Non-Domestic Lighting Requirements Under the FBS

The Future Buildings Standard sets a minimum general lighting efficacy of 105 luminaire lumens per circuit watt (lm/W) for new non-domestic buildings – effectively mandating LED lighting throughout. Combined with mandatory controls for occupancy sensing, daylight dimming, and time scheduling, the FBS significantly tightens lighting energy performance compared to Part L 2021. The notional building specification uses this efficacy as its baseline assumption (AD L2 2026, Section 5).

The 105 lm/W efficacy requirement

Internal general lighting in new non-domestic buildings must achieve an average luminaire efficacy of greater than 105 luminaire lumens per circuit watt. This is measured at the luminaire level (not the lamp level), meaning it accounts for optical losses in the fitting as well as any driver or control gear losses (AD L2 2026, para 5.65).

The government originally consulted on a notional lighting efficacy of 150 lm/W (consultation response, para 12.55, p114), but adopted 105 lm/W following industry feedback that the higher target was not cost-effective. This is still a 10.5% increase from the Part L 2021 notional of 95 lm/W (NCM 2021, para 71).

In practical terms, this requirement rules out fluorescent lighting in new installations and mandates high-quality LED luminaires throughout. While many modern LED products comfortably exceed 105 lm/W, designers must verify that the specified luminaires meet this threshold at the luminaire level - not just at the LED chip or lamp level, where quoted efficacies are typically higher.

The LENI alternative compliance route

As an alternative to the 105 lm/W efficacy requirement, compliance can be demonstrated through the Lighting Energy Numeric Indicator (LENI) method set out in Appendix B of AD L2 2026. The LENI represents the annual lighting energy consumption per square metre and must not exceed the values in Table B1 for the given illuminance level and operating hours (AD L2 2026, Appendix B).

For example, a space operating 3,000 hours per year at 300 lux must not exceed a LENI of 8.64 kWh/m² per year, while the same hours at 500 lux must not exceed 14.41 kWh/m² per year. The LENI route is most useful for specialist lighting designs where individual luminaires may not meet 105 lm/W but the overall installation achieves equivalent or better energy performance through controls and design optimisation.

Display lighting

Display lighting has separate, slightly lower efficacy requirements than general lighting (AD L2 2026, para 5.65):

• Average light source efficacy of greater than 95 light source lumens per circuit watt, or
• Rated power use no greater than 0.3 W/m² in each space, or
• A LENI no greater than the applicable Table B1 values

Display lighting must be installed on dedicated circuits and switched separately from general illuminance. This ensures that display lighting can be controlled independently – turned off outside trading hours, for example – without affecting general lighting provision (AD L2 2026, para 5.70).

High excitation purity light sources

Specialist light sources with high excitation purity (used in applications such as architectural accent lighting or stage lighting) have a lower efficacy threshold of 65 light source lumens per circuit watt. These are defined in Appendix A of AD L2 2026 (Table A1).

Lighting controls

The FBS requires comprehensive lighting controls to minimise energy waste. The controls strategy should follow BRE Digest 498 and address four key areas (AD L2 2026, paras 5.68–5.72):

Occupancy sensing

Automatic presence detection must be installed to turn off lighting when spaces are not in use. This applies to:

• All unoccupied spaces – corridors, stairwells, toilets, storage areas, plant rooms
• Occupied spaces where occupancy sensing is suitable – meeting rooms, individual offices, break rooms
• Hotel bedrooms – must use key-card switches and/or occupancy detection to ensure lighting is off when unoccupied

Daylight dimming and photo-switching

General lighting in occupied spaces with natural light must incorporate daylight controls – either photo-switching (on/off based on daylight level) or dimming (continuous adjustment to maintain target illuminance while reducing electrical lighting as daylight increases). Daylight dimming is more effective and is the expected approach for most perimeter zones in offices, schools, and similar buildings (AD L2 2026, para 5.69).

Time scheduling

Lighting should be controlled on a time schedule aligned with the building's operational hours. This prevents lighting from being left on during unoccupied periods – particularly important in buildings with regular operating patterns such as offices and schools. Time scheduling should work in conjunction with, not as a replacement for, occupancy sensing.

Metering

Internal general and display lighting must be metered. For buildings with total useful floor area greater than 1,000 m², automatic meter reading and data collection should be installed. This supports ongoing monitoring and enables building operators to identify lighting energy waste. Metering data is documented in the BRUKL report (AD L2 2026, para 4.19).

External lighting

External lighting in new buildings must be designed to CIBSE's SLL Code for Lighting and include automatic controls to switch off during daylight hours and periods when the building is not in operational use. Light spill and wasted light to the sky must be minimised (AD L2 2026, paras 5.73–5.75).

Exceptions apply to safety and security lighting, and luminaires with a maximum power consumption of less than 4 W.

Emergency lighting

Emergency lighting is subject to separate regulations and is not included in the Part L energy calculation. However, specifying LED emergency luminaires is consistent with the overall approach and avoids the maintenance burden of legacy lamp technologies. Where emergency luminaires form part of the general lighting installation (maintained emergency lighting), their efficacy contributes to the 105 lm/W average.

Lift car lighting

Lighting within lift cars – including display lighting in lift cars – must achieve an average luminaire efficacy of 105 luminaire lumens per circuit watt or greater, the same standard as general lighting elsewhere in the building (AD L2 2026, para 5.65).

FBS 2026 vs Part L 2021 – lighting comparison

The table below summarises the key differences between the FBS and Part L 2021 lighting requirements.

Lighting in existing buildings – consequential improvements

Existing buildings with a total useful floor area over 1,000 m² may trigger consequential improvements when extended or when fixed building services are installed or increased. Table D1 of AD L2 2026 requires upgrading general lighting with less than 60 light source lumens per circuit watt (serving areas greater than 100 m²) as a normally required improvement. The SBEM calculation models the impact of lighting upgrades on overall building performance (AD L2 2026, Appendix D).