Hi everyone!

In this post, I am going to continue our debate on the benefits and costs of LEDs. In the previous post, we found that LEDs are celebrated as the most energy-efficient bulbs of all time, and are increasingly used as street lighting by cities. However, what are the hidden costs, behind those bright, white lights?

First, we need to talk about the blue wavelengths of light that LEDs emit. You might probably be familiar with the electromagnetic spectrum as shown in the photo below. See how we can only perceive a small part of that spectrum, called visible light? Different bulbs emit different wavelengths of light. Some wavelengths of light, such as blue/purple light, are short, while redder wavelengths of light are long. While LED lights can be configured to emit warmer or cooler light, most LEDs today emit blue wavelengths of light, which measure around 440-500nm. This has negative consequences on our health, and the environment too!

Coinciding with the blue wavelength of light emitted by LEDs, is also the suppression of melatonin production in our bodies. The suppression of melatonin production disrupts our natural circadian rhythms, leading to higher risks of insomnia, stress, illness and even cancer, as reported by a study in the Journal of Environmental Management. (Did you know that your phones, tablets, and computers also emit blue light? Could that also be linked to how we city folks are sleeping later at night, given how long we spend looking at our screens?) Now that’s worrying.

Photo: Getty Images

The diagram below compares the Kelvin colour temperature of different forms of lighting. Compared to other forms of lighting such as metal halide, high-pressure sodium and incandescent bulbs, LEDs emit the bluest light. As much of our street lighting is being converted to LEDs, light pollution is set to increase. The study also reported that blue light is more readily scattered in the atmosphere than red or green light, and that LEDs could produce a growth of artificial night sky brightness by 2.5-5 times, as perceived by the dark adapted human eye.

Photo: LED Spot

So what can we do to prevent the harmful effects of LED lighting on light pollution, while still enjoying the energy-efficient benefits LEDs bring? Recommendations from the study suggest that we use less polluting, warmer LEDs with no blue emissions. Legislation to ban outdoor emissions of light at wavelengths shorter than 540nm will also go a long way in reducing the level of light pollution by street lighting, in addition to other practices such as shielding and eliminating over-lighting. So, know your LEDs folks!

Source: Fabio Falchi et al. (2011) ‘Limiting the impact of light pollution on human health, environment and stellar visibility’, Journal of Environmental Management 92, p.2714-2722