diff --git a/datatypes/epc/domain/tests/test_from_rdsap_schema.py b/datatypes/epc/domain/tests/test_from_rdsap_schema.py
index 3ff99b4e..f5077eac 100644
--- a/datatypes/epc/domain/tests/test_from_rdsap_schema.py
+++ b/datatypes/epc/domain/tests/test_from_rdsap_schema.py
@@ -1605,3 +1605,35 @@ class TestRdSap18_0ReducedFieldSynthesis:
         # Assert — every synthesised window has an int glazing_type, not "ND".
         assert result.sap_windows
         assert all(isinstance(w.glazing_type, int) for w in result.sap_windows)
+
+    def test_lighting_counts_incandescent_remainder_and_low_energy_as_lel(
+        self,
+    ) -> None:
+        # Arrange — ADR-0028: 18.0 gives total + low-energy OUTLET counts, not an
+        # LED/CFL/incandescent split (matches 20.0.0). The non-low-energy
+        # remainder is incandescent (else lighting energy is understated); the
+        # low-energy outlets feed the calculator's LEL path. A cert with some
+        # incandescent (non-low-energy) outlets.
+        corpus = _load_18_0_corpus()
+        if not corpus:
+            pytest.skip("no RdSAP-Schema-18.0 corpus harvested")
+        cert = next(
+            (
+                c
+                for c in corpus
+                if (c.get("fixed_lighting_outlets_count") or 0)
+                > (c.get("low_energy_fixed_lighting_outlets_count") or 0)
+            ),
+            None,
+        )
+        if cert is None:
+            pytest.skip("no corpus cert with incandescent lighting")
+        total = cert["fixed_lighting_outlets_count"]
+        low = cert["low_energy_fixed_lighting_outlets_count"]
+
+        # Act
+        result = EpcPropertyDataMapper.from_api_response(cert)
+
+        # Assert
+        assert result.incandescent_fixed_lighting_bulbs_count == total - low
+        assert result.low_energy_fixed_lighting_bulbs_count == low