Energy-efficient LED street lights can be garishly bright (Image: Mario Anzoui/Reuters/Corbis)

The roll-out of cheap energy-saving street lights with a bluish glare has little regard for people or wildlife. There is a better way, says Jeff Hecht

This month three men shared the Nobel prize in physics for their invention of blue light-emitting diodes (LEDs). In its citation, the Nobel committee declared: “Incandescent light bulbs lit the 20th century; the 21st century will be lit by LED lamps.”

It’s already happening. Not just in our houses, but increasingly outside too. LED street lights, which are being fitted in cities in many countries, seem like a good idea, because of their energy efficiency.


But then I came home to Newton, Massachusetts, from a holiday to find the ugly reality glaring at me. Scattered light washed out all but two stars in the night sky, and harsh white light cast stark shadows on my porch. I was stunned and dismayed. Why should energy-efficient lighting make the world look garishly bluish-white and bright?

I saw no indication of this when I installed LED bulbs indoors. Manufacturers sought to please the customer’s eye, adding phosphors that converted most of the blue light into yellow and red to give a glow similar to the warm white of an incandescent bulb.

Light currency

But outdoors, the US Department of Energy is pushing LEDs only as cost-effective lower energy lighting. Its municipal street-lighting consortium web page focuses on savings in dollars and lighting intensity in foot-candles (visible light per unit area) not colour ambience. The bluer the output, the greater the intensity perceived by the eye, so that’s what we get. LEDs can also spread light more evenly than older bulbs, because they can contain many small light emitters pointing in different directions.

But those benefits have costs. One is a blue-rich colour mix like moonlight or bright daylight, which many people find unpleasant at night. Glare is another, because “each little LED [in a street light] is one-sixth as bright as the sun”, says James Benya, a lighting designer in Davis, California, where LEDs have provoked protest. The tiny LEDs on the edges of a lamp point outward to spread light across the street, creating glare for pedestrians and drivers.

That glare also shines into homes and gardens. Light trespass is a key factor behind protests in cities from Davis to Cambridge, Massachusetts, and in UK towns and cities. Studies of the impact of LED street lights are under way in many other countries, including Germany and the Netherlands. Pilots have also warned that LEDs being tested for runways produce dangerous glare.

Light sleep

A further concern is that LEDs will worsen excess artificial light at night. Air scatters blue light more than other colours, making the night sky so bright it washes out the stars. Blue light can also suppress melatonin production in humans and animals, affecting sleep and behaviour. The International Dark-Sky Association recommends that outdoor lights should use the same reduced-blue LEDs as indoors.

Of course LEDs have advantages. Unlike high-pressure sodium lamps, they can be instantly turned on and off or dimmed. Moreover, our night vision is more sensitive to blue light than to red, so bluish LEDs allow the same visibility with lower illumination levels than redder lights. But most cities use LEDs at the brighter illumination recommended for the bulbs they replace, wasting energy and increasing the negative impacts.

The challenge is to balance the trade-offs between energy efficiency and environmental impact before the roll-out of LEDs outdoors gets any bigger. In my city, officials have offered to adjust the ones near my house to reduce light shining in the windows, but if they had waited for better bulbs it would have saved time, money and aggravation.