The Right Amount of Light

Aug. 25, 2003
Why Are Offices Still Over-lit?
Poor lighting – it’s one of the things employees complain about the most, yet they rarely have any control over it. Flickering, glare, and just plain over-lighting can keep people from working to their best potential. Additionally, wasted energy and heavy heat loads from direct lighting continually cost companies money. So, why are offices still over-lit?Space DesignLighting is an excellent way to combine a powerful design element with ongoing operating savings. Lights should be specified at the beginning of the project. But, if a lower-quality product ends up at the jobsite, it’s a result of looking at lighting from a first-cost perspective rather than at the life-cycle of the building and the lighting system.Usually, spaces are planned with a 2X4 troffer grid at 8- by 10-feet or a linear system on 12-foot-center spacing. Both these systems provide a uniform aesthetic with 50FC (footcandles) illuminance while using about 1.2 watts per square foot. (To put things in perspective, we are all usually able to read a book under a full moon on a clear night, and that light is less than one FC.)This would be a fine solution, except for a few facts: In today’s computer-intensive workplace, 50FC is too much light. Plus, most office furniture is sold with individual task lighting, which (by the fact of light being “additive”) ends up flooding 60 or 70FC over the worksurface.The BaseWhen a tenant moves into a space, usually the owner has a base building “standard” which most likely consists of 2X4 recessed troffers. Sometimes, there is credit available for an upgrade, but often the owner doesn’t want different systems in the space and won’t accept changes.For people who plan to stay in a space for at least five years, a lighting upgrade will pay for itself within the first year-and-a-half in energy use alone, based on a minimum energy rate of 10 cents/KW/hour. In this real estate market, tenants can call the shots.Taken to TaskKey factors in the office environment are the user and the task. Most people are quite comfortable working in a 30FC environment. However, depending on the task (an accounting group working on paper-based tasks vs. web designers working on VDTs) and the characteristics of the user (age, eye color, hair color, use of prescription glasses, etc.), plus personal preferences of that user, the range is going to be anywhere between 30FC and 60FC.Hall MonitorNo one works in hallways, yet we light all circulation areas to the same level as the workstations. Consider the concept of user-specific lighting – indirect lighting that gives end-users their own individual fixture (this still works out to fewer fixtures than a 2X4 troffer grid). It provides the basic light level, and a movable task light can pump up the footcandles for paperwork. Any spill-light will help illuminate circulation areas and hallways, further reducing excess lighting and the misuse of energy.Wilson Dau is director of lighting solutions at Calgary, Alberta, Canada-based SMED International (

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