Nighttime Outdoor Lighting and the Challenge of Light Pollution
For millenia humankind has been awed by the night sky, with the moon, millions of stars, inky darkness, and the winding ribbon of the milky way. But since the advent of electrical lighting, the view has begun to change as streetlights, neon signs, stadiums, transportion networks, illuminated billboards, and a vast array of commercial, industrial, and residential building lights now shine through the night.
On an overcast night when the cloud layer reflects the artificial lights below, the night skies over our cities can be hundreds or even thousands of times brighter then they were 200 years ago.1 In fact, 80% of the world’s population (and 99% of the United States and Europe)2 now live under “sky glow”—a halo that is the cumulative effect of all artificial illumination in our cities, towns, and suburbs. To see the pattern of light pollution in your area or around the globe, view this interactive Light Pollution Map.
The Milky Way galaxy and stars—a view many of earth’s populations will never see due to living in urban environments where sky glow is pervasive.
Astronomers and scientists have been warning of the negative effect and potential harm of all this artificial light on humans by disrupting our circadian rhythms (learn more in this post on Human-Centric Lighting). Nighttime lighting doesn’t only affect humans, however, but can harm animal species and ecological systems too. For example, it can:
- Disrupt behavior patterns of nocturnal species who depend on darkness to stay safe from predators.
- Alter reproductive of species such as frogs that are critical to the health and balance of wetlands
- Threaten the survival of disoriented baby sea turtle hatchlings. Every year in Florida alone, lights along beaches lure millions of newborn turtles inland to their death instead of out to sea.
- Kill many birds who are confused by the lighting on tall buildings and towers. Lights also disrupting normal seasonal migration patterns.
Glowing night skies above the city of Bangkok.
Another nighttime light concern is the proliferation of bright objects in the sky that are neither stars nor planets: satellites. More than 4,500 satellites3 are currently in orbit around the Earth, posing a challenge for astronomers. Satellites can leave bright streaks in telescope images, interfering with analysis of both near and deep-space phenomena.
Outdoor Lighting Needs & Requirements
Municipalities and outdoor venues are now challenged with balancing these light concerns with the needs of creating an effective nighttime illumination scheme for their communities. Considerations include brightness, color, and energy efficiency.
An essential consideration is brightness. Most outdoor lighting applications require high-brightness (high lumen) lighting fixtures that can dispel darkness at night. Illuminating urban streets, parking lots, roads, and the nation’s highways is a critical element of modern life, ensuring safety for vehicles, pedestrians, cyclists, and everyone on the road. These lights need to be bright enough for clear visibility of objects and people.
When designing street lighting, the first taks is to meet the regulatory requirements of the federal, state, or municipal area. For example, the US Department of Transportation Federal Highway Administration has published standards for Roadway Lighting to ensure nighttime visibility on the nation's roads.
But as light pollution has become a concern, lighting manufacturers and designers have had to start adjusting their approaches. One way to mitigate light pollution is to install more focused, directional lighting fixtures. Directing light downwards and minimizing any side or upwards beams can help reduce unnecessary glare. Mechanisms such as motion sensors that turn on lights only when activity is detected can also reduce unnecessary brightness and lower energy use around our homes and buildings.
In addition to brightness, color temperature (CCT) is also an important consideration for street lighting (refer to the image below). "The American Medical Association has recommended that nighttime street lighting should have a color temperature no higher than 3000 Kelvin (K) to avoid too much blue light, which can interfere with human and animal circadian cycles.
Color rendering also matters, as artificial lighting can be the only source of illumination in an area at night. Poor color rendering can alter the appearance of objects in the environment, impairing visibility."4 For example, poor color rendering can make a read object appear black.
Replacing HPS streetlights (left), which have poor color rendering and higher energy costs, with LEDs (right) has a significant impact. For example, LED implementation has resulted in 64% energy savings for the City of Los Angeles, while still meeting the LABSL standard of 3000 K and > 70 CRI for LED installations. (Photo credit)
An additional characteristic of newer outdoor illumination installations today is their energy efficiency. Growing concern over the greenhouse gas emissions from legacy electricity generation plants, combined with the rising costs of electrical power, has created more urgency in the demand for energy efficient lighting. Essentially, the goal is to achieve the same high brightness with much less power input than traditional outdoor lights such as incandescent, sodium, compact fluorescent, metal halide, etc.
For example, a sports stadium lit with LED fixtures can save as much as 75% of electrical costs5 over metal halide lights. These savings can quickly add up to tens of thousands of dollars per month for a large collegiate or professional stadium. While LED light fixtures can cost more for initial installation, the longer lifetime of LEDs (up to 30,000 hours or more when operated at 70% of maximum brightness6) easily makes up the difference.
Adapting to Reduce Light Pollution: LEDs Provide a Solution
For exterior applications, LEDs have an optical design advantage because they emit focused, directional light without excess illumination diffused in all directions, and can provide brighter light (higher luminance) on target at the appropriate CCT, using less energy than previous technologies. LEDs perform well in outdoor lighting schemes when judged based on original price and power consumption, key attributes of the cost of ownership. LED streetlights have been found to reduce energy use by 40-60%.7
Mitigating light pollution can start with improving streetlamp design. (Image Source)
LED Performance Testing
These are just a few examples of innovative LED applications. Before LEDs and lighting products reach the market, however, significant research, development, and testing goes on behind the scenes. Manufacturers of LEDs and luminaires must ensure that products not only provide the brightness (luminance) and color (chromaticity) performance that users expect, but that LED products also comply with industry safety regulations and standards such as:
- Underwriters Laboratory, such as UL 8750
- CE and RoHS certification in the European Union.
- Illumination Engineering Society, such as ANSI/IES LM-79-19
- And other similar organizations and certification standards around the globe.
Obtaining Measurement Data for LEDs and Light Sources
For 30 years, Radiant has provided solutions for measuring luminance, chromaticity, and other characteristics of light sources. One of the company’s very first products was a goniometric measurement system to capture light source data from multiple angles. Now in its fourth generation, Radiant’s SIG-400 (Source Imaging Goniometer®) is a fully automated, computer-controlled goniometric system designed to meet the needs of LED researchers, developers, manufacturers, and users by providing LED die and device characterization.
The SIG-400 precisely measures near-field luminous intensity for LEDs and other small light sources. It captures and aggregates images and flux measurements from thousands of angular viewpoints around a light source to precisely characterize the source's near-field output in three dimensions. The SIG-400 also supports measurement of vertically oriented light sources and can be used with both microscope and extended-field-of-view optics, thus providing the flexibility to measure both LEDs and other light sources.
Radiant's SIG-400 (left) and an example of SIG-400 system imaging results of a light source, shown in false-color scale (right).
- “Light Pollution Effects on Wildlife and Ecosystems.” International Dark Sky Association. (Accessed September 16, 2022)
- “Light Pollution.” National Geographic Resource Library. (Accessed September 15, 2022)
- Whitt, K., “Who Owns All the Satellites?” EarthSky, February 8, 2022.
- Lighting for Health: Human Centric Lighting. Luminus Devices, August, 2021.
- "LED Lighting." U.S. Department of Energy. (Accessed September 19, 2022)
- Itrogers_dev, “Use LED Lights to Reduce Light Pollution.” LED Light & Power, February 15, 2017.
- "Lifetime of White LEDs." Pacific Northwest National Laboratory, PNNL-SA-50957. September 2009