Three ways to use human-centric lighting in offices

Previous Design Clinics have described different ways of lighting an office. We have also reviewed colour tunable luminaires, albeit quite some time ago. Since then, both the technology and our knowledge of the effects of changing colour temperature and illumination level on our well-being have come together. These, and other factors, combine to form the human-centric lighting, HCL, approach to office design.

There is not the space here to describe in detail the many aspects of HCL design. In essence, the idea is to synchronise the lighting with our circadian rhythms, or even to modify them -  for example, using artificial lighting to reduce the effects of jet lag. These techniques are often described as biodynamic lighting. There is still a lot more research that needs to be done especially in actually quantifying the cause and effects.  

However, what is certain is that there are three inter-dependent parameters which control the effect of light on humans. The first is the spectrum and it is well established that the blue wavelengths are the biologically active parts. The illuminance level, often referred to as “intensity” in HCL literature, also plays an important part. However, illuminance is always closely connected with the timing, duration and previous history/adaptation state.

This Design Clinic shows three ways of lighting a medium-size office using an HCL approach. It is important to mention that all these schemes meet the recommendations of EN 12464-1. They also include energy saving measures such as presence detectors and daylight harvesting to meet LENI targets.

All three schemes have decent vertical illumination (cylindrical illuminance is the term used in EN 12464-1) which is good for people’s faces and making the space look light and airy.  

The office is approximately 8m x 10m with a 3.5m ceiling. We have designed to a task illuminance of 500 lx and proportionately less for the surround and background. Of course, it is quite possible that having evaluated the tasks involved, you design to a lower task illuminance of 300 lux.

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This option provides the most individual control. The Linea free-standing unit can easily be moved to suit changes in the office layout. Typically, one Linea would illuminate one or two workstations. The light distribution is 75% upwards and 25% downwards and these can be separately controlled by switches mounted on the shaft. The Linea can also vary the CCT from 3000K to 6000K.

The large amount of upward light means that the ceiling is very well illuminated and this “lifts” the appearance of the space. At the same time, there is plenty of light on the task area since the low-glare prismatic optics are adjacent to the desk.

Being able to switch individual luminaires is ideal in offices which are not fully occupied all of the time, for example in hot desking environments. There would be sufficient illumination from just a few Linea to provide background lighting to the whole office.

Tech spec
  • Luminaires Linea free-standing, direct/indirect
  • Light source LED 3000K-6000K
  • Optical control
  • Micro-cone and micro-prismatic panels
  • Arrangement
  • At each desk
  • Average illuminance
  • In accordance with EN 12464
  • Electrical load
  • 5.6 W/m2 at 100% output
  • Pros
  • Individual control
  • Cons
  • Works better with medium height ceilings

This option uses recessed 600 mm x 600 mm panels with micro-prismatic optical control. The Modul-R luminaire is DALI controlled and can vary the CCT from 2500K to 7000K with an Ra >90.

The advantage of this type of scheme is that it can be fully automated to vary the illuminance and CCT throughout the day. The whole space is brightly lit and the ceiling and walls are fairly uniform.

Some personal control of the lighting is always desirable and here we have added the Split desk lamp. This achieves much more light output than most desk lamps and provides a wide spread of light across the whole task area.

As well as being dimmable, one neat aspect of the Split desk lamp is that it is available with a motion sensor that automatically switches it off after 15 minutes of inactivity.

Tech spec
  • LuminairesModul-R 600 mm x 600 mm recessed panel plus Split desk lamp
  • Light source LED panel 2500K – 7000K, Desk lamp 3000K, CRI 90
  • Optical control
  • Micro-prismatic panel
  • Arrangement
  • 3 x 3
  • Average illuminance
  • In accordance with EN 12464
  • Electrical load
  • 7.8 W/m2 at 100% output
  • Pros
  • Can be fully automated
  • Cons
  • Less individual control

 

Suspended direct/indirect schemes are one of my favourite ways to light an office. They work best with ceiling heights greater than 2.5m. The Reed luminaire was originally a highly effective T5 unit and has now been upgraded to LED with variable CCT.

The lighting control system is automated to vary the illuminance and CCT throughout the day. Of course, with any HCL design, you need to speak to the users of the space to determine their visual needs. The type of work involved and the operating hours of the office also need to be considered.

A typical example of this approach might be to provide 500 lux during the morning and mid-afternoon (when people often feel tired) with a Cool CCT of 6000K (pictured above). At lunchtime and late afternoon both the illuminance and CCT might be reduced to maybe 350 lux and 3000K (pictured below). 

Tech spec
  • Luminaires Reed suspended direct/indirect
  • Light source LED 3000K – 6000K
  • Optical control
  • Specular silver reflector plus micro-prismatic lenses
  • Arrangement
  • As shown
  • Average illuminance
  • 300 lux - > 500 lux
  • Electrical load
  • 5.5 W/m2 at 100% output
  • Pros
  • Light and airy
  • Cons
  • Works better with medium height ceilings

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