When the Lights Go Down in the City

The American Medical Association (AMA) issued a policy statement at their annual meeting in Chicago on June 14 regarding street lighting. Many cities are replacing their high pressure sodium lamps with long-lasting LEDs to save money on energy and maintenance. The AMA issued guidelines of how to choose LEDs that minimize harmful human health and environmental effects. There is a close connection between light and human health.

The guidelines recommend outdoor lighting, including street lights, have a color temperature (CT) of no greater than 3000 Kelvin (K). CT is a measure of spectral content: how much blue, green, yellow, and red is in it. Higher ratings means there is more blue and the whiter the light appears. The standard LED installed in a number of cities has ranged 4000K to 5000K, and many have complained about the harshness of the light. In comparison, an incandescent bulb has a CT of 2400K and candlelight is about 1800K.

The new “white” LED lights cause discomfort and increase glare, resulting in constriction of the pupils in the eye. Blue light scatters more light in the eye than yellow or red, and sufficient levels can damage the retina. This causes problems seeing clearly for safe driving or walking at night.

The lights also affect the human circadian rhythm. White LED light is five times stronger at suppressing melatonin at night than the old streetlights. Suppressing melatonin disrupts sleep. Bright lights can also affect wildlife, disturbing migratory bird patterns and aquatic animals which nest on shore.

The CT rating does not measure color from fluorescent and LED lights well, so another system called correlated color temperature adjusts the spectral content using sensitivity to human vision.  Therefore, two 3000K light sources can have large differences in blue light content.

Street lighting is a large component of light pollution. The AMA encourages minimizing the use of blue lighting to reduce glare by properly shielding the lights and dimming them during off-peak times.
Stevens, Richard G. “Bugs”. “Doctors issue warning about LED streetlights.” Health. CNN, 21 Jun 2016. Web. 23 Jun 2016.

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