Tag: Kelvin

What We Know and Don’t Know About Color Temperature

The color temperature of outdoor lighting has become a big deal in the past few years. LED technology has given us incredible energy efficiency. But more and more we are learning that this benefit comes at a cost: Too much glare, too bright, to much harmful blue wavelength emissions, and more. The old technology these LEDs are replacing, low- and high-pressure sodium lights, don’t have any of those problems.

The current outdoor lighting ordinance in Ivins sets a maximum color temperature of 4,000 degrees kelvin. Our ordinance is very dark sky friendly, and at the time it was implemented in 2007 it was probably a model of dark sky friendliness.

But time moves on. The “gold standard” today is to install lighting with a color temperature no more than 3,000 degrees kelvin. That is the requirement for designation as a Dark Sky Community by the International Dark Sky Association (IDA).

But some argue that 3,000k is still too high. For more information, see articles by Christian Luginbuhl, a retired scientist from the United States Naval Observatory in Flagstaff at the Flagstaff Dark Skies Coalition.

So, last night we went out to measure the color temperature of some outdoor lighting in Ivins. We were accompanied by Rob Roush of Red Earth Development. He is developing the Red Desert subdivision in Ivins next to the Reserve. He contacted us last month because he wants to maximize the dark sky friendliness of his project and has been searching for answers about appropriate color temperatures for his development’s outdoor lighting.

Technological improvements are great, but they can create more work, especially for those who pay attention. Color temperature is something nobody ever had to pay much attention to.

First, a disclaimer. Our outing last night is just a preliminary step. We need to do a lot more research, especially since the results we got raised some questions. But it was eye-opening.

We used a high-end spectrometer, the AsenseTek Lighting Passport. It’s an expensive little device that costs about $2,000. It communicates with an app on your cellphone. We were fortunate to be able to borrow it from IDA.

We measured some of the bollards on the west side of Rocky Vista University on 200 N. The spectrometer reading as under 1,600k for these. We’ll have to doublecheck with the City, but we believe the light source is an LED rated at well over 2000k.

City staff told us they added a “lens” to these lights that seems to lower the color temperature. But that’s still a big difference. It may be caused by the light source bouncing off a bowl shaped dome, and the dome’s color lowering the color temperature. Well, there’s some homework.

The color temperature of one of the city’s cobra lights was 1,851k. The light source in cobras is typically high pressure sodium. But they are slowly being replaced by LEDs.

We measured a number of other lights and got similarly low color temperature readings. Maybe the app we downloaded didn’t like our android phone. So Rob downloaded the app on his iPhone. He got the same readings.

For example, the newer post top lantern lights the City is installing were around 1,800k using both phones. We were expecting higher readings.

Maybe the AsenseTek spectrometer was giving us incorrect readings. That seemed unlikely. It’s an expensive, professional device.

But we were still concerned. Maybe we were measuring incorrectly. We tested that by taking a meter reading right next to the light source and a reading a number of feet away from the light source. We got the same result. That’s how it should be. We are measuring the color temperature of the light, not the amount of light, or illumination.

So we continued. The Veterans Center has parking lot lights that read just over 1,700k. These appear to be sodium lights. And it looks like a few were fluorescent, which came in at close to 3,000k. These readings made sense.

Similarly, the parking lot lights at Rocky Vista University registered around 4,000k. That also made sense. These are LED lights and our current ordinance allows lighting up to 4,000k. We found other parking lot lighting that had even higher kelvin readings, some close to 5,000k and some even higher. These were probably installations that predated our current ordinance.

Why go to all this effort? If we are going to recommend changes to the city’s outdoor lighting ordinance, we need to understand what lighting in the city might look like in the future.

This was a first step, and it certainly wasn’t a giant leap for Ivinkind, but at least it’s a start. We have some homework to do with IDA, AsenseTek, and the City.

If you have any expertise in lighting issues, we would value your input. Let us know if you are willing to help by emailing us from the Contact us page.

Shedding Light on Outdoor LED Choices

New technologies come with unanticipated challenges. With outdoor LED lighting, that turns out to be significant levels of blue light. As a result, most current outdoor LED lighting is far more damaging to us and our nighttime environment than the old technologies they replace. This article appears to be a bit technical, but please continue reading. It will all make sense.

