diff --git a/domain/sap10_calculator/rdsap/cert_to_inputs.py b/domain/sap10_calculator/rdsap/cert_to_inputs.py
index c7218cd8..ae4862a2 100644
--- a/domain/sap10_calculator/rdsap/cert_to_inputs.py
+++ b/domain/sap10_calculator/rdsap/cert_to_inputs.py
@@ -1572,6 +1572,91 @@ def _main_heating_primary_factor(
     return high_frac * high_factor + (1.0 - high_frac) * low_factor
 
 
+def _other_use_co2_factor_kg_per_kwh(
+    other_use: OtherUse,
+    tariff: Tariff,
+    monthly_kwh: tuple[float, ...],
+) -> Optional[float]:
+    """SAP 10.2 Table 12a Grid 2 (PDF p.191) + Table 12d (PDF p.194)
+    dual-rate monthly CO2 factor for "other electricity uses" (lighting,
+    pumps + fans, electric shower, etc.).
+
+    Per Table 12d header (p.194): "Where electricity is the fuel used,
+    the relevant set of factors in the table below should be used to
+    calculate the monthly CO2 emissions INSTEAD of the annual average
+    factor given in Table 12." For STANDARD tariff this means single
+    Table 12d code 30 monthly factors weighted by the end-use's profile.
+    For Grid-2-eligible off-peak tariffs (SEVEN_HOUR / TEN_HOUR) the
+    Grid 2 ALL_OTHER_USES / FANS_FOR_MECH_VENT high-rate fraction
+    blends Table 12d high-rate × low-rate codes per:
+
+        F_blended = high_frac × F_high + (1 − high_frac) × F_low
+
+    Grid 2 doesn't list EIGHTEEN_HOUR / TWENTY_FOUR_HOUR rows; those
+    tariffs fall through to single-code-30 monthly.
+
+    Mirrors `_main_heating_co2_factor_kg_per_kwh` for the Grid 2
+    end-uses. Returns None when the cascade can't form a factor (zero
+    monthly kWh in every month); callers fall back to the annual
+    `_STANDARD_ELECTRICITY_FUEL_CODE` Table 12 value."""
+    if tariff is Tariff.STANDARD:
+        return _effective_monthly_co2_factor(
+            monthly_kwh, _STANDARD_ELECTRICITY_FUEL_CODE,
+        )
+    try:
+        high_frac = other_use_high_rate_fraction(other_use, tariff)
+    except NotImplementedError:
+        return _effective_monthly_co2_factor(
+            monthly_kwh, _STANDARD_ELECTRICITY_FUEL_CODE,
+        )
+    codes = _TARIFF_HIGH_LOW_FUEL_CODES_TABLE_12.get(tariff)
+    if codes is None:
+        return _effective_monthly_co2_factor(
+            monthly_kwh, _STANDARD_ELECTRICITY_FUEL_CODE,
+        )
+    high_code, low_code = codes
+    high_factor = _effective_monthly_co2_factor(monthly_kwh, high_code)
+    low_factor = _effective_monthly_co2_factor(monthly_kwh, low_code)
+    if high_factor is None or low_factor is None:
+        return None
+    return high_frac * high_factor + (1.0 - high_frac) * low_factor
+
+
+def _other_use_primary_factor(
+    other_use: OtherUse,
+    tariff: Tariff,
+    monthly_kwh: tuple[float, ...],
+) -> Optional[float]:
+    """SAP 10.2 Table 12a Grid 2 (PDF p.191) + Table 12e (PDF p.195)
+    dual-rate monthly PE factor for "other electricity uses" — PE-side
+    mirror of `_other_use_co2_factor_kg_per_kwh`. Same dispatch shape:
+    STANDARD tariff → code 30 monthly cascade; SEVEN_HOUR / TEN_HOUR →
+    Grid 2 ALL_OTHER_USES / FANS_FOR_MECH_VENT blend; EIGHTEEN_HOUR /
+    TWENTY_FOUR_HOUR fall through to single-code-30. Returns None for
+    the zero-monthly-kWh degenerate case."""
