 
@@ -54,3 +55,15 @@
 	"samples", "volume_samples", "resolution"
 ] ) :
 	Gaffer.Metadata.registerValue( GafferUSD.USDLight, f"parameters.arnold:{parameter}", "layout:index", 1000 + i )
+
+# Change Cycles ordering.
+for i, parameter in enumerate( [
+	"lightgroup",
+	"use_mis", "use_camera", "use_diffuse", "use_glossy", "use_transmission", "use_scatter", "use_caustics",
+	"spread", "map_resolution", "max_bounces"
+] ) :
+	Gaffer.Metadata.registerValue( GafferUSD.USDLight, f"parameters.cycles:{parameter}", "layout:index", 2000 + i )
+
+# Only show the Cycles parameters if Cycles exists and not hidden
+Gaffer.Metadata.registerValue( GafferUSD.USDLight, "parameters", "layout:activator:cyclesUIEnabled", lambda x : os.environ.get( "CYCLES_ROOT" ) and os.environ.get( "GAFFERCYCLES_HIDE_UI", "" ) != "1" )
+Gaffer.Metadata.registerValue( GafferUSD.USDLight, "parameters.cycles:*", "layout:visibilityActivator", "cyclesUIEnabled" )
diff --git a/usdSchemas/GafferCycles.usda b/usdSchemas/GafferCycles.usda
new file mode 100644
index 00000000000..ae0d00ac3ed
--- /dev/null
+++ b/usdSchemas/GafferCycles.usda
@@ -0,0 +1,130 @@
+#usda 1.0
+(
+	subLayers = [
+		@usdLux/schema.usda@,
+		@usd/schema.usda@
+	]
+)
+
+over "GLOBAL" (
+	customData = {
+		string libraryName = "GafferCycles"
+		bool skipCodeGeneration = 1
+		bool useLiteralIdentifier = 1
+	}
+)
+{
+}
+
+# Here we define a bunch of codeless auto-apply API schemas for extending the
+# standard UsdLux lights with inputs specific to Cycles. This approach is
+# modelled on the one used by UsdRiPxr to add RenderMan-specific inputs, and
+# we believe is the one Pixar intends everyone to use.
+
+class "GafferCyclesLightAPI" (
+	customData = {
+		token[] apiSchemaAutoApplyTo = [ "DistantLight", "DiskLight", "DomeLight", "RectLight", "SphereLight" ]
+		string apiSchemaType = "singleApply"
+		string className = "GafferCyclesLightAPI"
+	}
+	inherits = </APISchemaBase>
+)
+{
+
+	string inputs:cycles:lightgroup = "" (
+		displayGroup = "Basic"
+		displayName = "Light Group (Cycles)"
+	)
+
+	bool inputs:cycles:use_mis = true (
+		displayGroup = "Refine"
+		displayName = "MIS (Cycles)"
+	)
+
+	bool inputs:cycles:use_camera = true (
+		displayGroup = "Refine"
+		displayName = "Camera (Cycles)"
+	)
+
+	bool inputs:cycles:use_diffuse = true (
+		displayGroup = "Refine"
+		displayName = "Diffuse (Cycles)"
+	)
+
+	bool inputs:cycles:use_glossy = true (
+		displayGroup = "Refine"
+		displayName = "Glossy (Cycles)"
+	)
+
+	bool inputs:cycles:use_transmission = true (
+		displayGroup = "Refine"
+		displayName = "Transmission (Cycles)"
+	)
+
+	bool inputs:cycles:use_scatter = true (
+		displayGroup = "Refine"
+		displayName = "Volume Scatter (Cycles)"
+	)
+
+	bool inputs:cycles:use_caustics = false (
+		displayGroup = "Refine"
+		displayName = "Shadow Caustics (Cycles)"
+	)
+
+	int inputs:cycles:max_bounces = 1024 (
+		displayGroup = "Refine"
+		displayName = "Max Bounces (Cycles)"
+	)
+
+}
+
+class "GafferCyclesDiskLightAPI" (
+	customData = {
+		token[] apiSchemaAutoApplyTo = ["DiskLight"]
+		string apiSchemaType = "singleApply"
+		string className = "GafferCyclesDiskLightAPI"
+	}
+	inherits = </APISchemaBase>
+)
+{
+
+	float inputs:cycles:spread = 180.0 (
+		displayGroup = "Geometry"
+		displayName = "Spread (Cycles)"
+	)
+
+}
+
+class "GafferCyclesQuadLightAPI" (
+	customData = {
+		token[] apiSchemaAutoApplyTo = ["RectLight"]
+		string apiSchemaType = "singleApply"
+		string className = "GafferCyclesQuadLightAPI"
+	}
+	inherits = </APISchemaBase>
+)
+{
+
+	float inputs:cycles:spread = 180.0 (
+		displayGroup = "Geometry"
+		displayName = "Spread (Cycles)"
+	)
+
+}
+
+class "GafferCyclesBackgroundLightAPI" (
+	customData = {
+		token[] apiSchemaAutoApplyTo = ["DomeLight"]
+		string apiSchemaType = "singleApply"
+		string className = "GafferCyclesBackgroundLightAPI"
+	}
+	inherits = </APISchemaBase>
+)
+{
+
+	int inputs:cycles:map_resolution = 1024 (
+		displayGroup = "Sampling"
+		displayName = "Map Resolution (Cycles)"
+	)
+
+}