Published 15 October 2020 by Benjamin Skuse
White LEDs: When Good Tech is Applied Badly
How can a technology at least ten times longer lasting and half as power hungry as its rivals be accused of being eco-unfriendly?
In the 1970s and 80s, light-emitting diodes (LEDs) were illuminating futuristic displays for digital watches and pocket calculators, and in the early 90s children were blinking with every step made in the heel of popular trainers. But they hadn’t changed the world. Up to then, optics researchers had produced first the red LED in 1962, followed by orange, yellow and green LEDs in the 1970s. Yet the key colour expected to open up a world of new applications remained stubbornly out of reach: blue.
2014 Nobel Prize in Physics was awarded to Hiroshi Amano and Isamu Akasaki, and Shuji Nakamura separately, announced to the world they had invented the high-efficiency blue LED in 1992/3. By growing big enough crystals of semiconductor gallium nitride and stacking them in alternating layers of another semiconductor, they could apply a current to the semiconductor sandwich that emitted light of the long-sought blue hue.
Global Switch to LEDs
LEDs were soon everywhere. This was because blue was the key ingredient for making bright white LEDs, and for combining red, green and blue to produce practically every colour under the Sun. The innovation has since brought colour to our smartphones, TVs and computers, and transformed just about any application needing light.
There seems to be no drawback to replacing incandescent, fluorescent and other bulbs with LEDs: LEDs are more efficient and last longer than any other types of bulbs, and they do not contain any toxic substances. A prime example of their worth is streetlighting: Compared to traditional high-pressure sodium lamp streetlighting, LED streetlamps are just as bright or brighter, but crucially consume half as much power and last at least twice as long, saving cash-strapped councils money and reducing streetlighting’s carbon footprint. For these noble ‘green’ reasons, in the past decade society has seen a global switch of streetlighting to white LEDs.
Dark Side of Light
However, seen from above, LED streetlighting has a darker side. When our cities and towns are photographed from Earth Observation satellites at night, the extent of excessive and inappropriate LED streetlighting is as clear as day. And this artificial light can have serious consequences on a variety of different life on Earth.
Take insects as an example. Though still understudied, researchers are building evidence to suggest white LEDs result in disrupted circadian rhythms, less courtship signalling, more difficulty finding mates and even death, with the authors of one study asserting that the shift from long-wavelength traditional street lamps to broad-spectrum white LEDs “represents an ecological experiment on a global scale, with potentially devastating results”.
Similar evidence is amassing for the deleterious effects of white LEDs on many other species, including humans. Disrupted sleeping patterns, heightened aggression, glare-related car accidents and even tentative links with higher risks of developing cancer have all been reported. It also threatens stargazing. Representing a “cultural loss of unprecedented magnitude,” according to Fabio Falchi, his 2016 study using satellite data uncovered the fact that one-third of humanity can no longer see the glowing band of the Milky Way because of the effects of artificial lighting.
But it doesn’t have to be this way. Beyond adding shields to block output in certain directions, LEDs have two key properties that are not being used to their full extent for streetlighting currently. First, they can be easily dimmed. From Cambridge, MA, to Cambridge, UK, progressive councils are trialling different adaptive streetlighting approaches. Many opt for a simple approach, dimming lights between late night and early morning. Others, who have installed intelligent streetlights, base their dimming policy on level of activity. When a street or path is empty, the lamps give off minimal light, but then rapidly brighten upon detecting a car or someone on an evening walk. Any citizen can ask their local council to dim the streetlights in their area.
Second, LED streetlights don’t have to be white. Thanks to Amano, Akasaki and Nakamura, LEDs can be produced that emit light in a rainbow of different colour options. The city of Tuscon, AZ, was a pioneer in this regard when in 2017 they installed reddish LEDs. These innovative lamps add high-efficiency red-emitting LEDs to standard blue ones with yellow phosphors to give the same warm appearance traditional lamps offer. Crucially, for a city surrounded by some of the most advanced ground telescopes in the world, converting Tucson’s 18,000 sodium lamps to LEDs and introducing a dimming policy actually led to a 7 percent decrease in the city’s upward-directed radiance, reducing the skyglow effect that can scupper astronomical observations.
Tuscon and a growing number of forward-thinking councils around the world prove that LED streetlighting can live up to its eco-friendly credentials, so long as we light the nocturnal world with more care for our environment.