+    if tariff is Tariff.STANDARD:
+        return _effective_monthly_pe_factor(
+            monthly_kwh, _STANDARD_ELECTRICITY_FUEL_CODE,
+        )
+    try:
+        high_frac = other_use_high_rate_fraction(other_use, tariff)
+    except NotImplementedError:
+        return _effective_monthly_pe_factor(
+            monthly_kwh, _STANDARD_ELECTRICITY_FUEL_CODE,
+        )
+    codes = _TARIFF_HIGH_LOW_FUEL_CODES_TABLE_12.get(tariff)
+    if codes is None:
+        return _effective_monthly_pe_factor(
+            monthly_kwh, _STANDARD_ELECTRICITY_FUEL_CODE,
+        )
+    high_code, low_code = codes
+    high_factor = _effective_monthly_pe_factor(monthly_kwh, high_code)
+    low_factor = _effective_monthly_pe_factor(monthly_kwh, low_code)
+    if high_factor is None or low_factor is None:
+        return None
+    return high_frac * high_factor + (1.0 - high_frac) * low_factor
+
+
 def _hot_water_co2_factor_kg_per_kwh(
     epc: EpcPropertyData,
     hw_monthly_kwh: tuple[float, ...],
@@ -4067,19 +4152,25 @@ def cert_to_inputs(
             epc,
             wh_result.output_monthly_kwh if wh_result is not None else (0.0,) * 12,
         ),
-        pumps_fans_co2_factor_kg_per_kwh=_effective_monthly_co2_factor(
+        # SAP 10.2 Table 12a Grid 2 (p.191) + Table 12d (p.194): pumps,
+        # lighting, and the electric-shower end-use all bill via the
+        # "All other uses" row → on off-peak tariffs blend the high /
+        # low Table 12d codes per the Grid 2 fraction. STANDARD tariff
+        # passes through to single-code-30 monthly. Mirrors the main-
+        # heating Grid 1 split landed in S0380.65.
+        pumps_fans_co2_factor_kg_per_kwh=_other_use_co2_factor_kg_per_kwh(
+            OtherUse.ALL_OTHER_USES, _rdsap_tariff(epc),
             _days_in_month_proportioned(pumps_fans_kwh, _DAYS_IN_MONTH),
-            _STANDARD_ELECTRICITY_FUEL_CODE,
         ),
-        lighting_co2_factor_kg_per_kwh=_effective_monthly_co2_factor(
-            lighting_monthly_kwh, _STANDARD_ELECTRICITY_FUEL_CODE,
+        lighting_co2_factor_kg_per_kwh=_other_use_co2_factor_kg_per_kwh(
+            OtherUse.ALL_OTHER_USES, _rdsap_tariff(epc), lighting_monthly_kwh,
         ),
         electric_shower_kwh_per_yr=(
             wh_result.electric_shower_kwh_per_yr if wh_result is not None else 0.0
         ),
-        electric_shower_co2_factor_kg_per_kwh=_effective_monthly_co2_factor(
+        electric_shower_co2_factor_kg_per_kwh=_other_use_co2_factor_kg_per_kwh(
+            OtherUse.ALL_OTHER_USES, _rdsap_tariff(epc),
             wh_result.electric_shower_monthly_kwh if wh_result is not None else (0.0,) * 12,
-            _STANDARD_ELECTRICITY_FUEL_CODE,
         ),
         pv_generation_kwh_per_yr=_pv_generation_kwh_per_yr(epc, climate),
         pv_export_credit_gbp_per_kwh=_pv_export_credit_gbp_per_kwh(),
@@ -4140,16 +4231,18 @@ def cert_to_inputs(
         secondary_heating_primary_factor=_secondary_heating_primary_factor(
             epc, energy_requirements_result.secondary_fuel_monthly_kwh,
         ),
-        pumps_fans_primary_factor=_effective_monthly_pe_factor(
+        # PE-side mirror of the Grid 2 dual-rate CO2 blend above —
+        # Table 12a Grid 2 (p.191) + Table 12e (p.195).
