COMMeMOratiVe ISSue - Illuminating Engineering Society

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e s e a r c h M A T T E R S To help the IESNA “celebrate the past and imagine the future,” five scientists from the Lighting Research Center offer their perspectives on where lighting research is headed. John Bullough explores when to use lighting, not just how much; Yukio Akashi explains how research can help drive sustainable design; Mariana Figueiro notes that lighting’s impact goes beyond visible light; Conan O’Rourke looks at the future of fluorescent lighting; and John Van Derlofske says lighting for our roadways must convey meaningful information to drivers. From “How much” to In the century ahead, time will “When” matter in research and application. John D. Bullough Our increasingly brighter nighttime The IESNA has long produced sky, for example, reduces our ability guidelines for lighting in various applications, via its Lighting mining if and when to turn lights to understand our universe; deter- Handbook and recommended practices. Most recommendations focus important question. We know that off outdoors (curfews) will be an on the appropriate quantity of light morning light exposure has a different effect on the human circadian for buildings and roadways. Efforts to quantify the illumination necessary for visual performance filled the tical lighting. [6] Shrinking energy system than night exposure to iden- 20th century. [1-3] Even with recent resources will make controls more efforts in lighting quality, recommendations still use numbers like lation. The IESNA must exercise significant in every lighting instal- luminance ratios. The 20th century wisdom in encouraging research to also taught us that not all footcandles are equivalent. Some lamps lighting is appropriate in the world study when, not only how much, outperform others for rendering colors; life illuminated entirely by low of the next century. pressure sodium, despite its efficacy, [4] would not be so enjoyable. Lighting Towards Sustainable Various color-related indices help us Yukio Akashi understand lighting better than if we In the last century, the effects of know only the quantity. Often, common expectations about appropri- were studied on the basis of bio- light levels on visual performance ate relationships between light and physics. Those studies established color can guide us, evidenced by the models in which visual performance Kruithof curve in today’s Handbook. for a given luminance contrast was More recently, we’ve learned how described as a plateau and an escarpment as a function of illuminance. [1] different lamps outdoors can impact peripheral visibility, even at the same IESNA’s illuminance recommendations are not determined by nighttime level. [5] visual performance alone, but rather are subject to many other forces. [7] Until fluorescent lamps replaced incandescents in the 1940s, practical illuminances tended to fall on the escarpment. Afterward, illuminances reached the plateau, where performance is less sensitive to changes in illuminance. Since then, illuminance standards have been affected by economic and energy concerns. Obviously, sustainable lighting will play a major role in the coming century. One way to facilitate this is to reduce illuminances for regular tasks without impairing visual performance. A recent demonstration study using a simple retrofit task-ambient lighting technique addressed this question. [8] This demonstration study reduced ambient illuminance by removing one lamp from every three-lamp fixture while maintaining task illuminance. This de-lamping resulted in a change in ambient illuminance from 550 lx to 350 lx. Workers accepted this illuminance reduction after a short period, although they initially did not prefer it. The same demonstration study suggested that the use of a lamp with relatively more short-wavelength components significantly helped maintain room brightness. Room brightness is an essential element of lighting quality, as many studies have suggested. [9] To further facilitate acceptance of sustainable lighting design for new construction and other applications, we must implement measures that enhance room brightness while 30 www.iesna.org
R E S E A R C H M AT T E R S lowering illuminance. [10] Thus, the true measure of sustainable lighting might be showing that we can have the best of both worlds—that is, we can have acceptable brightness and lower illuminance. Research that bears this out could go a long way toward helping sustainable lighting gain widespread acceptance. Health and Well-being Mariana G. Figueiro Over the past century, much research has focused on understanding how lighting affects human health and well-being. Lewy et al. [11] began this trend with the discovery that bright white light ceased nighttime production of the hormone melatonin. More recently, a clearer understanding has emerged about light’s characteristics affecting the circadian system. These differ considerably from those affecting the visual system. [12-14] The discovery of a novel photoreceptor in the eye [15] was a breakthrough, and we now know that white (polychromatic) light is a relatively weaker circadian stimulus than blue (nearly monochromatic) light. [16-18] In the next century, we will need to understand better the temporal characteristics of light exposure and their effects on the circadian system. We will also need to quantify the magnitude of light’s effects on the circadian system in different contexts. We must translate findings from animal models to humans appropriately, and we must better understand the robustness of light’s effect on the human circadian system in environments where light is applied. We have found robust, positive effects of light on sleep quality and rest/activity rhythms in some populations (e.g., older adults [19] , Alzheimer’s disease patients [20] and premature infants. [21] ) However, it is not completely clear how light affects others. The effects of electric light on farmers, for example, will likely differ from those on computer-aided draftspersons. We must understand the contextual effects of light before anyone can judge how light impacts human health and well-being. Fluorescent Technology Conan O’Rourke The last 100 years encompasses the entire history of fluorescent lamps, as it does for most light sources. Fluorescent lamps have come to dominate many commercial and industrial applications. In the late 1930s fluorescent lamps became a viable commercial product available in daylight, white, gold, red, blue, pink and green, and had a rated life of 1500 hours. They came in tubular shapes (1 and 1 1/2 in. diameters) and in lengths of 18 to 36 in. The daylight and white lamps had efficacies of 30 to 35 lumens per watt. [22] Over the years there have been advancements in all aspects of lamp design. Today, fluorescent lamps are offered in many shapes and sizes. Lamp diameters have decreased January 2006 31
Page 1 and 2: January 2006 L i g h t i n g D e s
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