Like death and taxes, there’s no denying that outdoor lighting has become an inescapable part of life. Streetlights adorn our roads, billboards stud our freeways, shopping-center parking lots are aglow from dusk to dawn, businesses obsess over late-night security, and convenience stores outdazzle one another to compete for customers. We cheat the night of darkness and, in the process, create light pollution that robs the sky of stars.

Electric streetlights have been with us since the 1880s, and it wasn’t long thereafter that some manufacturers recognized the visual and cost-saving benefits of directing light down, onto the ground. In 1918 the Holophane Glass Co. published the very first roadway-lighting manual. Titled The New Era in Street Lighting, it set forth a number of recommended practices, among them the common-sense notion that “Light above the horizontal must be conserved.” In a later section, the manual notes:

In addition to the two fundamental items of highly efficient lamps and the effective use of the light, as discussed, it is very important to see to it that the street lighting system produces an effect which surrounds the eyes of those using the streets with conditions under which the eye is free to perform its functions properly. Any system which fails in this respect is extravagant — no matter how efficient the lamps nor how efficiently the light may be directed upon the street surfaces or objects. Glare serves seriously to reduce the discerning power of the eye.

Unfortunately, almost no one heeded this unsung champion of good lighting practices. Instead, artificial skyglow became markedly more obvious in the late 20th century with the widespread use of high-intensity fixtures utilizing mercury-vapor and high-pressure-sodium lamps, and with a societal shift that found more people on the streets at night — and at later hours — than ever before. As our nocturnal wanderings increased, so too did the need for ubiquitous nighttime illumination. Then decision-makers began to equate “more light” with “better safety and security,” even though objective proof of such a relationship did not exist.

Lighting and Crime

In 1996, at the request of Congress, the National Institute of Justice conducted a landmark assessment of crime and violence in the United States and published the results as Preventing Crime: What Works, What Doesn’t, What’s Promising. The study found little research to support “brighter-is-safer” approaches and even suggested that in some circumstances poorly designed illumination might actually increase personal vulnerability:

The problematic relationship between lighting and crime increases when one considers that offenders need lighting to detect potential targets and low-risk situations. Consider lighting at outside ATM machines, for example. An ATM user might feel safer when the ATM and its immediate surrounding area are well lit. However, this same lighting makes the patron more visible to passing offenders. Whom the lighting serves is unclear.

Vision and safety are further compromised by glare, which results when a light source forces the eye to adapt to a brighter scene than is actually present. Lighting engineers make a distinction between discomfort glare, which may not necessarily affect visual performance, and disability glare, which does. (One example of the latter is what you experience at night from the “high-beam” headlights of an oncoming vehicle.)

In recent years the role of glare on visual performance has taken center stage in lighting research. Nowhere is this truer than within the ranks of the Illuminating Engineering Society of North America, which establishes standards and recommended practices followed by lighting designers and manufacturers. New studies on glare, task-specific lighting, and their environmental context are driving major revisions in the society’s approach to establishing recommendations. “There’s been a profound change in the IESNA,” says James Benya, a nationally recognized lighting professional, and pro-dark-sky principles now dominate the society’s deliberations over outdoor lighting.