LED Street Lighting Is Brighter, Bluer, and Increasing Environmental Risk

A new analysis of photographs from the International Space Station demonstrated that upgrading outdoor lighting from relatively warm high-pressure sodium to cooler LED fixtures resulted in increased light levels and a spectral shift to bluer light. The University of Exeter study, published in Science Advances, finds that "this trend is widely increasing the risk of harmful effects to ecosystems."

Previous studies looked at the effects of LED streetlights on bats and insects, and past analyses of satellite photos showed increases in lit area and brightness.

The University of Exeter study compared photos of Europe taken in 2013 when fixtures were predominantly high-pressure sodium and mercury vapor to pictures in 2020 when many countries had converted to more efficient LEDs.

LED street lights are "phosphoric," with blue LEDs exciting a yellow phosphor, and the color temperature is determined by a mix of blue and yellow. Sunlight is very cool light and we see best under it; that's how our eyes evolved. So it made sense that people thought that was best for streetlights, which were designed to put a premium on visual acuity and being able to read license plates. Phosphor mixes can be adjusted to different colors but the cooler, bluer lights are cheaper and more efficient.

The recent study also confirms a point that was very controversial on Treehugger: English economist William Stanley Jevons is at work here.

"While the LED lighting revolution was promoted as being intended to reduce energy consumption, at national or regional scales, emissions (and likely also energy consumption) have increased. One potential explanation of this is that conversion to LED street lighting was associated with adoption of a European standard that led to brighter lighting. Another possibility is the existence of a 'rebound effect' or 'Jevon’s paradox' in outdoor lighting, where increases in power efficiency and the associated perceived decrease in economic cost have driven increased demand for lighting, and hence, any efficiency gains have been counteracted by increased consumption of light."

The study looked at the effects of the blue shift and the increased brightness on the suppression of melatonin, the visibility of stars, and the impact on insects.

Melatonin cycles are key drivers of our biological clock. "Blue-rich LED streetlights operate at a wavelength that most adversely suppresses melatonin during night," said the American Medical Association. It is estimated that white LED lamps have five times greater impact on circadian sleep rhythms than conventional street lamps." The study finds that the level of melatonin suppression "has increased across Europe between the two periods."

With respect to starlight, the study noted, "Along with other animals, humans have long used the stars for navigation, but in modern societies, more critical is the concern that loss of views of the natural night sky may have impacts on people’s sense of 'nature' and of their place in the universe, as well as impacts on astronomical observations." The researchers found a significant worsening of the visibility of stars, although Elon Musk can also be blamed for some of that.

The increases in emissions at blue wavelengths altered the phototaxic response—the bodily movement towards or away from lights and affected the geographic ranges of bats.

The study concluded that the earlier satellite studies may have underestimated the increase in the intensity of lighting because they missed the change in color temperature. "This is a simple outcome of the spectral sensitivity of the associated sensors," wrote the author of the study. They noted this has important implications because the data were used to measure population density, urbanization, economic activity, wilderness areas, and even the impact of the pandemic. They also suggest that the biological impacts are underestimated.

"Last, we show that another consequence of the recent increased whitening of artificial nighttime lighting emissions across much of Europe has been an increased likelihood of negative biological impacts of that lighting. We have focused on estimating these impacts on a few key responses (melatonin suppression, visibility of starlight, phototaxis, and behavior of bats). However, these impacts will be much more extensive than these examples, given that very many biological phenomena are spectrally dependent on and often particularly sensitive to blue emissions."

It should be noted that these problems are relatively easy to fix. A town in the Netherlands cooked up a bat-friendly mix of LEDs that are mostly red, and the major lighting companies all provide warmer fixtures that are properly shielded—it's just a matter now of specifying the right fixtures.

Soon they might all be smart, connected streetlights that have RGB LEDs that can change color and brightness on demand. Often the lights are cranked up because people think they increase safety, but a British study found reducing light levels did not result in any increase in crime or the rate of traffic collisions.

That's why this study is important: It's rare that we get to write about problems that are so easily solved, but people have to know that there is a problem in the first place.