Setting manual sun intensity?

[C.Murphy]

I noticed that when I click on the sun generated by Gensky or Gendaylit, Blender shows that the intensity of the sun is only 3 W/m^2, when in reality it is closer to 1000 W/m^2.

For my current project, I need to set the intensity manually to 1366 W/m^2.

Does anyone know how this can be done and how to ensure that the affect will be accurate when Blender does not show the true value?

[Ole Marius Svendsen]

As i think this inquiry is related to your last post about some calculation in outer space, and not earth radiation. What if you use a climate file, which you modify and overrite the EPW file with the sun constant? 

[VI-Suite]

Blender sun settings are separate from the LiVi Context settings.

If you want to set 1366W/m2 then look up the use of Radiance's gensky command to generate the sun description with the desired intensity. You can then replace the LiVi Context sky description with the gensky output with a Text Edit node.

LiVi won't calculate thermals though. Ole is correct, you can use an editor to replace the solar intensity in an hourly EPW file for thermal analysis with EnVi/EnergyPlus  but EnergyPlus is designed to model buildings and you would have to make other changes to make the sun position constant and to eliminate convection from your calculations. Your metal box would also need to hollow like a room. All of this takes EnergyPlus out of the realm it was designed for however, and the mathematical assumptions it uses may become invalid. You would probably be better off with some kind of finite element analysis tool. LiVi could be used to generate the radiation boundary conditions for such a model, but if it's just a box you could calculate incident radiation based on angle of incidence quite easily without it.

In short, good luck but it will take some work to get EnergyPlus to do it, even if it can, and there would be no guarantee that the results are realistic.

[C.Murphy]

Thank you for the idea! I copied and opened one of the EPW files in the EPFiles\Weather folder and found a disambiguation of the data columns here: https://designbuilder.co.uk/cahelp/Content/EnergyPlusWeatherFileFormat.htm
Please correct me if I'm wrong. I think that "Direct Normal Radiation" and "Direct Normal Illuminance" are the values I need to change to the desired sun intensity, then I would need to set any "Diffuse Horizontal ..." values to 0, so that light is only coming from the sun. Am I understanding this correctly?

This might be a bug, but the new .epw file in that folder does not show up in the EPW dropdown list in the VI location node. I restarted Blender a few times and deleted and replaced the location node. I searched the user-manual for quite some time and checked Ryan Southall's tutorials for a procedure for adding EPW files. Perhaps I overlooked something.

[C.Murphy]

It seems like the text editor approach will work for what we're trying to do. There is just a little more clarification needed to make sure it's being used correctly.

Below, I deleted all sky related functions and achieved the confidence-inspiring result below. What's left is what I assume is generated by the +s callout as per the manual.
I couldn't find "void light solar" or "solar source sun" in either the LiVi manual or the Radiance manual (linked below) to verify the units. Are these functions explained somewhere else, and am I correct in assuming Watts/Sterrandian/m^2?

Lastly, "solar source sun" seems to define the angle and intensity of the sun. Would it be correct to assume that for accurate values, 0.5 should be changed to 1?

Edited Text:

Node Setup:

Resulting render of a metallic smooth-shaded monkey head with and without sky:

Manuals I have been using:

https://bpb-eu-w2.wpmucdn.com/blogs.brighton.ac.uk/dist/3/21/files/2023/12/vi07_0_3.pdf

https://www.radiance-online.org/learning/documentation/manual-pages/pdfs/man1all.pdf

[VI-Suite]

You can give Suzanne a sensing material to see if you're getting the irradiance you want.

[C.Murphy]

Thank you for the idea. I did something similar by making a 1 meter square surface oriented perpendicular to the sun. Without any sky, changing the value from 0.5 to 1 resulted in a W/m^2 very close to what is expected without an atmosphere, although, for completeness of the research paper, it would be great to understand why this is and what the units are for each of the 3 wavelengths. It doesn't appear to be documented in any of the manuals I have read.