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Eye of the beholder: from office lighting to the famous color-changing dress debate, individual perception is key.

We all develop a mindset based on past experience, so be forewarned that the new ASHRAE/IES 90.1-2016 energy code will use the performance data of LEDs, not fluorescents, to calculate illuminance levels. We now must become more familiar with the latest solid-state lighting products, especially when retrofitting existing facilities.

Peter Jacobson, a lighting specialist at Con Edison, had this suggestion:

"Utilities have contributed by offering customers very healthy incentives to buy down the cost of new technologies. We have a wide range of lamps and luminaires that can replace any existing equipment and save 30 to 75 percent in energy, but we now need to explore further the capabilities and the cost effectiveness of lighting systems and their controls in a new light."

To illustrate our own mindset, we recently recommended that a large underground parking garage with 1,000 8-ft long fluorescent strips, each with an 8-ft long T12 75-W slimline lamp, be retrofitted with 2-4-ft long 15-W T8 LED tube lights, one lamp to be on 24/7, with the other controlled by an occupancy sensor. The facility's chief engineer informed us that their in-house, dual-fuel generators were recently switched from oil to natural gas, lowering their cost to $0.065 per kilowatt hour. This meant that the sensor-controlled LED lamp would not be off long enough to justify the initial cost of the occupancy sensor. This is an example of the results of DOE's net zero energy campaign and the recent increase in the efficacy of LEDs where you have to reevaluate the economics of even using sensor controls.


Office employees' salaries and benefits account for 10 times the cost of renting or owning space, so worker productivity must be enhanced by ergonomic and environmental conditions, not diminished. The National Research Council of Canada's latest report this October advised: "Our work has shown that there are considerable individual differences in light level preferences in offices, meaning that the best way to ensure that people are able to experience their preferences in offices is to provide a degree of individual control."

Every watt in a task light is worth 10 times that amount of power in a ceiling-mounted luminaire in producing light on the desk. Consequently, the most energy conserving office lighting system would be one with an adjustable task light providing two-thirds of the IES Handbook recommended task illuminance, with the balance coming from an ambient light source either at the ceiling, or coming from a desk-mounted task light system with uplight. Some energy codes require that occupancy, vacancy and/or daylight harvesting sensors control ambient lighting, but sensors may no longer be cost effective with lighting power density reduced to 0.5 watts per sq ft or less.

It is now being suggested that we match the color of ambient light in offices to the changing color of daylight, which is not without some peril. Last February, a hot issue in the media was "Dressgate," where a dress was judged by a million observers to be "blue and black," "white and gold," "blue and brown," and "blue and gold." The human eye/brain system evolved to seeing color in a sunlit world, where daylight affects the color of everything and we compensate for the chromatic bias of daylight color. We perceive the color of an object based upon the color context of its surroundings.

Who decides what color of light to choose for the workplace and when? Office planners warn that some people in large open-plan offices are distracted by noise, temperature, humidity and glare, and while collaboration contributes to the interchange of ideas, not everyone is respectful of the privacy that other workers require. Why add another potential distraction?

Marching music is piped into elevators and offices late in the day to enliven everyone from their post-lunch lull. We're acclimated to the sun's daylight color of pinkish red early in the morning and late in the afternoon, but daylight is only blue-white around noon. The lighting equivalent of marching music is blue light, so to pep people up in the late afternoon you must use bluish white light, and not match pinkish red light. Color perception, like beauty, lies in the eyes of the beholder.

Willard L. Warren, PE, Fellow IES, LC, DSA, Is principal of Willard L. Warren Associates.
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Title Annotation:ENERGY ADVISOR
Author:Warren, Willard L.
Publication:LD+A Magazine
Date:Jan 1, 2016
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Next Article:The next generation of occupancy sensing? Two studies point toward more nimble systems for office settings.

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