Three ways to light an office

If you really want to save energy on office lighting, you should make friends with BS EN 12464. Improvements in efficiency can only go so far – the real savings are made by considering the office as a whole: what work goes on, where and when it’s done.

If EN 12464 seems too technical, get a copy of the SLL Code for Lighting or the British Council for Offices’ guide to lighting (see page 60). Both are easy to read and not only help you meet the standards but also to avoid some of the pitfalls like discomfort glare or dark ceilings.

In comparison with a ‘standard solution’ of 4 x 14W recessed unit producing a blanket 500 lx everywhere, we have reduced the energy consumption by over half, in some cases almost two thirds, simply by intelligent positioning of the luminaires. All the schemes have decent vertical illumination (cylindrical illuminance is the term used in EN 12464) which is good for people’s faces and making the space look light and airy without it being too bland.

One final point, although the installed load is halved, we could make further energy savings by using controls such as daylight sensors near the windows. We could also use presence detection units and give people local control to save even more energy.

The office is approximately 9m x 10m with a 3m ceiling. We have designed to a task illuminance of 500 lx and proportionately less for the surround and background.

Trilux's Belviso family is a huge range of thematically similar luminaires and here we have used some free-standing uplights in combination with some shallow surface mounted 600 x 600 modules. Both are LED.

The surface mounted module is used to give a general background illuminance. It is fitted with a fine micro- prismatic lens which keeps the luminance below 1,500cd/m2 so you can use it over VDU workstations. This unit also has a coloured light frame to enliven the ubiquitous white and grey landscape of most office ceilings.

To increase the level of illumination on the task and it surrounding areas, we have some free-standing Belviso units. These, again, are fitted with micro-prismatic lenses and the luminance is even lower at under 1,000cd/m2. The up and down component of these units are separately dimmable giving the office user total local control. 

TECH SPEC

Luminaires Belviso surface mount and free-standing
Optical control Various
Arrangement Three free-standing plus four ceiling units
Average illuminance In accordance with EN 12464
Electrical load 5.4W/m2
Typical cost £5,200
Pros Very flexible layout
Cons Needs a power outlet on floor or desk

The Aurista is one of my favourites in the Trilux range because it adds a bit of interest to the ceiling and gets away from the regular array of slabs of light so often seen in offices nowadays.

The light is emitted from square pyramid shaped reflectors which give a ‘star’ appearance to the luminaire. Each star has 7–8W of LEDs. What is really novel is that the Aurista can be supplied with different numbers of stars from three to seven. The lumen output of the luminaire can thus suit the area in which it is being used.

We have used five-star versions over the main working area and three-star versions over the occasional desks and circulation areas. By designing the lighting layout to suit the space, we have reduced the electrical load to just 4w/m2. 

TECH SPEC

Luminaires Eleven Aurista fittings with varying quantities of LEDs
Optical control Specular reflector and light guide
Arrangement As shown
Average illuminance In accordance with EN 12464
Electrical load 3.8W/m2
Typical cost £1,650
Pros Lively appearance to the ceiling
Cons Darker in the upper region of the office 

Good lighting in British offices is hobbled by our 2.4m ceilings. Design Clinic’s example office does not have this restraint, so we can use a suspended direct/indirect luminaire and achieve a light and airy feel to the space. The body of
the Luceo is just 24mm deep. The semi-specular, 98 per cent reflective cross-blades ensure a luminance of less than 1,000 cd/m2 below 65 degrees, so you can use it in just about any installation with computer screens. We have positioned
them in a three ‘spoke’ arrangement over the desks. This gives plenty of light where it is needed and, because of the reflected light off the ceiling, it gradually reduces towards the office walls. The beauty of this scheme, apart from being the lowest cost, is that there is plenty of light on the ceiling. This, in turn, gives good illumination on people’s faces and meets the often forgotten requirement of cylindrical illuminance mentioned in EN 12464. 

TECH SPEC

Luminaires Nine Luceo 35W T5
Optical control Direct/ Indirect
Arrangement As shown
Average illuminance 400lx on task and proportionately lower elsewhere.
Electrical load 3.8W/m2
Typical cost £1,250
Pros Lots of light on the ceiling and an interesting “star” arrangement 
Cons Ultimately, T5 will disappear