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This section contains reports and articles on Crime and Safety. Everyone expects lighting to reduce crime and increase safety. However if lighting is poorly designed or installed, it can have the opposite affect.

A straight forward application of "Lighting Standards" can result in hazardous situations. Good engineering judgement and common sense must be used in the selection and installation of lights. Otherwise, expensive light installations will produce less than desirable affects.

Crime

There are lots of stories (good and bad) about how crime is encouraged by less light and how crime is deterred by good light. Here is a link from Indiana, USA. It provides links to studies that have addressed the myths and studies into this topic.

Indiana Council on Outdoor Lighting Education

There are an increasing number of articles about the decoupling of crime and light. It should be pointed out that "good" lighting can reduce crime. However, increasing illumination levels and increasing glare do not seem to reduce crime. Here is an article from an Iowa newspaper.

If you know of other studies that are available on the www. Please let us know so that we may review and post them as well.

Safety

Many street light designs and installations help motorists and pedestrians see and navigate at night. However, less than optimal driving conditions or poor visibility can make otherwise adequate lighting hazardous. These may be traced to:

  • rain,
  • dirty and pitted windshields,
  • rain-speckled eyeglasses,
  • poor eye glass perscriptions, and
  • general reduction in visual acquity with age or illness.  

The article Older Drivers' Vision Woes Studied was published by United Press International (Copyright © 1999). It points out a few of the unalterable affects of aging on our sight. The elderly are affected by poor lighting and glare, more than the "typical" citizen. However as we live longer, our average population is becoming older. More attention must be paid to the problem of poor lighting. Most would agree that installing glare-free lighting will help prevent accidents now and long into the future.

Information about problems with poor lighting come from those how have to "pick up the pieces". This second item is a more detailed report on the subject of visibility for motorists. It is rather long and technical so, start with the introduction. Here is a summary:

National Highway Traffic Safety Administration, NHTSA: Dark Adaptation and Glare Sensitivity.

Summary
Although intersection lighting installations are common in many suburban and most urban locations, rural and/or residential settings may contain unlit intersections, and drivers' dark adaption capabilities may be tested in transitions between lit and unlit areas as well. Tests of dark adaptation of the rod and cone photoreceptors in the retina of the eye measure the time course of the improvement in threshold sensitivity with cumulative time in the dark. The normal function for a young adult shows a rapid fall in the threshold for the first few minutes followed by a brief leveling out to the cone plateau, and is then followed by a second rapid drop over 10 or 15 minutes to effectively reach the rod plateau after about 30 minutes in the dark. However, many studies have shown a progressive elevation of both rod and cone thresholds with age (McFarland, Domey, Warren and Ward, 1960; Pitts, 1982), with an accelerated loss above the age of 60 which appears to parallel the increase in lens density documented earlier in this review.

One study found that the elevation in dark-adapted thresholds with age was greatest for shorter (blue) compared to longer wavelengths, and was able to account for most of this difference in terms of increased lens density (McFarland et al., 1960). That lens density contributed strongly to the elevated thresholds in this study was demonstrated by a control group of aphakic subjects who showed approximately 1 log unit more sensitivity than their natural-lens age mates (out of a 1.3 log unit difference); the remaining 0.3 log unit difference could be accounted for by pupillary and neural changes. Similarly, an earlier review concluded that about 1.5 log units out of a total threshold elevation of 2.0 from 20 to 70 years of age can be accounted for primarily by changes in the lens (1.2 log units), and somewhat less by pupillary changes (Kahn et al., 1977).

The impact for the older driver of lost sensitivity under nighttime conditions should be assessed against the nature of the night driving task. Even at night, most visual information is processed by the cone or daylight system in the foveal region; artificial lighting raises the illumination level to the photopic range so that reading and tracking functions can occur. The peripheral rod system participates primarily by alerting the driver to a weaker signal away from the foveal line of sight that may then be oriented to, with the foveal cones. The implication of a loss in rod sensitivity is that a much brighter peripheral signal will be needed to elicit proper visual attention from the driver, and that signals now falling below threshold will be ignored. In fact, the signal may need to be 10 to as much as 100 times brighter, depending on driver age and object color. Since both rod and cone thresholds increase with age, it is also true that more light will be needed to bring important tasks such as reading and tracking (path maintenance) above the cone limit. Indeed, for steadily-increasing numbers of normatively aged drivers, objects depending on reflected light for driver detection may fall close to the elevated cone threshold.

This disadvantage for the older motorist can be further compounded by environmental and/or operational conditions, and age differences in glare sensitivity and glare recovery which penalize this group. First, the stray light introduced into a driver's eyes from roadway glare sources--most notably oncoming vehicles--can create special problems for older individuals. At intersections, additional light from roadside sources and even traffic signals can create glare problems for older drivers. At relatively low pavement luminance levels, glare--or, more specifically, veiling luminance--can be treated as a contrast sensitivity reduction factor, and its effect can be compared with the direct effect of age on contrast sensitivity noted earlier.

In summary, between ages 20 and 70, aging directly reduces contrast sensitivity by a factor of about 3; older drivers are thus at a greater relative disadvantage at lower luminance levels than younger drivers. At the same time, the magnitude of the "glare factor" with respect to its detrimental effect on a 20-year-old versus a 70-year-old driver increases by a factor of about two. Assuming that the effects of age and glare on contrast sensitivity are independent, older drivers are "very" much at a disadvantage in (night) driving situations in which glare is prevalent (Farber and Matle, 1989). A study of age and the brightness of pavement edge lines referenced earlier reported that an older driver test group required a contrast of 20 percent higher than a younger group to correctly discriminate roadway heading (Staplin et al., 1990); adding glare to the identical test protocol magnified the difference in performance between the two groups, and it was observed that glare limited the ability of the older group to discriminate direction-of-curve as a function of distance to the point of curvature, but not the younger group.