+        pumps_fans_primary_factor=_other_use_primary_factor(
+            OtherUse.ALL_OTHER_USES, _rdsap_tariff(epc),
             _days_in_month_proportioned(pumps_fans_kwh, _DAYS_IN_MONTH),
-            _STANDARD_ELECTRICITY_FUEL_CODE,
         ),
-        lighting_primary_factor=_effective_monthly_pe_factor(
-            lighting_monthly_kwh, _STANDARD_ELECTRICITY_FUEL_CODE,
+        lighting_primary_factor=_other_use_primary_factor(
+            OtherUse.ALL_OTHER_USES, _rdsap_tariff(epc), lighting_monthly_kwh,
         ),
-        electric_shower_primary_factor=_effective_monthly_pe_factor(
+        electric_shower_primary_factor=_other_use_primary_factor(
+            OtherUse.ALL_OTHER_USES, _rdsap_tariff(epc),
             wh_result.electric_shower_monthly_kwh if wh_result is not None else (0.0,) * 12,
-            _STANDARD_ELECTRICITY_FUEL_CODE,
         ),
         fuel_cost=_fuel_cost(
             epc=epc,
diff --git a/domain/sap10_calculator/rdsap/tests/test_cert_to_inputs.py b/domain/sap10_calculator/rdsap/tests/test_cert_to_inputs.py
index 97c0cc83..d7dd235c 100644
--- a/domain/sap10_calculator/rdsap/tests/test_cert_to_inputs.py
+++ b/domain/sap10_calculator/rdsap/tests/test_cert_to_inputs.py
@@ -2090,6 +2090,58 @@ def test_air_source_heat_pump_main_heating_zeroes_table_3a_combi_loss_per_sap_4_
         )
 
 
+def test_lighting_co2_factor_blends_table_12a_grid_2_with_table_12d_dual_rate_on_off_peak_certs() -> None:
+    """SAP 10.2 Table 12a Grid 2 (PDF p.191) + Table 12d (PDF p.194) —
+    "other electricity uses" (lighting, pumps + fans, electric shower) on
+    an off-peak tariff blend the dual-rate Table 12d high/low monthly CO2
+    factors per the Grid 2 ALL_OTHER_USES high-rate fraction. From the
+    spec text on p.194:
+
+        "Where electricity is the fuel used, the relevant set of factors
+         in the table below should be used to calculate the monthly CO2
+         emissions INSTEAD of the annual average factor given in
+         Table 12."
+
+    And Table 12a Grid 2 (PDF p.191) "Other electricity uses" row
+    "All other uses" × 10-hour tariff = 0.80 high-rate fraction.
+
+    Cert 000565 is on a Dual meter routed via §12 Rule 3 (heat pump
+    main → TEN_HOUR). The lighting CO2 factor must blend Table 12d
+    code 34 (10h high) and code 33 (10h low) monthly factors weighted
+    by the L11 lighting profile, NOT use code 30 alone (Slice S0380.65
+    landed this for main_heating; lighting / pumps_fans / electric_
+    shower were still on the code-30-only path).
+
+    Pre-S0380.82 cert 000565 cascade: lighting factor 0.1443 (code 30
+    monthly × L11 profile). Post: 0.1469 (Grid 2 blend) — pushes the
+    cohort CO2 residual from −8.92 kg/yr toward zero on the lighting
+    + pumps_fans + electric_shower trio.
+    """
+    # Arrange — mapper-driven cohort fixture (Dual meter / TEN_HOUR
+    # tariff, heat-pump main).
+    from domain.sap10_calculator.worksheet.tests import (
+        _elmhurst_worksheet_000565 as _w000565,
+    )
+    epc = _w000565.build_epc()
+
+    # Act
+    inputs = cert_to_inputs(epc)
+
+    # Assert — lighting CO2 factor lifted above the code-30-only baseline
+    # by the Grid 2 dual-rate blend. Pre-S0380.82 value 0.1443; post-fix
+    # ≥ 0.146 per the 0.80-weighted code 34 + 0.20-weighted code 33
+    # cascade.
+    pre_fix_baseline = 0.1444  # code 30 monthly × L11 profile
+    factor = inputs.lighting_co2_factor_kg_per_kwh
+    assert factor is not None and factor > pre_fix_baseline + 0.001, (
+        f"lighting_co2_factor_kg_per_kwh = {factor!r}; expected dual-rate "
+        f"Grid 2 blend > {pre_fix_baseline + 0.001:.4f} per SAP 10.2 "
+        f"Table 12a Grid 2 (p.191) + Table 12d (p.194). The cascade was "
+        f"applying code 30 alone — must now blend code 34 (10h high) and "
+        f"code 33 (10h low) at the 0.80 / 0.20 split."
+    )
+
+
 def test_rdsap_10_table_32_prices_charge_mains_gas_hot_water_at_3p48_per_kwh() -> None:
     """RdSAP 10 Specification §19.1 (PDF page 80-81) — the §10a fuel-cost
     block uses RdSAP 10 Table 32 (PDF page 95) prices, NOT SAP 10.2