Ok, done.

code/modules/power/lighting.dm

@@ -291,8 +291,7 @@
 	QDEL_NULL(cell)
 	return ..()
 
-/obj/machinery/light/update_icon()
-	cut_overlays()
+/obj/machinery/light/update_icon_state()
 	switch(status)		// set icon_states
 		if(LIGHT_OK)
 			var/area/A = get_base_area(src)
@@ -303,17 +302,20 @@
 					icon_state = "[base_state]_hijacked"
 				else
 					icon_state = "[base_state]"
-				if(on)
-					var/mutable_appearance/glowybit = mutable_appearance(overlayicon, base_state, ABOVE_LIGHTING_LAYER, ABOVE_LIGHTING_PLANE)
-					glowybit.alpha = CLAMP(light_power*250, 30, 200)
-					add_overlay(glowybit)
 		if(LIGHT_EMPTY)
 			icon_state = "[base_state]-empty"
 		if(LIGHT_BURNED)
 			icon_state = "[base_state]-burned"
 		if(LIGHT_BROKEN)
 			icon_state = "[base_state]-broken"
-	return
+
+/obj/machinery/light/update_overlays()
+	. = ..()
+	if(on && status == LIGHT_OK)
+		var/mutable_appearance/glowybit = mutable_appearance(overlayicon, base_state, ABOVE_LIGHTING_LAYER, ABOVE_LIGHTING_PLANE)
+		glowybit.alpha = CLAMP(light_power*250, 30, 200)
+		. += glowybit
+
 
 // update the icon_state and luminosity of the light depending on its state
 /obj/machinery/light/proc/update(trigger = TRUE)