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.
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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?
- Limit outdoor LEDs to CCTs to no greater than 2700K,
and preferably no greater than 2200K.
- Reduce both the number and brightness of outdoor
lights to the minimum to provide safe and effective lighting.
- Use fully-shielded lighting.
- 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.