diff --git a/src/playsim/a_dynlight.cpp b/src/playsim/a_dynlight.cpp
index 71dc8db7d..7be30a73b 100644
--- a/src/playsim/a_dynlight.cpp
+++ b/src/playsim/a_dynlight.cpp
@@ -139,6 +139,7 @@ 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->shadowMinQuality = std::clamp(self->IntVar(NAME_shadowMinQuality), 0, 4);
@@ -1030,7 +1031,7 @@ 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)];
@@ -1046,6 +1047,7 @@ 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);
@@ -1075,7 +1077,8 @@ 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 f580ab87d..03aeea8b4 100644
--- a/src/playsim/a_dynlight.h
+++ b/src/playsim/a_dynlight.h
@@ -84,6 +84,7 @@ public:
 	{
 		shadowMinQuality = quality;
 	}
+	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); }
@@ -138,6 +139,7 @@ protected:
 	double SoftShadowRadius = 5.0;
 	double Linearity = 0.0;
 	int shadowMinQuality = 1; // default medium, 0 = low, 1 = medium, 2 = high, 3 = ultra
+	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);
 };
@@ -238,6 +240,7 @@ 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); }
@@ -312,6 +315,8 @@ public:
 
 	float lightStrength;
 
+	double lightDefIntensity;
+
 	TArray<AActor*> ActorList;
 	TArray<bool> ActorResult;
 
diff --git a/src/r_data/a_dynlightdata.cpp b/src/r_data/a_dynlightdata.cpp
index 471a5e67b..24d299314 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;
@@ -127,6 +128,7 @@ 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->pSoftShadowRadius = &SoftShadowRadius;
 
diff --git a/src/r_data/gldefs.cpp b/src/r_data/gldefs.cpp
index 7eb88724b..b5d8a1091 100644
--- a/src/r_data/gldefs.cpp
+++ b/src/r_data/gldefs.cpp
@@ -552,6 +552,7 @@ static const char *LightTags[]=
    "dontlightmap",
    "trace",
    "shadowminquality",
+   "intensity",
    nullptr
 };
 
@@ -580,6 +581,7 @@ enum {
    LIGHTTAG_DONTLIGHTMAP,
    LIGHTTAG_TRACE,
    LIGHTTAG_SHADOW_MINQUALITY,
+   LIGHTTAG_INTENSITY,
 };
 
 //==========================================================================
@@ -903,6 +905,9 @@ class GLDefsParser
 						defaults->SetSpotOuterAngle(outerAngle);
 					}
 					break;
+				case LIGHTTAG_INTENSITY:
+					defaults->SetLightDefIntensity(ParseFloat(sc));
+					break;
 				default:
 					sc.ScriptError("Unknown tag: %s\n", sc.String);
 				}
@@ -1011,6 +1016,9 @@ class GLDefsParser
 						defaults->SetSpotOuterAngle(outerAngle);
 					}
 					break;
+				case LIGHTTAG_INTENSITY:
+					defaults->SetLightDefIntensity(ParseFloat(sc));
+					break;
 				default:
 					sc.ScriptError("Unknown tag: %s\n", sc.String);
 				}
@@ -1122,6 +1130,9 @@ class GLDefsParser
 						defaults->SetSpotOuterAngle(outerAngle);
 					}
 					break;
+				case LIGHTTAG_INTENSITY:
+					defaults->SetLightDefIntensity(ParseFloat(sc));
+					break;
 				default:
 					sc.ScriptError("Unknown tag: %s\n", sc.String);
 				}
@@ -1232,6 +1243,9 @@ class GLDefsParser
 						defaults->SetSpotOuterAngle(outerAngle);
 					}
 					break;
+				case LIGHTTAG_INTENSITY:
+					defaults->SetLightDefIntensity(ParseFloat(sc));
+					break;
 				default:
 					sc.ScriptError("Unknown tag: %s\n", sc.String);
 				}
@@ -1339,6 +1353,9 @@ 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 b4eb326ed..d1bdd0e1b 100644
--- a/src/rendering/hwrenderer/hw_dynlightdata.cpp
+++ b/src/rendering/hwrenderer/hw_dynlightdata.cpp
@@ -101,6 +101,9 @@ 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();
+
 	info.r = light->GetRed() / 255.0f * cs;
 	info.g = light->GetGreen() / 255.0f * cs;
 	info.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 523a14f63..48394d7db 100644
--- a/src/rendering/hwrenderer/scene/hw_spritelight.cpp
+++ b/src/rendering/hwrenderer/scene/hw_spritelight.cpp
@@ -225,6 +225,11 @@ void HWDrawInfo::GetDynSpriteLight(AActor *self, sun_trace_cache_t * traceCache,
 							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 48588bcb6..50f8a8118 100644
--- a/wadsrc/static/zscript/actors/actor.zs
+++ b/wadsrc/static/zscript/actors/actor.zs
@@ -1322,7 +1322,7 @@ 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);
 
 	//================================================