Thursday, April 27, 2017

Imperceptivism: Why ·IsN't· The Sky Blue?

(this is follow on 1 of at least 4 from the original Imperceptivism blog)

“Daddy, why is the sky blue?”

“Because, Darling, your eyes are limited.”

That’s not the answer your parents told you.  Yet it is factual.  Most kids are told the usual answers: The blue light is scattered by small atmosphere molecules, while the other colors come down from the sun directly. Or the trite, “to match your eyes, Darling.”


"Unseen filtering" of a sunset at the Orlando Eye (left) and Universal's park area (right)

Still the sky is not just blue, it’s many unseen colors.  Of course clouds can take on all sorts of color.  Twilight low atmosphere scattering can alter the sun’s path to give a dispersion of golden yellow, hot fuchsia, even eerie green.  However a hazeless, cloudless sky is just blue to the naked eye.  On a clear sunny day, if you look at a hard shadow (with sun adjusted eyes) it will at first look mostly bluish in color, until your eyes adjust to the shadow.  That blue color of the shadow is because the light reaching the sun-blocked area is from the rest of the sky—blue to our limited eyes—and why Shade White Balance is about 2000 degrees Kelvin bluer than summer sunshine (which itself is about 3000K bluer than the 2000K light of a sunset). What you won’t see is the near infrared, ultraviolet and more that do radiate from the sky into that shadow.
Full Spectrum UV-IR filtered photo.  Zoom in inset with increased saturation shows the shadow under the pavilion takes on a purple tone, which contains mostly UV/Blue radiance.

Our unaided eyes are severely limited in sensing properties of light—they cannot sense light phase, they cannot sense polarization*, they cannot sense ultraviolet or infrared.  Most photographers use polarizers to deepen the blue sky where it is polarized in a band across the sky-dome at 90-degrees from the sun’s current position, relative to our observation angle.  That’s technical talk for saying you use a filter to do what your human eye can’t—it has nearly no ability to see polarization without a pair of trendy sunglasses*.  But some insects, arthropods, cephalopods, octopi, amphibians and fish can and do sense polarized light (as well as a multitude of colors from UV to IR). Bees and dragon flies (among other creatures) use polarization to navigate.  More on that in another Next Eyes blog.

    [ *W. K. Haidinger found that the human eye can perceive a slight amount of polarization due to dichroism in a retinal pigment (i.e., Lutein) that contains light-sensitive long chain molecules oriented radial in the retina.]


Unseen filtering of a sunset behind Universal's Volcano Bay flanked by hotels

An interesting side note, already touched upon in the first post of this blog series, is that brown eyes block (reflect) more infrared light than blue eyes.  Some have speculated that mutations in the genes that code pigment holding retina proteins may allow eyes to have increased color range sensitivity.

The sky is filled with radiance that eyes, even insect eyes, cannot sense.  Spectral irradiance, caused by upper atmosphere airglow, is several times stronger at night in the 900 to 1700nm band than in the visible range at night. The sky in that band would appear almost as bright as a full moon when the moon is absent.

The atmosphere nightglow is as radiantly bright from 1.2-2.0um as a nearly full moon

The eye also cannot detect the x-rays, microwaves, radio-waves, thermal infrared emissions and neutrinos streaming down from space through our sky, day and night.

The title of this blog post uses the word Isn't on purpose in posing the question.  So why isn't the sky ultraviolet colored? Why isn’t the sky infrared colored? Why isn’t the sky thermal-emissions colored? Microwave colored? Or neutrino colored? Whatever that means. 

Unseen Filtering of a "Jackson Pollock" styled morning pre-sunrise sky

The father answered it at the beginning: The sky is blue because that is all you and I can perceive of all the different energies currently known radiating in our sky.  We have a very limited, narrow cone of perception.  Think about a long day of highway driving or computer monitor staring without much of a break. By the end of the day, your mind is still narrowly imagining the rushing road or the myopic window of that monitor. Your after-view is narrow.  In a sense our entire life is a narrow experiential tunnel due to being gravitationally tethered to a trillionth-trillionth percent of the universe (i.e., stuck on earth). Most of us don’t wander a few hundred or thousand miles out of our home land.

But you don’t need to wander past your own yard to experience the grandeur of light unseen and so beautiful it might alter your viewpoint.  Using filters to remove seen light and add light unseen, your own backyard sky will inspire.  You too can encounter and contribute art to the imperceptivism movement.

Many photographers know that a fluorescent-light-correcting filter, denoted as FL-D or FL-W, can provide increased saturation of the blue and red end of the spectrum during sunsets or sunrises.  (I personally use the Hoya HMC FL-W.)  These optical filters remove a portion of the green spectrum from the visible range.  That pushes the light radiance in the camera to the twilight colors--purples, oranges, reds--we enjoy most. These are physical colors. We just removed a small portion integrated by the naked eye so it can emphasize warmer and cooler colors. And in fact, my memory of this sunset at Arches Natl Park is closer to the filtered photo.


Unfiltered sunset of Balanced Rock at Arches Natl Park

FL-W filter used at the same sunset moments later


The final sunset photo as the sky intensified to its peak and my memory of it. (FL-W filter)

More advanced optics can remove bland light and intensify unseen light, enhancing the sky's "imperceptivity" to our eye.  The radiance is a natural phenomena that our camera can sense with proper filtering, and reveal to our Next Eyes.  A bland sky at dawn can be translated into something far more appealing. (Side note: in camera HDR is not very appealing, this test showed.)


Visible (AWB, HDR in camera)


Visible with FL-W filter (FL WB, HDR in camera)


"Unseen" light with custom filter under development, cool and 
warm colors emphasized even more than with the FL-W


With filtering unseen light, it makes a drab sunsets/sunrise more amazing.  Over the course of one week in April 2017 at only a couple of miles from my home, from ordinary skies like the visible one above, I produced the following pre-/post-twilight photos that fall under imperceptivism because they capture unseen light that is physical. 

Each of these filtered photos is unaltered beyond custom White Balance, auto-levels, resize and a jotted signature.  The camera recorded these photos nearly entirely as presented using a custom optical filter.  And I have several dozens more like them from the past week on my camera right now.

sunset April 16, 2017

sunrise April 17, 2017


sunset April 17, 2017

sunset April 17, 2017


sunset April 19, 2017

sunset April 19, 2017


sunset April 21, 2017

SUNSET April 22, 2017


SUNSET April 22, 2017


SUNSET April 24, 2017

SUNSET April 24, 2017



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