diff --git a/packages/domain/src/domain/ml/demand.py b/packages/domain/src/domain/ml/demand.py
index 7a4810ba..c8b2c1f3 100644
--- a/packages/domain/src/domain/ml/demand.py
+++ b/packages/domain/src/domain/ml/demand.py
@@ -120,19 +120,23 @@ def predicted_hot_water_kwh(
 
 def predicted_lighting_kwh(
     total_floor_area_m2: Optional[float],
-    cfl_count: int,
-    led_count: int,
-    incandescent_count: int,
+    cfl_count: Optional[int],
+    led_count: Optional[int],
+    incandescent_count: Optional[int],
 ) -> float:
     """Annual lighting kWh (SAP10.2 Section L simplified).
 
     Base demand ~ 9.3 * TFA kWh/yr; reduced by low-energy bulb share.  LED
     bulbs cut consumption by ~50%, CFL by ~40%, incandescent by 0%.
+    Missing counts treated as zero.
     """
     if total_floor_area_m2 is None or total_floor_area_m2 <= 0:
         return 0.0
-    total_bulbs = max(1, cfl_count + led_count + incandescent_count)
-    led_share = led_count / total_bulbs
-    cfl_share = cfl_count / total_bulbs
+    cfl = cfl_count or 0
+    led = led_count or 0
+    inc = incandescent_count or 0
+    total_bulbs = max(1, cfl + led + inc)
+    led_share = led / total_bulbs
+    cfl_share = cfl / total_bulbs
     reduction = 0.5 * led_share + 0.4 * cfl_share
     return 9.3 * total_floor_area_m2 * (1.0 - reduction)