diff --git a/tests/domain/modelling/fixtures/low_energy_lighting_some_leds_001431_after.pdf b/tests/domain/modelling/fixtures/low_energy_lighting_some_leds_001431_after.pdf
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diff --git a/tests/domain/modelling/fixtures/low_energy_lighting_some_leds_001431_before.pdf b/tests/domain/modelling/fixtures/low_energy_lighting_some_leds_001431_before.pdf
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diff --git a/tests/domain/modelling/fixtures/low_energy_lighting_zero_leds_001431_after.pdf b/tests/domain/modelling/fixtures/low_energy_lighting_zero_leds_001431_after.pdf
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diff --git a/tests/domain/modelling/fixtures/low_energy_lighting_zero_leds_001431_before.pdf b/tests/domain/modelling/fixtures/low_energy_lighting_zero_leds_001431_before.pdf
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diff --git a/tests/domain/modelling/test_elmhurst_cascade_pins.py b/tests/domain/modelling/test_elmhurst_cascade_pins.py
index fdf78eda..6bba36ef 100644
--- a/tests/domain/modelling/test_elmhurst_cascade_pins.py
+++ b/tests/domain/modelling/test_elmhurst_cascade_pins.py
@@ -37,6 +37,7 @@ from domain.modelling.generators.solid_wall_recommendation import (
     recommend_solid_wall,
 )
 from domain.modelling.generators.glazing_recommendation import recommend_glazing
+from domain.modelling.generators.lighting_recommendation import recommend_lighting
 from domain.modelling.scoring.overlay_applicator import apply_simulations
 from domain.modelling.recommendation import MeasureOption
 from domain.sap10_calculator.calculator import Sap10Calculator, SapResult
@@ -537,3 +538,41 @@ def test_secondary_glazing_overlay_reproduces_the_relodged_after() -> None:
     _assert_overlay_reproduces_after(
         before, after, recommendation.options[0].overlay
     )
+
+
+def test_lighting_overlay_reproduces_the_relodged_after_zero_existing_leds() -> None:
+    # Arrange — a dwelling with no LEDs (20 incandescent); the after re-lodges
+    # all 20 as LED. Lighting only changes bulb counts → Appendix L (232), with
+    # no fabric coupling, so the full-SAP pin closes cleanly.
+    before: EpcPropertyData = parse_recommendation_summary(
+        "low_energy_lighting_zero_leds_001431_before.pdf"
+    )
+    after: EpcPropertyData = parse_recommendation_summary(
+        "low_energy_lighting_zero_leds_001431_after.pdf"
+    )
+    recommendation: Recommendation | None = recommend_lighting(before, _AnyProduct())
+    assert recommendation is not None
+
+    # Act / Assert
+    _assert_overlay_reproduces_after(
+        before, after, recommendation.options[0].overlay
+    )
+
+
+def test_lighting_overlay_reproduces_the_relodged_after_some_existing_leds() -> None:
+    # Arrange — a dwelling with some LEDs already (5 LED + 15 incandescent); the
+    # after re-lodges all 20 as LED. Exercises the partial-upgrade path: the
+    # overlay tops led up to the total rather than starting from zero.
+    before: EpcPropertyData = parse_recommendation_summary(
+        "low_energy_lighting_some_leds_001431_before.pdf"
+    )
+    after: EpcPropertyData = parse_recommendation_summary(
+        "low_energy_lighting_some_leds_001431_after.pdf"
+    )
+    recommendation: Recommendation | None = recommend_lighting(before, _AnyProduct())
+    assert recommendation is not None
+
+    # Act / Assert
+    _assert_overlay_reproduces_after(
+        before, after, recommendation.options[0].overlay
+    )