Download a PDF of this article (336kb)

Feeling blue

The coordinated color temperature (CCT) of a light is an expression of its overall color. Higher temperatures correspond to bluer light. LEDs with CCTs of 4000K and higher, typical of today’s LEDs used for outdoor street and parking lot lights, emit a lot of blue light. That results in the bright, glaring white light we see all too often today.

Even LEDs with a CCT of 3,000K emit more blue light than the fixtures they replace. The three charts above show a clear trend. LEDs with lower CCTS emit less blue light.

Limiting blue

“Cold” blue light brightens the sky more than “warm” yellow light because blue light scatters more than yellow. That’s why the sky is blue. The blue component of white sunlight is scattered when it hits our atmosphere while sunlight of other colors comes comparatively straight through. So even when properly shielded, blue light contributes proportionately more light pollution than the same amount of yellow light. One goal of proper lighting is to reduce the amount of blue light in favor of more yellow.

Most LEDs emit blue light, but the amount varies based on the LEDs color temperature. LEDs with a CCT of 3000K or less typically emit about 25% of their light as blue and are preferred, so one goal is to use lights with a CCT of 3000K or less. When it comes to blue, less is better.

It’s all in the eyes

But it’s not that simple. Our eyes are much more sensitive to “cold” blue light than “warmer” yellow colors. That’s one of the reasons we react negatively to so much of the outdoor LED lighting common today, those lights are rich in blue light, much too rich.

“Warmer” LEDs are less efficient

LEDs are a lot more energy efficient than older technologies they are replacing. But warmer LEDs are less efficient than colder LEDs because they emit less blue light. A 2200K LED is only about two-thirds as efficient as a 3000K LED, meaning it will consume more watts to create the same amount of useful light.

Do the least harm

Although cold blue LEDS are more energy efficient than warm yellow LEDs, cold LEDs cause harm in a variety of ways that need to be taken into consideration. There are important justifications for preferring yellow LEDs to blue despite the cost differential. These are glare, medical problems, and aesthetics:

Glare

Blue LEDs are brighter, watt for watt, than yellow LEDs, but blue LEDs increase glare and compromise human vision, especially in the aging eye. Blue lights create potential road safety problems for motorists and pedestrians alike. Using innovative fixtures that employ frosted lenses or reflectors helps reduce glare, but at the cost of some efficiency, and that reduces the operating cost differences between warmer and colder LEDs.

Medical problems keep piling up

A 2016 American Medical Association concluded that “white LED street lighting patterns [may] contribute to the risk of chronic disease in the populations of cities in which they have been installed.” The AMA recommends “minimizing and controlling blue-rich environmental lighting by using the lowest emission of blue light possible” to reduce potential negative effects on human health.

And, although there is less light output per watt of electricity in the lower Kelvin temperature rated lights, the AMA considers that a good thing, as they affirm outdoor public lighting is not just too blue, it is too bright.

A Harvard medical study states that “…blue light has been identified for years as the most dangerous light for the retina.  After chronic exposure, one can expect to see long range growth in the number of macular degenerations, glaucoma’s, and retinal degenerative diseases.” 

A paper published by the American Macular Degeneration Foundation (AMDF) reports, “the blue rays of the spectrum seem to accelerate age-related macular degeneration (AMD) more than any other rays in the spectrum”.

Blue light also disrupts the circadian rhythms of humans, animals, and plants; and it has even been implicated in the global obesity epidemic. Light pollution may be making us fat. Blue light also disrupts nocturnal animal behavior; both wild and domesticated animals.

Aesthetics

It is not true that people automatically prefer the whitest and brightest light in all applications. Many people prefer low CCT outdoor lighting, especially in residential areas. The city of Davis, CA, for example, was obliged to replace newly-installed 4800K street lighting with 2700K fixtures at a cost of $350,000 following residents’ complaints about “prison-white” lighting.

What should we do right now?

  1. Limit outdoor LEDs to CCTs to no greater than 2700K, and preferably no greater than 2200K.
  2. Reduce both the number and brightness of outdoor lights to the minimum to provide safe and effective lighting.
  3. Use fully-shielded lighting.
  4. Use timers, motion sensors, adaptive controls, and curfews to limit lighting to when it is needed.

Special thanks: While we take full responsibility for the statements in this article, we appreciate the detailed review, corrections, and editing provided by John Mosley and information from Christian Luginbuhl, U.S. Naval Observatory, Flagstaff (Retired), and founder of the Flagstaff Dark Skies Coalition.