Lighting

A good lighting design considers the various tasks to be performed within the office space and identifies any special lighting considerations (e.g. graphic design work). Typical activities/areas which could need specific lighting and controls strategies may include:

• General office areas
• Areas for specialist computer work such as designing and drawing
• Meeting rooms for presentations
• Entrance and reception areas
• Transient areas such as circulation, storage and WC areas
• Areas for preparing and eating food
• Break out areas
• Back of house and building management areas

CIBSE LG07/15 Lighting Guide 07: Offices provides information on designing for flexibility within office spaces.

In addition to setting the right lighting requirements for different spaces, fluctuating light levels moving between spaces can also impact the visual comfort of occupants and could lead to eye fatigue. Sudden increases and decreases in brightness that can cause a high level of visual discomfort should be avoided. WELL L02 Visual Balance recommend reducing this issues by ensuring:

• Main rooms do not exhibit 10 times greater or lesser luminance than an ancillary space. This is to avoid substantial changes in light levels as occupants move from one space to another. 
• Surfaces do not exhibit 3 times greater or lesser luminance than an adjacent surface. This is to avoid substantial changes in light levels as occupants look around their immediate area.
• Surfaces do not exhibit 10 times greater or lesser luminance than another remote surface in the same room. This is to avoid substantial changes in light levels as occupants look around the room.
• Changes in light levels to 1.5 times higher or lower than initial light levels are carried out over the span of at least 30 minutes in steps or with a smooth transition.
• Uniformity of at least 0.4 is achieved on work planes. 
• One section of the ceiling does not exhibit 10 times greater or lesser luminance than another section of the ceiling in the same room. 

An overview of different areas within an office space can also be found in Space & Layout Planning.

Tailoring illuminance levels to different office activities/areas can create a visually comfortable working environment and avoid occupant eye strain. In addition, light temperature, intensity and colour can have an impact on sleep patterns and mood.

Applying the following best practice principles can inform a lighting design supporting enhanced occupant health, wellbeing and productivity:

• Achieve best practice illuminance levels to industry standards. 
  • Society of Light and Lighting (SLL), Code for Lighting.
  • BS EN 12464-1:2011 Light and lighting. Lighting of work places. Indoor work places 
  • ISO 8995-1:2002 (CIE S 008/E:2001) Lighting of work places -- Part 1: Indoor
• Ensure that all electric lighting achieves a Colour Rendering Index (CRI) of > 90.
• Consider circadian lighting as part of the workplace lighting strategy WELL L03 Circadian Lighting Design recommends 240 EML (218 meloanopic equivalent daylight D65) as best-practice.

Daylight is ranked amongst the five most desired aspects employees seek in an ‘ideal’ workspace. However, almost half (47%) of all office workers are estimated to be working in an environment with no natural light. Research suggests a positive correlation between availability of daylight and enhanced employee performance, creativity and improved sleep patterns, activity and quality of life (Human Space, The Global Impact of Biophillic Design in the Workplace, Impact of Windows and Daylight Exposure on overall health and sleep quality of office workers). 

Best practice measures for consideration when designing for daylight include:

