diff --git a/hub/exports/building_energy/idf.py b/hub/exports/building_energy/idf.py
index 2d3289ae..8b1b09c9 100644
--- a/hub/exports/building_energy/idf.py
+++ b/hub/exports/building_energy/idf.py
@@ -11,6 +11,7 @@ from pathlib import Path
 from geomeppy import IDF
 import hub.helpers.constants as cte
 from hub.city_model_structure.attributes.schedule import Schedule
+from hub.city_model_structure.building_demand.thermal_zone import ThermalZone
 
 
 class Idf:
@@ -337,13 +338,15 @@ class Idf:
                            Activity_Level_Schedule_Name=f'Activity Level schedules {thermal_zone.usage_name}'
                            )
 
-  def _add_lighting(self, thermal_zone, zone_name):
+  def _add_lighting(self, thermal_zone: ThermalZone, zone_name: str):
     fraction_radiant = thermal_zone.lighting.radiative_fraction
+    # todo: fraction visible should come from catalog
     fraction_visible = 0.3
     method = 'Watts/Area'
     # todo: check the value of the factor to increase the density for the change of multizone to unizone
-    factor_size = 1 # thermal_zone.total_floor_area/self.internal_zone.area
+    factor_size = thermal_zone.total_floor_area / thermal_zone.footprint_area
     watts_per_zone_floor_area = thermal_zone.lighting.density*factor_size
+    # todo: fraction replaceable should come from catalog
     fraction_replaceable = 1
     subcategory = f'ELECTRIC EQUIPMENT#{zone_name}#GeneralLights'