Frank Sinatra's In the wee small hours was a concept album full of songs about loneliness and depression; he wanted to title it Songs for Losers. Wikipedia notes that "the cover artwork reflects these themes, portraying Sinatra on an eerie and deserted street awash in blue-tinged street lights." It is an interesting choice, given that street lights at the time were mostly warm yellow incandescent lights. However the artist knew all about blue.
Today, thanks to energy-saving LEDs, our streetlights are actually blue light specials, with a very high colour temperature. Phosphor-converted LEDs (where the light actually comes from an excited phosphor, just like in fluorescent lights) are more efficient in the higher ranges, and the light appears whiter, making it easier to distinguish colours of cars that Police are chasing. Mike also wrote earlier of studies that show pedestrians feel safer with white streetlights.
But according to the American Medical Association, they can be too bright and too white. "Despite the energy efficiency benefits, some LED lights are harmful when used as street lighting."
High-intensity LED lighting designs emit a large amount of blue light that appears white to the naked eye and create worse nighttime glare than conventional lighting. Discomfort and disability from intense, blue-rich LED lighting can decrease visual acuity and safety, resulting in concerns and creating a road hazard.
In addition to its impact on drivers, blue-rich LED streetlights operate at a wavelength that most adversely suppresses melatonin during night. It is estimated that white LED lamps have five times greater impact on circadian sleep rhythms than conventional street lamps. Recent large surveys found that brighter residential nighttime lighting is associated with reduced sleep times, dissatisfaction with sleep quality, excessive sleepiness, impaired daytime functioning and obesity.
Then of course, there is the issue of light pollution; as TreeHugger noted recently, 80% of North Americans can no longer see the Milky Way. We've noted that ", light pollution wreaks all kinds of havoc on the natural world, from affecting birds' nighttime navigation to disorienting baby sea turtles to disrupting the mating patterns of fireflies." The AMA goes further, writing:
The detrimental effects of high-intensity LED lighting are not limited to humans. Excessive outdoor lighting disrupts many species that need a dark environment. For instance, poorly designed LED lighting disorients some bird, insect, turtle and fish species, and U.S. national parks have adopted optimal lighting designs and practices that minimize the effects of light pollution on the environment.... The AMA recommends an intensity threshold for optimal LED lighting that minimizes blue-rich light. The AMA also recommends all LED lighting should be properly shielded to minimize glare and detrimental human health and environmental effects, and consideration should be given to utilize the ability of LED lighting to be dimmed for off-peak time periods.
Perhaps it is time to roll out the next generation of smart, connected streetlights that can be dimmed or that even have RGB LEDs that can adjust for colour, or even just turn on when they detect motion. A British study determined that dimming the lights had little impact on safety:
Researchers looked at 14 years of data from 63 local authorities across England and Wales, searching for trends among agencies that reduced their lighting….That research shows less than 1 percent of all nighttime traffic collisions occurred on streets where the lights had been switched off. And overall, the statistics showed no link between accidents and dimming, reducing, or changing the style of streetlights. Secondly, the researchers looked at lighting’s effect on crime trends. In regions of reduced lighting, they found, there was no increase in burglary, auto theft, robbery, violence, or sexual assault.
Perhaps we would all sleep better, and save a lot of energy, if we listened to the AMA and turned down the lights, and if we put on a happier Frank Sinatra album.