Warm White LED Streetlights: Why They're Better for Our ...

CCT will tell you what hue and tone of white to expect from a specific streetlight. It is measured in Kelvin (K), which is similar to degrees in Celsius. Different temperatures on the Kelvin scale represent different colors. For example, light at 2000K-3500K looks more orange/yellow and is called ultra warm or warm white, and as temperature increases in Kelvin, color changes to more of a “paper white” known as natural or neutral white (between 3500K and 5100K) and finally into a bluish-white known as cool white (5100K-20000K).

LED streetlights are great for the environment. They consume much less energy than standard high-intensity discharge ( HID ) lights, last three times longer, and they reduce greenhouse gas emissions and maintenance costs. In general, LED lights also contribute less to light trespass because they emit direct illumination. Because of all their great qualities, many cities have started to convert from HID to LED streetlights . What some cities have failed to consider, however, is that while LED streetlights are capable of emitting different colors of light, not every color should be used in public outdoor spaces. Bright blue-rich white light can cause some issues for residents, local wildlife, and night sky visibility. When it comes to streetlights, the warmer the color/correlated color temperature ( CCT ) the better.

The International Dark-Sky Association (IDA), a group whose purpose is to protect the night sky, recommends that LED street lights have a CCT of 3000K or less. These street lights will have a warm white glow that is safer for people and wildlife. The CCT of daylight is right around 6500K, which appears pretty blue. Introducing that type of light into people’s homes through their windows at night can suppress melatonin production and disrupt circadian rhythm. Melatonin doesn’t just help us fall asleep; it has antioxidant properties, boosts the immune system, and regulates certain hormones. There have been studies showing that it can even aid in IBS as well as migraine and cancer prevention.

Throughout the day, light changes from a warm white color at dawn to natural white then to a cool white in the afternoon, back to natural white, and eventually to an ultra warm white color at sunset. Our bodies are used to this cycle of light. Artificial lights that deviate from the natural lighting cycle can throw off our circadian rhythms. The National Institute of General Medical Sciences states that, “Circadian rhythms are physical, mental and behavioral changes that follow a roughly 24-hour cycle, responding primarily to light and darkness in an organism’s environment.”

According to healthybuildingscience.com “. . . different types of light trigger different physiological effects. Blue/white light, akin to a bright midday light, suppresses melatonin and increases serotonin, this light is great for activity. Conversely red/orange light triggers melatonin in preparation for going to sleep. If everything is in balance, the body will generate dopamine, serotonin, cortisol and melatonin in the right quantities at the right time of day.”

On their website, the IDA cites important information from a report about human and environmental effects of LED streetlights. According to this report, studies have shown that being exposed to light with a higher CCT before going to bed can negatively affect sleeping patterns. The report goes on to say that continuous sleep disruptions can lead to cancer, obesity, heart disease, and diabetes.

In addition to the possible effects on health, cool white street lights can increase disability glare. Disability glare happens when stray light enters the eye and affects your ability to see distances and space correctly. According to the report, this happens “. . . because blue light scatters more within the human eye.”  While it’s not directly causing harm to someone’s health, glare decreases driver safety and can lead to traffic accidents.               

At night, blue light used outdoors can also wreak havoc on ecology. Introducing light with a CCT that’s close to daylight essentially changes the daily cycle that plants and animals are used to. They depend on this cycle of light and dark for hunting, reproduction, sleeping, migrating, and protection. Nocturnal animals have suffered greatly from cool white light at night; the IDA reports that, according to research scientist Christopher Kyba, “. . . the introduction of artificial light probably represents the most drastic change human beings have made to their environment.” Insect populations are declining because they are attracted to the cool white light. They circle under it until the point of exhaustion and death. Plants, birds, and other animals need insects to survive, so this fact alone greatly affects our ecosystem.

Posted 01 September 2022 - 06:01 PM

Shielding is the most critical aspect to consider. However, almost all LED streetlights are fully shielded these days since it is more energy efficient, so I would be surprised if any of the options were not already full cut off. The only ones that might not be shielded are period-style or decorative fixtures, although shielded options are available for those too. 

The next most importance aspect is the intensity. While some may argue that brighter is safer, it's important to make sure your city understands that this is not always the case. Excessively bright lights cause blinding glare, and also force our eyes to adjust to the bright conditions, thus we are less able to see well in darker areas. The unfortunate side affect of this is that even more light becomes necessary for adequate vision in areas adjacent to a bright light, when if the light was dimmed the extra lighting would not be as necessary. 

You can determine the intensity with a cheap light meter from amazon or other retailers. They may not be perfect but good enough for a simple comparison. 

Third, the color matters. The more amber the color, or lower the correlated color temperature (Kelvin), generally speaking the less impact it will have on the night sky. Blue light (shorter wavelengths) scatters more in the atmosphere than red light (longer wavelengths), so blue contributes more to skyglow, and it is not linear. Blue scatters about 4x more than red. Blue light is what disrupts circadian rhythms, plants, and animals the most. So from an astronomy and environmental perspective, less blue or no blue at all is best. 3000K or below is what the IDA currently recommends, but they indicated that their recommendations will likely be even lower for streetlights soon. Near McDonald Observatory in Texas, some communities have opted for 2200K for their streetlights (astronomy and environmental concerns being the primary motivation). 

Some may claim that white / blue light is safer, but there isn't really much rigorous evidence for this, and what evidence exists is highly context dependent. Our eyes naturally adjust for the color cast of a scene. Bright blue lights can make driving in fog or rain especially difficult. But white/blue also provides greater contrast in good conditions, albeit at the cost of losing our ability to see in unlit areas, so there's debate over what is safer. It may be that the pros and cons of each pretty much cancel each other out. 

Lastly, consider adaptive controls. Many streetlights come with an option for adjustable brightness or timing. So for example if a resident complains about a light, the light could be dimmed to be less intrusive. Or lights could be turned off late at night when fewer people are active to help save energy. The energy savings of dimming / timing strategies often more than offset the cost of the controls over a few years. 

Here is a great video about a town retrofitting their streetlights with LEDs, done right: https://www.youtube....aye8Uog&t=1794s

Edited by SirHumHum, 01 September 2022 - 06:04 PM.