diff --git a/src/playsim/a_dynlight.cpp b/src/playsim/a_dynlight.cpp
index c8982528b..4025abfb7 100644
--- a/src/playsim/a_dynlight.cpp
+++ b/src/playsim/a_dynlight.cpp
@@ -113,6 +113,7 @@ void AttachLight(AActor *self)
 
 	light->pSpotInnerAngle = &self->AngleVar(NAME_SpotInnerAngle);
 	light->pSpotOuterAngle = &self->AngleVar(NAME_SpotOuterAngle);
+	light->lightDefIntensity = 1.0;
 	light->pPitch = &self->Angles.Pitch;
 	light->pLightFlags = (LightFlags*)&self->IntVar(NAME_lightflags);
 	light->pArgs = self->args;
@@ -863,7 +864,7 @@ DEFINE_ACTION_FUNCTION_NATIVE(AActor, A_AttachLightDef, AttachLightDef)
 //
 //==========================================================================
 
-int AttachLightDirect(AActor *self, int _lightid, int type, int color, int radius1, int radius2, int flags, double ofs_x, double ofs_y, double ofs_z, double param, double spoti, double spoto, double spotp)
+int AttachLightDirect(AActor *self, int _lightid, int type, int color, int radius1, int radius2, int flags, double ofs_x, double ofs_y, double ofs_z, double param, double spoti, double spoto, double spotp, double intensity)
 {
 	FName lightid = FName(ENamedName(_lightid));
 	auto userlight = self->UserLights[FindUserLight(self, lightid, true)];
@@ -879,6 +880,7 @@ int AttachLightDirect(AActor *self, int _lightid, int type, int color, int radiu
 	userlight->SetParameter(type == PulseLight? param*TICRATE : param*360.);
 	userlight->SetSpotInnerAngle(spoti);
 	userlight->SetSpotOuterAngle(spoto);
+	userlight->SetLightDefIntensity(intensity);
 	if (spotp >= -90. && spotp <= 90.)
 	{
 		userlight->SetSpotPitch(spotp);
@@ -908,7 +910,8 @@ DEFINE_ACTION_FUNCTION_NATIVE(AActor, A_AttachLight, AttachLightDirect)
 	PARAM_FLOAT(spoti);
 	PARAM_FLOAT(spoto);
 	PARAM_FLOAT(spotp);
-	ACTION_RETURN_BOOL(AttachLightDirect(self, lightid.GetIndex(), type, color, radius1, radius2, flags, ofs_x, ofs_y, ofs_z, parami, spoti, spoto, spotp));
+	PARAM_FLOAT(intensity);
+	ACTION_RETURN_BOOL(AttachLightDirect(self, lightid.GetIndex(), type, color, radius1, radius2, flags, ofs_x, ofs_y, ofs_z, parami, spoti, spoto, spotp, intensity));
 }
 
 //==========================================================================
diff --git a/src/playsim/a_dynlight.h b/src/playsim/a_dynlight.h
index 5424a4a53..2f8bea462 100644
--- a/src/playsim/a_dynlight.h
+++ b/src/playsim/a_dynlight.h
@@ -77,6 +77,7 @@ public:
 	void SetDontLightOthers(bool on) { if (on) m_lightFlags |= LF_DONTLIGHTOTHERS; else m_lightFlags &= ~LF_DONTLIGHTOTHERS; }
 	void SetDontLightMap(bool on) { if (on) m_lightFlags |= LF_DONTLIGHTMAP; else m_lightFlags &= ~LF_DONTLIGHTMAP; }
 	void SetNoShadowmap(bool on) { if (on) m_lightFlags |= LF_NOSHADOWMAP; else m_lightFlags &= ~LF_NOSHADOWMAP; }
+	void SetLightDefIntensity(double i) { m_LightDefIntensity = i; }
 	void SetSpot(bool spot) { if (spot) m_lightFlags |= LF_SPOT; else m_lightFlags &= ~LF_SPOT; }
 	void SetSpotInnerAngle(double angle) { m_spotInnerAngle = DAngle::fromDeg(angle); }
 	void SetSpotOuterAngle(double angle) { m_spotOuterAngle = DAngle::fromDeg(angle); }
@@ -128,6 +129,7 @@ protected:
 	DAngle m_spotInnerAngle = DAngle::fromDeg(10.0);
 	DAngle m_spotOuterAngle = DAngle::fromDeg(25.0);
 	DAngle m_pitch = nullAngle;
+	double m_LightDefIntensity = 1.0; // Light over/underbright multiplication for GLDEFS-defined lights
 	
