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Diurnal Changes in Spectral Distribution of Sunlight

Discussion in 'The Cave' started by Ed Pomicter, Jun 13, 2019 at 4:15 PM.

  1. Ed Pomicter

    Ed Pomicter New Member

    This slide of Wunsch comes up frequently, but I think it has been misread at times. The bar at the bottom of the photo does not represent the color temperature at those times of day but rather is a key to the color temperature of the color graduations of the middle band of the slide....red moving through white to blue back to white and finally to red. More specifically, the color temperature at the end of the day is not 16000K, but rather 1800k as it is at sunrise. The noon color temperature is in the 10000-16000K range as represented by the blue color under the tree.

    diurnal changes in spectral distribution of sunlight.jpg
    countingstarsx, JanSz and Lahelada like this.
  2. Bob Stirling

    Bob Stirling Silver

    I understand thanks, the colour bar is a Legend.
  3. Sue-UK

    Sue-UK Gold

    I think there's a difference in colour temperature between sunrise and sunset, because of the transitions out of and into darkness. At sunrise we are coming out of darkness and there is enough blue to signal, which I'd assumed the 1800K reflected. From that I assumed the noon colour temperature of around 5500 to 8000 reflects the more even spread of all the spectral frequencies compared to sunrise and sunset. Near sunset and especially during twilight, "absorption by ozone (O3) significantly contributes to maintaining blue color in the evening sky." (source wiki). So compared to the amounts of blue at sunrise and at noon in relation to other frequencies present, other frequencies dropping off and/or not being maintained by ozone as the earth rotates and night draws in, together with a gradually increasing saturation of (non melatonin suppressing) natural blue, may be "hotter" in terms of describing sunset frequencies using colour temperature, but sedating using what Wunsch has discussed about the different biological effects of saturation of blue and red. I hadn't questioned Alexander Wunsch's figures because although sunrise and sunset look similar, (camera), differences in colour temperature seem to be involved in distinguishing between the two for clock function /circadian rhythm. :)
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  4. Sue-UK

    Sue-UK Gold

    Posting a link to this before I lose it, as I need to dig deeper .... https://www.facebook.com/drjackkruse/posts/1310514499012901/
    "The color temperature of the sun changes as the day progresses. So in the AM sunrise the color temperature of light is only 1800 Kelvin, at 10 AM it is 4000 K, at solar noon it is 5500 K, at high noon (12-1:30PM) it rises to 12,000 K, and at dusk it is 16,000K. It builds as the day goes on. It is not linked to the frequencies of light as many expect. "
    Alex97232, JanSz and Lahelada like this.
  5. Ed Pomicter

    Ed Pomicter New Member

    Thus the reason I started this thread. I believe that statement is based on a misread of this slide, and I am happy to be corrected, but all of the reference data that I can find states that sunset color temp is similar to sunrise color temp. Why would it not be? The sun radiates a "constant" output over the length of a day, with the variables being the angle of incidence of the light on the earth's atmosphere, the thickness of atmosphere that the light penetrates, and the moisture/cloud/geoengineering present in the sky. If I had a spectroscope, I would confirm with self measured data points :)

    Last edited: Jun 16, 2019 at 4:34 AM
  6. JanSz

    JanSz Gold

    On one hand it looks like the slide was mis-red.
    On other hand it would not be a first surprise.
    Only @Jack Kruse can clarify this.

  7. Sue-UK

    Sue-UK Gold

    If the reference data out there is all based on frequencies of light, on what it is measuring the figures could be right, but if the correct colour temperature measurement contains a variable not connected to light frequencies, the answer is wrong. A bit like a bowl of fruit containing both apples and oranges, but only counting the apples. :D But if sunrise frequencies turn certain hormones on, and UV turns them off, (or adjusts the volume switch seasonally), what happens to circadian control if the sunset "recipe" is the same? I would suspect this would cause circadian signalling disruption to diurnal, nocturnal and crepuscular species. If the differences between sunrise and sunset colour temp isn't based on light, basing my variable on a different aspect of light (colour saturation) doesn't explain it. If its anything to do with things like black body temperature changes or Planckian locus,:confused: you could write my understanding about that side of physics on the back of a postage stamp - in large letters. :D
    Alex97232 likes this.
  8. Sue-UK

    Sue-UK Gold

    From https://forum.jackkruse.com/index.php?threads/why-is-am-sun-the-most-important.21611/#post-272724

    Thanks @Sajid Mahmood :)

    Sajid Mahmood likes this.
  9. Saichi

    Saichi New Member

    Sunsets are not blue/16,000.

  10. My matchbook is much smaller than yours, but here's a thought. Becker talks abour how in migrating birds, the sun light is the primary info source but reverts to magnetism when sun is blocked by clouds (or the earth). Might our bodies be sensing the balance between light and magnetism? Or changes in the balance? As the sun goes down, do our bodies search or wait for some other info or energy from the earth or universe? Im guessing we are deadening our perception of the universe by blinding ourselves with light at night, especially during the transition, when we should be locking on to our night signal.

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