Client: Siemens Gamesa
Architect: Race Cottam Associates

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At odds with established recommendations, there remains a trend to over-light the spaces in which we work. The CIBSE/SLL Lighting Guide LG7 and BCO Guide 2019 state that illumination at 300 lux is acceptable for screen-based tasks because modern devices provide their own back-lit light source. The higher levels of 400-500 lux commonly seen are only necessary where specific paper-based or fine detail tasks are undertaken.

Desk areas in densely occupied workplaces often account for just 10% to 14% of the floor area, so the energy we waste over-lighting circulation space can be considerable. The reticence to cut lighting levels is due primarily to the perception that suggesting a tenant install lighting to suit specific tasks would be perceived negatively and have a detrimental effect on the marketability of an asset. However, the BCO guide encourages tenants to install local task lighting if needed and CIBSE LG7 states “200 lux general lighting plus 100 lux task lighting in an office which is purely used for screen-based work (resulting in 300 lux on the task area) is a good balance.”

Shedding embodied carbon

LETI highlights that building services account for 15% of the embodied carbon in a new office. This proportion is higher in refurbishments, and lighting is a significant contributor, particularly when 30-50% of lighting might be stripped out during the initial fit-out. Whilst task lighting is mobile and adaptable, fixed overhead lighting is most likely to become aesthetically outdated and replaced prematurely as part of office churn and at lease expiry.

Although replacement of lighting can single-handedly rejuvenate the perception of a space, its early replacement has a significant embodied carbon footprint penalty. Designing at lower lux levels, however, is beneficial not only for cutting operational energy but also for reducing embodied carbon and cost too if we reduce the number of fittings we install.

Waterman’s study

Waterman’s sustainability team reviewed the embodied carbon savings achieved byreducing design office lux levels and demonstrated that the quantum of fittings can be reduced by as much as 30%. At a reduced 300 lux, the lighting power consumption was below the LETI recommended target of 4.5W/m2 achieving 3.7W/m2 compared to 5.8W/m2 at 500 lux. With 30% of desks provided with LED task lighting for intermittent use, operational carbon can be cut by over a third.

For our notional 784 sqm office this equated to 12 tonnes of tCO2e over a 10-year period – an average of 15kg CO2e /m2 operational CO2 saving. Even with the desk lamps considered, a 20% reduction in embodied carbon (1.87 tCO2e) was achieved, albeit without factoring the impact of waste through stripping out light fittings during office Cat B fit-outs and churn.

In summary, whilst a simple reduction in light fittings may have a relatively small initial impact on cutting a building’s embodied carbon, once factored in with the drop in waste through life cycle churn and through the reduced maintenance associated with lamp and light fitting replacements, the whole-life carbon savings are far more significant.

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