Lighting satisfaction is created if a lighting system responds to all the human needs served by light.

Sight is the sense that provides most of our information about conditions around us. Vision shows details, initiates perceptions of space, and contributes to mood, communication and comfort. Satisfaction of an employee's physical and task needs requires good quality lighting and the fulfillment of the many human lighting needs.

People who design lighting systems should understand all the effects of light to create a satisfying lighting system and environment.

Visibility and Task Performance

The Illuminating Engineering Society of North America (IESNA) defines visibility as "the ability to extract information from the field of view" ^[1]. The light level, contrast of object to background, size of object, age of viewer, and length of time viewed determine how much information people receive from their surroundings.

In the office, occupants need enough light to complete their tasks. A poor lighting environment can reduce accuracy, increase the time taken to do a task, and cause fatigue or eyestrain.

No one light level is satisfactory for all activities because an effective light level depends on the visual difficulty of the task and individual preference. It is often most effective to provide multiple light levels in a space or give occupants personal lighting controls so that they can set the appropriate light levels for themselves.

Visual Comfort

A lighting system should provide comfortable, as well as adequate, light. Flickering light, glare, and shadows can make a task difficult and uncomfortable to see, which can negatively affect task performance, health, and safety. If occupants have to strain their eyes to compensate for the poor lighting, they can develop headaches, fatigue, eyestrain, and postural problems (people sit poorly to avoid glare).

Comfortable lighting is not without shadows or changes in light levels. To relax their eyes and take a break, office occupants need some distant areas on which they can focus. These areas can be created by moderate changes in light levels, art work, or views through windows.

Providing visual comfort involves creating a system that avoids glare and shadows, but provides some luminance variation.

Communication

Interpersonal communication relies on visual cues like body language and facial expressions. Harsh light and shadows on the face can distract the viewer or mask these cues. Light from multiple directions give good facial modelling.

Health and Safety

Lighting designers have to consider all the health and safety issues of a space to ensure that dangers are avoidable.

Low-frequency flicker and glare can contribute to headaches, fatigue, eyestrain, and postural problems.

Lighting designers in commercial spaces must also consider lighting for emergencies. Emergency lighting requirements are described in Chapter 29 of the IESNA Handbook (9th edition) ^[2]. These requirements ensure that stairs, obstacles, and exit routes will be visible at all times.

Light also has many non-visual health effects that researchers are just beginning to understand. A separate, but parallel, system of light detection leads to physiological responses to patterns of light and dark and contributes to maintaining circadian rhythms (wake-sleep cycles).

As these effects of light are better understood, lighting practices will have to change to maintain the best health and safety possible. Researchers are beginning to believe that all people require daily doses of light and dark to be healthy. It appears that humans require more light exposure during the daytime and less at night than most people currently get. To allow higher daytime light exposures while achieving good energy-efficiency, the best recommendation for the moment is to use as much daylight as possible to effectively light indoor spaces, instead of concentrating on electric light sources only.

Lighting experts have a responsibility to be aware of new research that may affect light use. The following sources provide further information on these issues: International Commission on Illumination (CIE) (http://www.cie.co.at/cie/), Illuminating Engineering Society of North America (IESNA) (www.iesna.org/), EPRI Lighting Research Office (http://www.epri.com/LRO/).

Mood

Patterns of light in office space contribute to the occupant's state of mind or feelings in the same way light evokes a response on stage or in a movie. For example, a dim space with low contrasts might contribute to feelings of relaxation; a bright space with sparkle could be stimulating. The luminous environment of an office should be designed to enhance occupant mood.

Lighting can also enhance corporate image. Lighting designers need to create an appropriate emotional response with their choice of lighting fixtures, intensities, and colours. Quality office lighting not only provides the information, but also consciously creates impressions.

Aesthetic Judgment

A viewer's aesthetic judgment of a scene responds to impressions of beauty and answers the question: "Do you like this scene and the lighting?" Light that conflicts with the architectural patterns, colour, or meaning of a space can be ugly or uncomfortable. Working under lighting that one likes can improve mood, which contributes to task performance and to the social environment.

Windows: Daylight and View

Both the daylight and the view that windows can provide an increase in environmental satisfaction. COPE found that 96% of people prefer some daylight in their offices, and the COPE field studies found that access to a window was a significant predictor of overall environmental satisfaction. Daylight provides good colour rendering and good modelling, because it hits objects from the sides and top. Windows provide a view, a connection to the outdoors, time and weather information, and distant objects on which to focus for a rest. Both direct or indirect access to a window and its benefits can help to satisfy occupants.

References:

1: Illuminating Engineering Society of North America (IESNA). (2000). The IESNA Lighting Handbook: Reference and Application. 9th edition. Ed M.S. Rea. New York: IESNA. Pg. 10-1.

2: Illuminating Engineering Society of North America (IESNA). (2000). The IESNA Lighting Handbook: Reference and Application. 9th edition. Ed M.S. Rea. New York: IESNA. Chapter 29.