The invention that earned a Nobel Prize in Physics.<\/strong> Old sodium vapor lamps, especially low-pressure ones, were \u00a0monochromatic\u00a0 in nature. They emitted light in a very narrow band of the spectrum, resulting in that characteristic and ubiquitous yellow-orange hue that tinted our streets and skies. On the contrary, \u00a0LED lights\u00a0 work in a completely different way.<\/p>\n The breakthrough that earned Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura the 2014 \u00a0Nobel Prize in Physics\u00a0 was the invention of the \u00a0high-efficiency blue LED\u00a0. By combining this blue LED with a phosphor coating, it became possible to generate a bright and affordable white light. This diode is not only more efficient, exceeding \u00a0300 lumens per watt\u00a0, compared to only \u00a016 for an incandescent bulb\u00a0, but it also offers a much broader spectrum of light.<\/p>\n The cities changed color.<\/strong> To the eyes of a night observer in space, cities have transitioned from yellow to a glowing \u00a0bluish white\u00a0. Milan serves as a paradigmatic case: it completed its transition to LED in 2015 and appears in an \u00a0ESA comparison\u00a0 with before-and-after photos taken by astronauts Andr\u00e9 Kuipers and Samantha Cristoforetti. However, it is by no means the only case.<\/p>\n Los Angeles was a pioneering city, having ordered the replacement of \u00a0140,000 streetlights\u00a0 back in 2009. Buenos Aires modernized its lighting with smart LED streetlights between 2013 and 2016. New York finished replacing \u00a0500,000 bulbs\u00a0 in 2023. Barcelona plans to achieve total remote management of public lighting by 2028. Interestingly, \u00a0India\u00a0 has the largest replacement program in the world, with over \u00a013 million LED streetlights\u00a0 already installed.<\/p>\n The B-side of this transformation.<\/strong> Like every revolution, the LED revolution has a \u00a0dark side\u00a0. Light is cheaper, so cities are not only replacing old streetlights but also increasing the number of light points or their intensity. As a result, we find ourselves with a \u00a0brighter planet\u00a0, making it more challenging to escape from \u00a0light pollution\u00a0.<\/p>\n Statistics may suggest otherwise, but it\u2019s crucial to understand that light pollution is measured by satellites, which are partially blind to blue light. Consequently, the actual increase in light pollution, especially that which is perceived by human beings, is much higher than official figures indicate. Furthermore, blue light significantly interferes with our \u00a0biological clock\u00a0, affecting sleep quality and disorienting migratory birds and moths.<\/p>\n The future is adjustable.<\/strong> The solution does not lie in reverting to sodium. The efficiency of LEDs is indisputable. The key, as with any technology, is in its \u00a0application\u00a0. The next phase of this transition is not about merely swapping out bulbs but installing \u00a0smart streetlights\u00a0. It is estimated that nearly one in four streetlights will be smart by 2030. When connected, they can regulate their lumen intensity based on factors such as time of day or traffic conditions, detect failures in real time, and even collect \u00a0environmental data\u00a0.<\/p>\n This remote management will allow one of the new lighting principles to be enacted: using only the necessary light when and where it is needed. Concurrently, innovative solutions have emerged to protect biodiversity, such as streetlights with \u00a0red light\u00a0, which are currently being tested in Nordic cities to avoid disturbing mammals like bats. Furthermore, ideas surrounding \u00a0bioluminescence\u00a0 as an organic source of light generation continue to gain traction, promising minimal environmental impact without any electricity consumption.<\/p>\n![\"Southern](\"https:\/\/teknomers.com\/en\/wp-content\/uploads\/2025\/10\/1760220727_201_The-cities-are-no-longer-yellow.jpeg\")
\n ![\"Southern](\"https:\/\/teknomers.com\/en\/wp-content\/uploads\/2025\/10\/1760220727_201_The-cities-are-no-longer-yellow.jpeg\"\/)
\n Southern Europe in 2025 from the International Space Station. Image: Don Pettit<\/span>\n <\/div>\n<\/p><\/div>\n<\/div>\n