 	friend FSerializer &Serialize(FSerializer &arc, const char *key, FLightDefaults &value, FLightDefaults *def);
 };
@@ -231,6 +233,7 @@ struct FDynamicLight
 	int GetBlue() const { return pArgs[LIGHT_BLUE]; }
 	int GetIntensity() const { return pArgs[LIGHT_INTENSITY]; }
 	int GetSecondaryIntensity() const { return pArgs[LIGHT_SECONDARY_INTENSITY]; }
+	double GetLightDefIntensity() const { return lightDefIntensity; }
 
 	bool IsSubtractive() const { return !!((*pLightFlags) & LF_SUBTRACTIVE); }
 	bool IsAdditive() const { return !!((*pLightFlags) & LF_ADDITIVE); }
@@ -293,6 +296,8 @@ public:
 	bool swapped;
 	bool explicitpitch;
 
+	double lightDefIntensity;
+
 	FDynamicLightTouchLists touchlists;
 };
 
diff --git a/src/r_data/a_dynlightdata.cpp b/src/r_data/a_dynlightdata.cpp
index c20c8d2e9..081eb1089 100644
--- a/src/r_data/a_dynlightdata.cpp
+++ b/src/r_data/a_dynlightdata.cpp
@@ -81,6 +81,7 @@ FSerializer &Serialize(FSerializer &arc, const char *key, FLightDefaults &value,
 			("spotinner", value.m_spotInnerAngle)
 			("spotouter", value.m_spotOuterAngle)
 			("pitch", value.m_pitch)
+			("lightdefintensity", value.m_LightDefIntensity)
 		.EndObject();
 	}
 	return arc;
@@ -125,6 +126,7 @@ void FLightDefaults::ApplyProperties(FDynamicLight * light) const
 	light->m_active = true;
 	light->lighttype = m_type;
 	light->specialf1 = m_Param;
+	light->lightDefIntensity = m_LightDefIntensity;
 	light->pArgs = m_Args;
 	light->pLightFlags = &m_lightFlags;
 	if (m_lightFlags & LF_SPOT)
diff --git a/src/r_data/gldefs.cpp b/src/r_data/gldefs.cpp
index 6bdb4f2d5..4b6812d69 100644
--- a/src/r_data/gldefs.cpp
+++ b/src/r_data/gldefs.cpp
@@ -200,6 +200,7 @@ static const char *LightTags[]=
    "noshadowmap",
    "dontlightothers",
    "dontlightmap",
+   "intensity",
    nullptr
 };
 
@@ -226,6 +227,7 @@ enum {
    LIGHTTAG_NOSHADOWMAP,
    LIGHTTAG_DONTLIGHTOTHERS,
    LIGHTTAG_DONTLIGHTMAP,
+   LIGHTTAG_INTENSITY,
 };
 
