Age, Luminance, and Print Legibility in Homes, Offices, and Public Places

By Charness, Neil; Dijkstra, Katinka | Human Factors, June 1999 | Go to article overview

Age, Luminance, and Print Legibility in Homes, Offices, and Public Places


Charness, Neil, Dijkstra, Katinka, Human Factors


INTRODUCTION

What are typical luminance levels in the built environment? Knowing the answer to this question would be valuable both for experimenters wanting to select representative luminance levels in experiments and for those wanting to determine to what extent actual luminance levels depart from recommended levels provided by bodies such as the Illuminating Engineering Society of North America (IESNA). In addition, such information might have value for researchers investigating seasonal affective disorder (SAD), depression-like symptoms associated with low light levels in winter (e.g., Rosenthal, 1993). Thus one goal of this study was to survey built environments to determine ambient luminance levels.

A second goal was to assess whether ambient light levels in homes vary with the occupant's age. This goal was motivated by the finding that effective light levels diminish significantly with age because of declines in pupillary excursion capability and increasing opacity of the structures through which light passes (Weale, 1963). If older adults attempt to compensate for these changes (e.g., Charness & Bosman, 1995), one would expect to find that they increase light levels in their homes to provide more effective lighting for reading tasks.

Our third goal was to assess whether making changes to ambient light levels might improve legibility performance of older adults differentially compared with younger adults. If light levels follow a law of diminishing returns for performance improvement (e.g., Smith & Rea, 1978), then younger adults should derive less benefit from increases beyond typical ambient levels than do older adults. Aging generally tends to reduce the person-environment fit (Lawton, 1977). Poor fits can occur particularly for lighting and sound, given the strong interactions between age and variables such as light and dark adaptation processes and thresholds for different sound frequencies (Charness & Bosman, 1992, 1994). Given the aging of the workforce (Howell, 1997), it is important to investigate whether improvements in lighting design in workplaces will yield improvements in worker performance, particularly for older workers.

Finally, our fourth goal was to determine what barriers exist for changing lighting in buildings. We provided feedback in the form of recommendations for lighting changes to building managers and followed up 6 months later to see what changes had been made or were planned and what the barriers were to change.

Because we wished to study the natural ecology of lighting, we chose to do field studies. This meant giving up some experimental control but also that observed effects are probably robust. To attempt to partly compensate for this loss of control, we chose to investigate relatively large samples of both environments and participants. In addition, we needed to choose relatively short legibility tasks for determining changes in performance when lighting was manipulated. Ambient light levels can change rapidly during the day between bright sun and cloudy states. Also, tasks can be interrupted in public places (e.g., by bystanders, noise). Because different legibility tasks might tap different aspects of the reading process, we included tasks that assessed different aspects of reading and evaluated their stability and interrelationship.

Tinker (1963) showed that illumination is a much more potent factor for legibility than other factors, such as print size and font type. Table 1 attempts to summarize Tinker's research program. Tinker and colleagues generally used a time-based speed-of-reading measure that required participants to cross out a word in a paragraph that did not make sense. Texts comprised 30 short paragraphs of roughly 30 words each. In general, increasing the level of illumination results in improved visual performance. However, the benefit of increasing illumination follows the law of diminishing returns; subsequent increases result in smaller gains in performance, and, at some point, further increases in illumination do not result in improved performance. …

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