The American Medical Association (AMA) has unanimously adopted a policy statement concerning street lighting at its annual meeting in Chicago on June 14. The recommendation is to “cool it and dim it” in response to the widespread adoption of new LED street lighting across the country. An AMA committee has provided guidelines for communities to select LED streetlights that “minimize potential harmful human health and environmental effects.” Municipalities are replacing older streetlights with energy-efficient and durable LEDs to save on energy and maintenance costs. While the streetlights offer these benefits, the AMA underscores the importance of thoughtful design of new technologies and the close link between light and human health. The AMA advises that outdoor lighting at night, especially street lighting, should have a color temperature not exceeding 3000 Kelvin (K). Color temperature (CT) measures the spectral content of light emitted by a source, indicating the amount of blue, green, yellow, and red it contains. A higher CT rating typically signifies more blue content, making the light appear whiter.
White LEDs with a CT of 4000K or 5000K contain significant short-wavelength blue light and have been chosen by cities like Seattle and New York for their street lighting upgrades. However, these installations have led to complaints about the harshness of the lights. In Davis, California, residents even demanded a full replacement of these high color temperature LED streetlights. Is it possible for communities to have more efficient lighting without compromising health and safety? Traditional incandescent bulbs have a color temperature of 2400K, meaning they have much less blue and more yellow and red wavelengths. Before electric lighting, sources like wood fires and candles, which have a CT of around 1800K, were used, resulting in quite yellow/red light with minimal blue. Modern “white” LED street lighting, rapidly being installed across various cities, presents two issues according to the AMA. The first is discomfort and glare. Due to the concentrated nature of LED light and its high blue content, it can cause significant glare, leading to pupillary constriction. Blue light scatters more within the human eye compared to the longer wavelengths of yellow and red, and sufficient levels can damage the retina, affecting clear vision for safe driving or walking at night. This discomfort is evident when looking directly at the control lights on modern appliances, which can be painful. Street lighting with high blue content and inadequate shielding can have a similar effect.
The second concern addressed by the AMA is the effect on human circadian rhythms. While color temperature predicts the spectral content of light, it is primarily designed for light from incandescent bulbs with tungsten filaments. However, CT does not accurately measure light from fluorescent and LED sources. Instead, correlated color temperature (CCT) is used, adjusting the light source’s spectral content to match human vision sensitivity. Even with a CCT of 3000K, two light sources can have significant variations in blue light content. Therefore, the AMA’s CCT recommendation of below 3000K might not be enough to ensure minimal blue light. The actual spectral irradiance of the LED, indicating the relative amounts of each color produced, should also be considered. The AMA policy statement’s timing is significant as the new World Atlas of Artificial Night Sky Brightness has just been released, highlighting street lighting as a major contributor to light pollution.
According to the AMA, one key consideration when lighting the night is its impact on human health. Previous articles in The Conversation detailed how lighting affects our circadian physiology, its potential to cause serious health issues, and its effects on sleep. White LED light is estimated to be five times more effective at suppressing melatonin at night compared to the long-used high-pressure sodium lamps with equivalent light output. Melatonin suppression signifies circadian disruption, including sleep disturbances. Bright electric lighting can also negatively impact wildlife, disrupting migratory patterns of birds and certain shore-nesting aquatic animals. The AMA’s new policy statement includes three recommendations: First, they advocate for a “proper conversion to community-based Light Emitting Diode (LED) lighting,” which reduces energy consumption and fossil fuel use. Second, the AMA encourages minimizing and controlling blue-rich environmental lighting by using lighting with the lowest possible blue light emissions to reduce glare. Third, the AMA recommends the use of 3000K or lower lighting for outdoor installations like roadways, ensuring all LED lighting is properly shielded to minimize glare and harmful human and environmental impacts. It suggests utilizing the ability of LED lighting to be dimmed during off-peak times.