LED (Light Emitting Diode) lights
LED lights are 50% more energy efficient and last 2-4 times longer than conventional street lights (i.e. high pressure sodium lights). This creates a financial incentive for people, governments and businesses to move towards replacing incandescent or high pressure sodium lights with LEDs. An indirect benefit to health is associated with the reduced carbon emissions of LED lighting relative to current lighting.
How do LED lights work?
LED lights emit large amounts of blue light, which passes through a yellow phosphor coating to create the white light that we see. Despite the white appearance, LED lights emit a strong peak at blue wavelengths. In contrast, high pressure sodium light bulbs emit warmer colours from the red spectrum.
What are some potential health effects of LED lights?
Human eyes are more sensitive to blue lights because they scatter more within the eye and cause glare effects, which has implications for road safety. High intensity blue light also affects the retina and alters the circadian rhythm (i.e. sleep patterns) with the potential to contribute to chronic diseases. The likelihood of adverse effects depends on several factors such as length and frequency of exposure. For example, truck drivers who drive long distances at night for a prolonged period are more likely to experience circadian rhythm disruptions than a person who only occasionally drives at night.
Colour emitted by any light source is often expressed as a measure of temperature in Kelvin (K). Discomfort experienced by citizens from 4000K unshielded LED lights in Davis, CA and Seattle, WA has been reported in the media. Some described the lighting as having a "prison atmosphere" and some reported that they needed to buy thicker curtains to block the street lights. These effects can be minimized by proper shielding and using 3000K or lower colour temperature for LED lights. Increased light pollution from the use of LED lights can also negatively impact the environment, depending on characteristics of the light such as colour and degree of shielding. For example, it has been reported that excessive lighting can interfere with the ability of birds and turtle hatchlings to use moonlight to navigate.
Can the health effects of LED lights be reduced?
The negative health and environmental effects of LED lighting can be reduced by proper design, engineering and use. Some characteristics of LED lights that can be manipulated are colour temperature, amount of shielding, and brightness.
- Correlated Colour Temperature: Light sources with higher temperatures (or higher Kelvin value) emit more blue light than light sources with lower temperatures, which emit more red light. Current street lights, usually high pressure sodium lights, are 2100K (considered low Kelvin value) and emit light that is in the red spectrum. First generation LED lights are 4000K and emit high amounts of blue light. Recently LED lights have been created with colour temperature of 3000K or lower. 3000K LED lights emit slightly less (9%) blue light and are 3% less energy-efficient than 4000K lights. The American Medical Association (AMA) recommends the use of 3000K or lower LED lights for streets.
Figure 1: Relationship between colour emitted and temperature in Kelvin scale. Modified from International Dark-Sky Association
- Shielding: Shielding (Figure 2) is a technique that allows the light to be directed and maintained at ground level. Looking directly at the glare from an unshielded LED light, which is a bright point source, can cause significant fatigue and glare. Further, unshielded lights send much of their light away from the ground, and contribute to light pollution. The AMA recommends shielding be designed to ensure that no light shines above 80⁰ degrees from the horizontal (Figure 2).
Figure 2: Effects of shielding on light transmission. Modified from Goldendale Observatory
- Brightness (Lumen output): When replacing light fixtures, an important consideration would be to ensure the new LED fixture is not brighter than necessary for the intended purpose. If available, guidelines or standards addressing acceptable levels of brightness should be consulted.
- Adaptive controls: Dimmers, timers and motion sensors can be used to trigger lights to come on only when they are needed (for example, between evening and morning twilight, when traffic is approaching, or when motion is detected at night in a parking lot). The AMA recommends that road lights be dimmed off during off-peak periods.
Human and environmental effects of light emitting diode (LED) community lighting, American Medical Association