• Positioning desks towards glazed areas. More specifically:
  • WELL L02 sets thresholds of >75% of desks within 7.5m of transparent envelope glazing or atria, and visible light transmittance (VLT) of transparent glazing is greater than 40%.
  • BREEAM Hea01 sets thresholds of 80 & 95% of floor area within 7m of a wall which has a window or permanent opening that provides an adequate view out.
• Provide sufficient window areas. More specifically:
  • BREEAM Hea01 recommends windows or openings must be ≥ 20% of the surrounding wall area. Where the room depth is greater than 8 m, compliance is only possible where the percentage of window or opening is the same as, or greater than, the values in Table 1.0 of Lighting for Buildings: Code of Practice 2008.
  • WELL L02 recommends ensuring window areas are no less than 10% of the regularly occupied floor area, and visible light transmittance (VLT) of transparent glazing is greater than 40%.
• Provide workspaces with a view of the sky. More specifically:
  • BREEAM Hea01 requires 80% of occupied work space.
  • WELL L05 requires requires 50% of occupants.
• Locate transient areas (e.g. printer/copier) and meeting rooms for presentations towards the building core away from glazing and glare.
• Use light-coloured and reflective surface finishes diffuse daylight deeper into the office floor plan.
• Use a computer simulation to demonstrate that spatial daylight autonomy_300/50% (sDA_300/50%) is achieved within a % of occupied space. Rating thresholds typically range between 55% and 75% (WELL L02 & LEED).
• Use daylight modelling to target and prove good daylighting levels. More specifically, BREEAM Hea01 recommends:
  • 80% of the floor area achieves illuminance levels of ≥300 lux from daylight alone for 2000 hours per year.
  • 80% of the floor area achieved a 2% average daylight factor with a uniformity ration of at least 0.4

Refer to the Layout & Space Planning for further consideration of spatial design in relation occupant comfort.

Preventing eye strain and headaches caused by glare and direct sunlight is important for occupants’ visual comfort. Best practice measures for a glare-free working environment include:

• Developing a glare control strategy in tandem with any lighting strategy.
• Ensuring glare reduction measures does not increase energy used for lighting, by maximising the potential for daylight in all weather (overcast or sunny) and ensuring that the location of shading does not conflict with the operation of lighting control.
• Ensure annual sunlight exposure of ASE_1000,250 is achieved for no more than 10% of regularly occupied space. 
• Ensuing 100% of artificial light is emitted above the horizontal plane.
• Require luminaires are installed at a height of 5 m (16 ft) or lower meet UGR of 17 or lower, or, luminaires installed at a height greater than 5 m (16 ft) meet UGR of 20 or lower.
• Avoiding the specification of glossy finishes and surfaces.
• Specifying light-coloured opaque shading devices (e.g. blinds) to prevent direct sunlight, but allow daylight penetration.
• Considering manually or automatically operated blinds to minimise glare.
• Coordinating location of computer screens with lighting and window locations to avoid glare.

The use of low energy lamps and smart controls can reduce electricity consumption by 30% - 60% according to the Carbon Trust, as well as enhance occupant satisfaction and comfort.

The lighting of a fit-out is also a major contributor to a buildings EPC rating, and an important element to mitigating risks associated with Minimum Energy Efficiency Standards - See Owner Benefits.

Best practice measures which could be considered when specifying luminaires and controls include:

• Daylight and occupancy detection sensors to automatically dim and/or switch off lights
• Energy efficient lamps, such as LED lighting, to reduce running and maintenance costs
• Lamps with a minimum efficacy of 60 lumens/circuit Watt (Non-Domestic Building Services Compliance Guide – Section 12 Lighting)
• Setting targets against industry benchmarks. e.g. CIBSE TM37, where typical lighting loads in office areas are:
  • Open plan office: 18.8 W/m2.
  • Meeting Room: 11 W/m2.
  • Reception: 10 W/m2.
• Selecting lamps and control products on the Energy Technology List.

Appropriate zoning of lighting in the workspace can help to ensure efficient operation and good occupant comfort. Best practice principles when creating lighting control zones include:

• Creating separate zones near windows and atria, where artificial lighting is dimmed and/or switched off whenever there is sufficient daylight.
• Servery and dining areas separately zoned.
• Creating lighting control zones by workstation numbers.
  • BREEAM Hea01 requires no more than 4 workstations per zone.
  • Ska D02 Lighitng controllability requires no more than 8 workstations per zone.
• Lights automatically controlled by motion detection (presence/ absence) and the presence of daylight where appropriate.
• Give occupant’s local and manual override of automatic control.
• Maximise flexibility and comfort with multiple control zones in larger meeting rooms.
• Maintain lower overhead illuminance levels and use task lighting focused on the desk area.