> Moonlight is around 4100K. So it is even more "natural" than 3000K. Should we blot out the moon next?

I was on a hike in July during a full moon and those who were sleeping in open air (no tent or bivy bag) struggled to sleep through the night due to the moonlight.

This was in the North West of Australia, so daytime maximums were around 35C. It was too warm at night to zip your tent or bivy closed, so where possible you would try to position yourself so that you could shield yourself from the moonlight during the night.

There were quite a few afternoon nappers in the group until the moon waned a little by the second week.

Perhaps this is our bodies telling us something, a piece of our evolution. Perhaps we aren't meant to sleep in the open. We are easy prey at night. Sleeping in moonlight, out in the open, is dangerous for prey animals. A dislike for sleeping in moonlight might therefore be a survival tool. Those uncomfortable with moonlight were more likely to be sleeping under cover and less likely to be hauled off by lions.

Even worse is the extreme latitudes in summer! I tried sleeping under just a mosquito net in Alaska when the sun stayed up until 2am and rose again by 4. I brought a sleeping mask but found it hard to keep on, as we'd encountered three separate grizzlies earlier that day…

At lower latitudes, a full moon over snow is stunning and surreal when you can get away from local light sources - no flashlight required. Light at night (of appropriate color temp) is quite natural.

I sleep in a hammock on my balcony quite a bit and without covering your eyes it can be a real struggle when the moon is near full and the skies are clear. One thing mentioned elsewhere is the idea that darkness = safety. I can imagine that to be very true for humans.

No one carried a bandanna that they could use as an eye mask? I've done that even when the night time low was 35C.

In situations like that I use any random piece of clothes as an eye mask, so yeah, I don't see a problem either.

>Should we blot out the moon next?

Why not? Lets fund an orbiter to create an artificial lunar eclipse exactly on full moon.

I would also submit that Kelvin is not an appropriate reference for the colour of LED lights. Kelvin only makes sense when discussing blackbody emissions, it is essentially a description of temperature. LEDs do not create light via simple heating. Their spectrum is not the smooth blackbody curve that the kelvin scale suggests. It is in fact a combination of several strong emissions at narrow wavelengths that combine to fool our senses into perceiving white light.

Proper discussion of harmful emissions from LEDs should instead speak of intensities at a particular wavelength and perhaps ratios between wavelengths rather than an outdated reference designed for blackbodies.

While I agree with you from a standpoint of accuracy, Kelvin is still really useful. It also happens to map pretty nicely to how we perceive color.

The N-step MacAdam ellipse on a 2D CCx/CCy plane is what gets used when you dig into tint, but people love to reduce complex systems to a single number. And if you want a single number, temperature is the best we have.

I'm curious what your suggestion might look like in practice because it would be even more complex than the MacAdam ellipse.

In practice, I could see a simple description of the intensity of visible along with a percentage of the 'bad' light within that intensity. That is an analog for how our eyes actually function. We have a retina that sees specific wavelengths, but an iris that regulates the amount of light hitting the retina based on an average intensity across the visible spectrum.

Harm comes to our eyes when 'unnatural' non-blackbody light plays tricks with the system. Looking at an eclipse isn't harmful because of some new light that only exists during an eclipse. It's because the darkness allows our iris to open despite the presence of harmful UV light. (The same goes for vintage sunglasses that don't block UV.) So to discuss the biological safety of light one needs, at a minimum, both the average intensity to judge how open the iris will be, and some reference for how much harmful light is present. Imho that can be expressed as an intensity and a percentage. An eclipse is a low visible intensity with a high percentage of harmful light. These blue-heavy LEDs could be similarly described.

CRI accounts for this, though it does not reveal the specific wavelength components. You can however be confident a 90+ CRI light source is not going to have an unexpectedly high intensity of any given wavelength.

