I want to know the precise spectra density of light we humans (and plants) are exposed to at various times throughout the day from morning to evening. I'm searching for spectral density graphs/spreadsheets on early morning daylight, noon daylight, evening daylight, etc. as (measured from around sea-level or anywhere on Earth's terrestrial surface in the USA or similar). I'm finding it very difficult to find this kind of raw data, and I know it has to be somewhere on the internet. I'm still inexperienced in research, and I've been spoiled by the ease of Google all my life. Any help would be much appreciated.

Thank you very much.

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    $\begingroup$ Connected question: On the light difference between morning and afternoon... but no such data there either :( $\endgroup$ Commented Sep 25, 2022 at 2:18
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    $\begingroup$ What is spectral density? What units? Irradiance? $\endgroup$
    – miguelfg
    Commented Sep 25, 2022 at 7:22
  • $\begingroup$ @miguelfg I don't think it's necessary for the OP to commit to some specific units ahead of time. Let's just wait and see what data is actually available. The various units for light measurement are vast and complicated and quite a challenge to wade through. It's going to be per unit area per unit wavelength, but whether they want it per unit solid angle as well or integrated over the whole sky instead, that may not be a choice. $\endgroup$
    – uhoh
    Commented Sep 25, 2022 at 9:39
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    $\begingroup$ @ArielHernandez Welcome to Earth Science Stack Exchange! It will be helpful to know how you're going to use this information. Most of the daylight comes directly from the Sun, especially on sunny days, but there's an important contribution from the blue sky and the clouds as well. How are you going to be using this information? A rendering engine for realistic animations? Solar power estimations? Energy available for plants? The more you can explain, possibly the more helpful the answers will be. $\endgroup$
    – uhoh
    Commented Sep 25, 2022 at 9:43

1 Answer 1


You probably can take the data outputs of this awesome tool to your problem. It is the Photovoltaic Geographical Information System , designed to calculate solar energy input to photovoltaic instasllations. But on the right of the map, you have a vertical menu to choose between monthly, daily, hourly, and year data.

First choose location in the map, you can display global irradiance, only direct light, and more. You can also play with inclinations and horizon shadows, losses, temperatures,...

It is very complete, so probably it worths to look at the documnetation linked in the horizontal menu.


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