 //==========================================================================
@@ -541,6 +543,9 @@ class GLDefsParser
 						defaults->SetSpotOuterAngle(outerAngle);
 					}
 					break;
+				case LIGHTTAG_INTENSITY:
+					defaults->SetLightDefIntensity(ParseFloat(sc));
+					break;
 				default:
 					sc.ScriptError("Unknown tag: %s\n", sc.String);
 				}
@@ -643,6 +648,9 @@ class GLDefsParser
 						defaults->SetSpotOuterAngle(outerAngle);
 					}
 					break;
+				case LIGHTTAG_INTENSITY:
+					defaults->SetLightDefIntensity(ParseFloat(sc));
+					break;
 				default:
 					sc.ScriptError("Unknown tag: %s\n", sc.String);
 				}
@@ -748,6 +756,9 @@ class GLDefsParser
 						defaults->SetSpotOuterAngle(outerAngle);
 					}
 					break;
+				case LIGHTTAG_INTENSITY:
+					defaults->SetLightDefIntensity(ParseFloat(sc));
+					break;
 				default:
 					sc.ScriptError("Unknown tag: %s\n", sc.String);
 				}
@@ -852,6 +863,9 @@ class GLDefsParser
 						defaults->SetSpotOuterAngle(outerAngle);
 					}
 					break;
+				case LIGHTTAG_INTENSITY:
+					defaults->SetLightDefIntensity(ParseFloat(sc));
+					break;
 				default:
 					sc.ScriptError("Unknown tag: %s\n", sc.String);
 				}
@@ -953,6 +967,9 @@ class GLDefsParser
 						defaults->SetSpotOuterAngle(outerAngle);
 					}
 					break;
+				case LIGHTTAG_INTENSITY:
+					defaults->SetLightDefIntensity(ParseFloat(sc));
+					break;
 				default:
 					sc.ScriptError("Unknown tag: %s\n", sc.String);
 				}
diff --git a/src/rendering/hwrenderer/hw_dynlightdata.cpp b/src/rendering/hwrenderer/hw_dynlightdata.cpp
index bf516e637..1bb7ec33a 100644
--- a/src/rendering/hwrenderer/hw_dynlightdata.cpp
+++ b/src/rendering/hwrenderer/hw_dynlightdata.cpp
@@ -95,6 +95,9 @@ void AddLightToList(FDynLightData &dld, int group, FDynamicLight * light, bool f
 	if (light->target && (light->target->renderflags2 & RF2_LIGHTMULTALPHA))
 		cs *= (float)light->target->Alpha;
 
+	// Multiply intensity from GLDEFS
+	cs *= (float)light->GetLightDefIntensity();
+
 	float r = light->GetRed() / 255.0f * cs;
 	float g = light->GetGreen() / 255.0f * cs;
 	float b = light->GetBlue() / 255.0f * cs;
diff --git a/src/rendering/hwrenderer/scene/hw_spritelight.cpp b/src/rendering/hwrenderer/scene/hw_spritelight.cpp
index ad2c59d7f..d3b164ba0 100644
--- a/src/rendering/hwrenderer/scene/hw_spritelight.cpp
+++ b/src/rendering/hwrenderer/scene/hw_spritelight.cpp
@@ -194,6 +194,11 @@ void HWDrawInfo::GetDynSpriteLight(AActor *self, float x, float y, float z, FSec
 							lb *= alpha;
 						}
 
+						// Get GLDEFS intensity
+						lr *= light->GetLightDefIntensity();
+						lg *= light->GetLightDefIntensity();
+						lb *= light->GetLightDefIntensity();
+
 						if (light->IsSubtractive())
 						{
 							float bright = (float)FVector3(lr, lg, lb).Length();
diff --git a/wadsrc/static/zscript/actors/actor.zs b/wadsrc/static/zscript/actors/actor.zs
index 4ce112424..aae41c81b 100644
--- a/wadsrc/static/zscript/actors/actor.zs
+++ b/wadsrc/static/zscript/actors/actor.zs
@@ -1356,7 +1356,7 @@ class Actor : Thinker native
 	action native void A_OverlayTranslation(int layer, name trname);
 	
 	native bool A_AttachLightDef(Name lightid, Name lightdef);
-	native bool A_AttachLight(Name lightid, int type, Color lightcolor, int radius1, int radius2, int flags = 0, Vector3 ofs = (0,0,0), double param = 0, double spoti = 10, double spoto = 25, double spotp = 0);
+	native bool A_AttachLight(Name lightid, int type, Color lightcolor, int radius1, int radius2, int flags = 0, Vector3 ofs = (0,0,0), double param = 0, double spoti = 10, double spoto = 25, double spotp = 0, double intensity = 1.0);
 	native bool A_RemoveLight(Name lightid);
 
 	//================================================