What matters isn't color temperature, but the presence or absence of light in the range 360-405 nanometers, which activates certain neurons in the retina that suppress melatonin secretion. This light can be "unseen" because visual receptors don't respond particularly strongly to it, so it can be masked by much stronger emissions of yellow light. However, it still has an effect. Color perception is irrelevant in this case.

http://press.endocrine.org/doi/abs/10.1210/endo-119-5-2201?j...

http://jap.physiology.org/content/110/3/619.short

Fires and the moon emit very little light at this frequency.

405nm is violet. 360nm is UV. Yes, we are sensitive to it. But white LEDs emit none* of either.

*Future generation of LEDs might shift from indigo (445nm) to violet to improve color rendition, but cost will go way up and efficiency will go way down so I doubt it will be common. And some stores are already adding UV LEDs to their lighting in order to make florescents really pop.

Edit: and a reference, the datasheet for the latest and greatest XHP50 LED: http://www.cree.com/~/media/Files/Cree/LED-Components-and-Mo...

Spectral charts are on page 11. Peak emission is at 445nm. Beyond 415nm there is nothing.

Cheaper LEDs will use a longer wavelength of blue, typically around 475nm.

My city used old-style mercury-vapor street lights up until the early 80s. For those who have never seen these lights, they have a bluish-white appearance but emit light only at a few very specific wavelengths, and almost none in the red spectrum. The effect is that under these lights a red car would look strangely black while everything else more or less looked normal color. I loved the effect.

I have fond childhood memories of seeing my street bathed in the bluish-white light from these street lights, especially during those long winter nights when the ground is covered in white snow. I am quite certain that these street lights did not produce a generation of "physiologically unwell" people.

My city has now begun switching to LED lights and I think they look terrific.

These mercury-vapor lamps were used until 90-somethings where i used to live. People would say that until these bluish-white lamps were phased out by orange ones, people in the street would look as if they were dead; I would always counter with "they sure look as if they're alive now". Maybe because of childhood nostalgia I always preferred the bluish-white nights instead of that pervasive orange ones, especially during overcast winter nights where everything in thirty kilometer radius would become orange and unnatural. Clear nights with full moon were godsend.

But things are changing nowadays and our city also started using LEDs and by Moses, they are so much unbelievably better in all aspects! Even if they emit that "unseen blue" light, it is most definitely not worse than the insanely pervasive orange...

I think the author is inferring the https://en.wikipedia.org/wiki/Kruithof_curve. We apparently prefer dimmer light sources to be warmer.

This is an obnoxiously dismissive comment build on ignorance and shoddy reasoning and an “I don’t care what you think just suck it up and stop complaining” approach to design/policy.

The moon is one (1) singular source of light with a known peak intensity, often blocked by trees or clouds, and only at its brightest one day every month. On a full moon night, the moon is high overhead, not directly in your field of view if you’re looking straight ahead.

LED streetlamps are a dozen or more point light sources, directly in the field of view, each one of them individually brighter than the moon. The 4000K LED streetlamps installed on my street last year have a very sharp spike in the short wavelength part of their spectral power distribution (come to my street and I’ll lend you some diffraction grating glasses to see the spectrum for yourself). The LED lamps are also incredibly bright, I’d say 2–4x the luminance of the prior streetlamps or the sodium lamps on nearby streets.

Because the new lamps are brighter, cities save money by using fewer of them, spaced more widely. This causes the light to be less even than past streetlamps, meaning some parts of the street are intensely illuminated and other parts are in shadows. The lamps are shielded at the top, but they shine out to the side at a very wide angle, meaning they still cause a ton of glare from a block away or more. When originally installed they had poor shielding in the direction of people’s second-floor bedroom windows. They’ve since fixed that problem and only people on the first floor still have light shining directly into their windows.

Seeing these and objects they illuminate in your peripheral vision causes the eyes to become bright-adapted (i.e. entirely knocks out night vision) making objects in shadow appear darker than under other lighting, and the whole scene to have very high contrast. (It takes something like a half hour to become dark-adapted once again.) The glare is extremely distracting. Overall they make the street feel like an industrial warehouse.

