• 19 May 2020

Shedding Light on Whole-Life Carbon

Waterman’s Sustainability experts assess the impact of reducing lighting levels in the workplace.

For many years both the British Council for Offices (BCO) and the Chartered Institute of Building Services Engineers (CIBSE) have provided clear recommendations on lighting levels for offices yet there remains a trend amongst workplace designers to over light the spaces in which we work.

The CIBSE/SLL Lighting Guide LG7 and BCO Guide 2019 both state that a design illumination of 300 lux is acceptable for screen-based tasks, see Fig 1. Computers, tablets, and smart phones provide their own back-lit light source, so we need less ambient light when using them. For most of us this means that we can carry out the large proportion of day to day activities at work with lighting levels of 300 lux. Higher levels only become necessary in areas of the office where specific paper based or fine detail tasks are undertaken. This is certainly not the norm for most office functions these days with the advent of the ‘paperless office’.

The Changing Workplace

The design of our office spaces has evolved considerably over the last decade and we will face a rapid change post Covid-19. What is clear however, is that the use of tablets and touchscreen computers will be on the up as the necessity for mobility and flexibility to choose between home and office working becomes the new norm.

Even in densely occupied offices the actual desk surface area in our workplaces is typically only 10% to 14% of the lettable floor plate, so the energy we waste lighting circulation space is considerable. The impact of Covid-19 on reducing occupancy density will mean that this percentage will drop even further. Whilst heat mapping of occupants to tune light levels is one potential solution to avoiding over-lit offices, task lighting also has a role to play in dealing with requirements for localised increased lighting levels.

There is still reticence amongst speculative commercial office developers, end users and designers to cut the levels of light installed through the overhead lighting. This is primarily due to the perception that reliance on a tenant installing lighting to suit specific tasks would be perceived negatively and reduced illuminance may have a detrimental effect on the marketability of their asset. The BCO guide encourages the provision of power for tenants to install local task lighting should it be needed and with the development of ‘Power over Ethernet’, installing task lighting is simplified even further. The adequacy of lower lighting levels in our workplace is reinforced in CIBSE LG7 which notes that “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.”

New metrics for the built environment

As we move into a new era for the built environment, the way we perceive and value our buildings is changing. The highest technical specification no longer guarantees the most rental value. Instead, Operational and Embodied Carbon are now becoming important metrics in property, kicking the way we conventionally value our buildings into touch.

By designing to 300 lux rather than 500 lux, power consumption is cut proportionally. Lighting energy use can be reduced by of over a third through the implementation of lower light levels in conjunction with localised task lighting where needed. Coupled with adaptive lighting control which has the potential to cut energy consumption by 40% on its own, the savings can be even greater. Reduced lighting levels cut cooling energy use as well. With lighting typically accounting for over a quarter of an office buildings energy use, the impact on operational carbon emissions is clearly significant but the benefit doesn’t stop there.

Shedding embodied carbon

LETI highlights that building services accounts for 15% of the embodied carbon in a new build commercial office. Clearly, this proportion is much greater in refurbishments and lighting is an important contributor to this figure, particularly when we factor that as much as 30-50% of installed lighting in an open plan office might be stripped out during the initial fit-out. This is key when considering a buildings whole-life carbon. Whilst task lighting is mobile and adaptable to change, fixed overhead lighting is most likely to be replaced as part of office churn, layout alterations including floor plates being reverted to open plan for re-letting at lease expiry.

For building services, lighting is generally the element most likely to be prematurely replaced before the end of its economic life span because it is most susceptible to becoming aesthetically outdated. Whilst replacement of lighting can single-handedly rejuvenate the perception of a space its replacement has a significant carbon footprint penalty. The manufacturing process of office light fittings from production of raw materials, manufacture of the multiple components, transportation and ultimately disposal/recycling etc makes them very carbon intensive.

So, designing at lower lux levels is beneficial not only in cutting operational energy but it will reduce embodied carbon and cost too if we reduce the number of fittings we install.

Waterman’s study

Waterman’s sustainability team led by Mark Terndrup and Chloe Souque reviewed the potential for embodied carbon savings through the reduction in design lux levels in a typical office space. The study showed that for a typical office floor with lighting set at 2.8m above floor level, the quantum of fittings can be reduced by as much as 30%. We considered high efficiency 24W 600mm x 600mm LED light fittings supplemented with 9W perimeter LED downlights to represent a typical office layout. It was demonstrated that at 300 lux the installed overhead lighting power consumption surpassed the LETI recommended target of 4.5W/m2 achieving 3.7W/m2 compared to 5.8W/m2 at 500 lux. The quantum of fittings dropped from 225 to 156 over a 784 m2 floor area, see Figure 2 and 3.

Clearly the 30% reduction in light fittings is only realised when compared to the illuminance levels at the upper band of 500 lux. However, even with typical projects designed at 400-450 lux, benefits will be achieved by dropping the design lighting level. Whilst it may be argued that this simple analysis needs to take into consideration the embodied carbon of the desktop lamps this becomes very subjective. Most office tasks don’t require an elevated illuminance level and the need for task lighting is likely to fall. In our route to Net Zero it is far better to minimise the materials we initially install in buildings – we should only add them when needed with desktop lightings only provided to employees who request them.

Waterman’s study concluded that even with 30% of desks provided with LED task lighting with intermittent use, operational carbon can be cut by over a third. For our notional 784m2 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 for the same scenario – this was without factoring the impact of wastage through stripping out light fittings during office Cat B fit-out’s and churn.

A holistic approach to minimising whole-life carbon

Although a simple reduction in light fittings may have a relatively small initial impact on cutting a buildings embodied carbon, once factored in with the drop in wastage through life cycle change and through the reduced ongoing maintenance associated with lamp/light fitting replacements, the savings are far more significant. This aspect is particularly relevant for LED lighting because when faults occur with LED boards or drivers there is tendency for complete fittings to be replaced rather than the individual components. When coupled with other carbon cutting approaches such as underfloor air distribution (read our article ‘Less is More’), the holistic approach to minimising materials use is truly beneficial.

Even though industry standards confirm that reduced illuminance for the screen-based work is acceptable there is a need to convince those involved in development and design that this is not only an appropriate approach, it brings many positive benefits too. Designing at 300 lux provides adequate flexibility and comfort for the office worker and reduces whole life carbon.

Mark Terndrup said: “With an increasing focus on wellbeing, the use of task lighting where it’s needed should be given a greater emphasis in our designs. User control of lighting is already awarded credits by LEED and there is a recognised betterment in wellness through offering people the ability control their local environment. Adding the benefit of delivering whole life carbon reductions through shedding the amount of overhead lighting we install makes the need to adapt our approach to office lighting very compelling.”

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