Volume 6, Number 4, Fall 2001
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The latest edition of the IESNA Lighting Handbook, published in 2000, contains an important change-a new chapter focusing on lighting design called "Quality of the Visual Environment."
©2000, ILLUMINATING ENGINEERING SOCIETY OF NORTH AMERICA. USED BY PERMISSION.
The Handbook, published by the Illuminating Engineering Society of North America, is the principal source for information about the science and art of lighting, helping lighting designers, engineers, and facilities managers identify their lighting needs and make appropriate lighting choices.
"People misunderstood the previous editions," according to IRC's Jennifer Veitch, a member of the task force that wrote the new chapter. "There was an extensive procedure for calculating illuminance-the quantity of light falling on a surface-which created the erroneous impression that quantity of illumination was the only important criterion for good lighting." The new chapter tackles, instead, the resulting visual environment-vision issues, human factors, task-specific lighting concerns and system integration.
IRC researchers played a large role in developing a model of lighting quality that was eventually incorporated into the Handbook. This model takes into account three critical areas involved in making lighting choices, with an emphasis on the first:
- individual well-being (visibility, task performance, health and safety, mood and comfort, and aesthetics)
- economics (installation, maintenance, operation, energy, and environment), and
- architecture (form, composition, style, codes and standards).
Without a balance among these areas, the value of the lighting choice will be compromised.
The new chapter recognizes the importance of the appropriate quantity of light, but goes far beyond it. "Quantity is really an aspect of quality," confirms Veitch. "If there is not enough light to see important details, then a basic human need has not been met." Seeing small details, however, is not the only purpose for lighting.
Too much light in the wrong places is as detrimental as insufficient lighting. This excessive light, or glare, can be broken down into three separate categories: direct or reflected glare, disability glare and overhead glare. Key elements involved in solving these problems, according to the Handbook, are:
- judicious positioning of computer monitors and choice of luminaires to avoid glare on screens;
- controlled daylight integration to avoid heat gain and excessively high luminance; and
- careful consideration of luminance distribution to avoid both shadows and excessive uniformity.
Lighting should highlight points of interest. "It's a matter of providing higher than average luminance for a particular object while at the same time avoiding glare," says Veitch. Modelling-that is, making the three-dimensional characteristics of objects visible-she notes, is also important; for instance, well-directed light will make faces visible, so that we can see and interpret facial expressions that communicate as much as words.
The Handbook does not leave people to figure out all the issues by themselves. A critical part of the new edition is the Lighting Design Guide, which provides guidance on lighting for specific tasks. This section is organized by type of application:
- sports and recreation
- emergency, safety and security.
These six application types are further broken down by activities, tasks or places. Columns in the table identify lighting design issues and pinpoint those that are most important for a particular application, using colour to code four different levels of importance. In addition, the Lighting Design Guide includes all the necessary definitions as well as annotated illustrations of different types of spaces (e.g., offices, factories).
To determine recommended illuminances for vertical and horizontal surfaces, lighting selection guidelines for various tasks are included, with references to other chapters that can assist designers in choosing the right lighting for the particular circumstances.
The 9th edition of the IESNA Lighting Handbook is available from the Illuminating Engineering Society of North America, http://www.iesna.org.
Specific questions can be directed to Dr. Jennifer Veitch at (613) 993-9671, fax (613) 954-3733, or e-mail email@example.com.