The light is not like fire, or past streetlamps.

Beyond that, the new lamps are not more energy efficient than modern sodium lamps. Indeed, if you make them more than twice as bright, they use substantially more energy than well made sodium lamps.

When I walk my dog at night I’ve taken to wearing orange safety glasses (basically plastic filters which block out the short-wavelength part of the spectrum). That I can see noticeably better after blocking half the light put out by these streetlamps indicates that there is some problem with their current design. (With the orange glasses, my rod vision continues to function properly.)

LED streetlamps should be at ~2700K CCT or below, with almost no light in the blue part of the spectrum. They should be no brighter than past streetlamps. They should be placed close together and not too high up, and shielded to mostly direct their light downward rather than sideways.

Under such circumstances they would be fine. (LEDs aren’t an inherently bad technology. They have the advantage that they last longer without needing to be replaced. This saves money for city maintenance departments.) Unfortunately current models on the market don’t meet those criteria.

Same story for car headlamps. The current LED headlamps are a safety risk (blinding pedestrians and other drivers with the glare). LED technology could be used to make fine car headlamps; it’s the ones currently on the market that are terrible.

Well ... the article is poorly written; clearly the author doesn't understand the science.

But you make some good points. I support your recommendations.

Yes, I was a little glib. But nonetheless life on Earth (not just our species) evolved with a 4100K light source at night.

You are confusing color temperature with how the lights are installed. If your streetlights were 4000K and spaced properly you wouldn't have an issue with them. The penny-pinching distribution (high lumens, wide angle, distantly spaced) of lights chosen by your city is at fault. That layout will create maximum glare and is the most miserable layout imaginable since distant lights will always be shining directly in your eyes.

> You are confusing ...

I have spent 10 years studying color science. I know what color temperature is. I’m just explaining why the moon is a poor analogy. I have an issue with bright short-wavelength light sources at night, regardless of lamp configuration. It knocks out night vision.

There is a wide literature (dozens if not hundreds of research papers) on this topic. It’s not exactly some deep mystery.

The lamp configuration just makes things worse (and the use of fewer, brighter lamps provides much of the economic incentive to install the new lamps, along with federal subsidies).

Do you mean that there are places where street lights with other technologies are replaced with LEDs by leaving every other lamp post empty?

That is a problem that LEDs could enable (by making very bright lamps available) but is not really a problem of LEDs but a problem of using any bright light source wrongly.

My understanding is that the use of lower-energy and more durable light sources provide most of the incentive to install new lamps. I.e. electricity bill is lower and you need to change the lamps less frequently which reduces maintenance cost.

They rip the poles out, and replace them with fewer new poles (taller, wider spaced, with brighter lamps).

This makes the installation cost more attractive to the city.

The electricity bill is (potentially) lower if you replace very old lamps with LEDs at the same brightness.

The best sodium lamps are quite efficient though, so LEDs have only marginal advantage compared to replacing the old lamps with newer sodium lamps. If you make the LEDs dramatically brighter, then they actually end up using more electricity.

I haven’t seen any especially convincing numbers about an LED lamp project that saved on electricity bills. I’m not an expert in the subject though, and I haven’t looked too deeply into digging up data.

> ... evolved with a 4100K light source at night

As others have noted, we sleep poorly under strong moonlight.

I live in a very rural wooded area, and I can leave my blinds open except when the moon is at its brightest -- I sleep very poorly if I don't use blackout curtains.

Perhaps the fittest humans were the ones who stayed the most awake and aware of nocturnal predators during the brightest nights of the month?

Noticed in my parents' town with their recent deployment. The LED lights appear to be more tunable and/or actually tuned, to put light on the street while keeping it off of houses.

So, "blue" whatever. If you are keeping my yard dark so I don't have to pull the shades just to block out the light, well, win!

Of course, other areas that still feel the need to light up every square centimeter because security, YMMV.

I'll add that I find the current LED streetlight colors better than the orange sodium vapor "malaise" that we've grown so accustomed to.