Always call update_use_power() instead of directly setting the use_power var.

- This will let us react to the change appropriately.
- While we're here, lets define some constants so we can stop using bare numbers.
- Always use those constants when calling update_use_power()

code/modules/power/antimatter/control.dm

@@ -211,10 +211,10 @@
 /obj/machinery/power/am_control_unit/proc/toggle_power()
 	active = !active
 	if(active)
-		use_power = 2
+		update_use_power(USE_POWER_ACTIVE)
 		visible_message("The [src.name] starts up.")
 	else
-		use_power = 1
+		update_use_power(USE_POWER_IDLE)
 		visible_message("The [src.name] shuts down.")
 	update_icon()
 	return

code/modules/power/fusion/core/_core.dm

@@ -70,7 +70,7 @@ var/list/fusion_cores = list()
 	owned_field = new(loc, src)
 	owned_field.ChangeFieldStrength(field_strength)
 	icon_state = "core1"
-	use_power = 2
+	update_use_power(USE_POWER_ACTIVE)
 	. = 1
 
 /obj/machinery/power/fusion_core/proc/Shutdown(var/force_rupture)
@@ -82,7 +82,7 @@ var/list/fusion_cores = list()
 			owned_field.RadiateAll()
 		qdel(owned_field)
 		owned_field = null
-	use_power = 1
+	update_use_power(USE_POWER_IDLE)
 
 /obj/machinery/power/fusion_core/proc/AddParticles(var/name, var/quantity = 1)
 	if(owned_field)

code/modules/power/fusion/fuel_assembly/fuel_injector.dm

@@ -103,13 +103,13 @@ var/list/fuel_injectors = list()
 	if(!injecting && cur_assembly)
 		icon_state = "injector1"
 		injecting = 1
-		use_power = 1
+		update_use_power(USE_POWER_IDLE)
 
 /obj/machinery/fusion_fuel_injector/proc/StopInjecting()
 	if(injecting)
 		injecting = 0
 		icon_state = "injector0"
-		use_power = 0
+		update_use_power(USE_POWER_OFF)
 
 /obj/machinery/fusion_fuel_injector/proc/Inject()
 	if(!injecting)

code/modules/power/generator.dm

@@ -156,7 +156,7 @@
 		user.visible_message("[user.name] [anchored ? "secures" : "unsecures"] the bolts holding [src.name] to the floor.", \
 					"You [anchored ? "secure" : "unsecure"] the bolts holding [src] to the floor.", \
 					"You hear a ratchet.")
-		use_power = anchored
+		update_use_power(anchored ? USE_POWER_IDLE : USE_POWER_ACTIVE)
 		if(anchored) // Powernet connection stuff.
 			connect_to_network()
 		else

code/modules/power/lighting.dm

@@ -320,10 +320,10 @@ var/global/list/light_type_cache = list()
 					on = 0
 					set_light(0)
 			else
-				use_power = 2
+				update_use_power(USE_POWER_ACTIVE)
 				set_light(brightness_range, brightness_power, brightness_color)
 	else
-		use_power = 1
+		update_use_power(USE_POWER_IDLE)
 		set_light(0)
 
 	active_power_usage = ((light_range * light_power) * LIGHTING_POWER_FACTOR)

code/modules/power/singularity/particle_accelerator/particle_accelerator.dm

@@ -383,10 +383,10 @@ So, hopefully this is helpful if any more icons are to be added/changed/wonderin
 		if(src.construction_state < 3)//Was taken apart, update state
 			update_state()
 			if(use_power)
-				use_power = 0
+				update_use_power(USE_POWER_OFF)
 		src.construction_state = temp_state
 		if(src.construction_state >= 3)
-			use_power = 1
+			update_use_power(USE_POWER_IDLE)
 		update_icon()
 		return 1
 	return 0

code/modules/power/singularity/particle_accelerator/particle_control.dm

@@ -42,7 +42,7 @@
 
 /obj/machinery/particle_accelerator/control_box/update_state()
 	if(construction_state < 3)
-		update_use_power(0)
+		update_use_power(USE_POWER_OFF)
 		assembled = 0
 		active = 0
 		for(var/obj/structure/particle_accelerator/part in connected_parts)
@@ -52,7 +52,7 @@
 		connected_parts = list()
 		return
 	if(!part_scan())
-		update_use_power(1)
+		update_use_power(USE_POWER_IDLE)
 		active = 0
 		connected_parts = list()
 
@@ -138,9 +138,9 @@
 	..()
 	if(stat & NOPOWER)
 		active = 0
-		update_use_power(0)
+		update_use_power(USE_POWER_OFF)
 	else if(!stat && construction_state == 3)
-		update_use_power(1)
+		update_use_power(USE_POWER_IDLE)
 
 
 /obj/machinery/particle_accelerator/control_box/process()
@@ -212,13 +212,13 @@
 	message_admins("PA Control Computer turned [active ?"ON":"OFF"] by [key_name(usr, usr.client)](<A HREF='?_src_=holder;adminmoreinfo=\ref[usr]'>?</A>) in ([x],[y],[z] - <A HREF='?_src_=holder;adminplayerobservecoodjump=1;X=[x];Y=[y];Z=[z]'>JMP</a>)",0,1)
 	log_game("PACCEL([x],[y],[z]) [key_name(usr)] turned [active?"ON":"OFF"].")
 	if(active)
-		update_use_power(2)
+		update_use_power(USE_POWER_ACTIVE)
 		for(var/obj/structure/particle_accelerator/part in connected_parts)
 			part.strength = src.strength
 			part.powered = 1
 			part.update_icon()
 	else
-		update_use_power(1)
+		update_use_power(USE_POWER_IDLE)
 		for(var/obj/structure/particle_accelerator/part in connected_parts)
 			part.strength = null
 			part.powered = 0

code/modules/power/supermatter/setup_supermatter.dm

@@ -126,7 +126,7 @@ GLOBAL_LIST_BOILERPLATE(all_engine_setup_markers, /obj/effect/engine_setup)
 		log_and_message_admins("## WARNING: Unable to locate pump at [x] [y] [z]!")
 		return SETUP_WARNING
 	P.target_pressure = P.max_pressure_setting
-	P.use_power = 1
+	P.update_use_power(USE_POWER_IDLE)
 	P.update_icon()
 	return SETUP_OK
 
@@ -259,7 +259,7 @@ GLOBAL_LIST_BOILERPLATE(all_engine_setup_markers, /obj/effect/engine_setup)
 				return SETUP_WARNING
 		F.rebuild_filtering_list()
 
-	F.use_power = 1
+	F.update_use_power(USE_POWER_IDLE)
 	F.update_icon()
 	return SETUP_OK