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I'm trying to model my apartment for a restoration. I can't get the outdoor natural light of the sun. The scene remains always too dark and full of noise fireflies.

Real Photo Outdoor Lighting

As you can see from the photos the sun was not even so bright, but the interior of the apartment is completly lit.

This is the result of my render: Render I'm using an HDRI image as env. texture.

Can someone fixing this scene, dark room and noise? Has blender a limit?

I really couldn't find any answer, every similar question on internet has no answer.

I tried to tweak the exposure value, env. texture strength, light bounces, light clamping, sky texture, portals on windows, transparent material for windows with no results.

I'd prefer not using fake lamps but let blender simulate the natural light physics.

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  • $\begingroup$ Hello and welcome. 3D light is not like real world light, so, most of the time you need to use more than one light source to achieve real world lights. Sometimes you will also going to need to open walls that are not going to be visible to the HDRI light go inside. $\endgroup$
    – Emir
    Oct 24, 2023 at 2:12
  • $\begingroup$ Thank Emir. This is a so common setup scene. Seems strange that Blender can’t handle it $\endgroup$
    – Umbe Bagna
    Oct 24, 2023 at 6:01
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    $\begingroup$ I answered a similar question once. First of all, if you light an interior scene just with outside lighting, the light has to bounce around a lot on the walls to light it up like in real life and this of course introduces noise which you have to battle with samples and/or denoising. However you can get "realistic" lighting with HDRIs, but you have to keep in mind the real sun & sky are very, very, very bright. See my answer here: HDRI lighting too dark and HDR image just acting odd $\endgroup$ Oct 25, 2023 at 10:34
  • $\begingroup$ As an addition (didn't fit in the first comment): direct sunlight at noon has a strength of around 1000 W/m², the unit W/m² is used in Blender's Sun lamp so that is a Strength of 1000. The shade under a blue cloudless sky is still 160 W/m², an overcast day 10 to 20 W/m². So in order to get "realistic" lighting you have to increase the world strength a lot. But how much depends on the dynamic range and exposure of the HDRI which can vary from image to image. $\endgroup$ Oct 25, 2023 at 10:44
  • $\begingroup$ Hello. Umbe.. welcome.. please let us know here if @GordonBrinkmann 's answer has cleared this up for you, or edit your post to show what is not covered by it. $\endgroup$
    – Robin Betts
    Oct 30, 2023 at 6:26

2 Answers 2

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Hello dear Blender community,

After days of tries and reasearch, i don't know i managed to achive the goal. I mean i don't know exaclty which step was the key for a better illumination, but let me explain what i did and passed from this: enter image description here

To this:

enter image description here

Explanation

  1. Place the portals correctly: When using the portal function on area lamps it's important to place them the right way. They should be placed between the light emitter and the hole in the wall, not inside the room.

Like this: enter image description here

  1. Use a good HDRI: Use the filter "Top download" to search a good HDRI image with 22 or more EV. I set the strength of my HDRI to 40

  2. Adjust exposition to you desired value: In Blender go to "Render Properties" > "Color Managment"

  3. Set "Filmic" in View Transform and "High to Medium Contrast" in look: You can find this parameters in the same tab of poit .4

  4. I used only transparent shader for windows but i'll make soe experiments mixing it with glass.

  5. Raise a bit the "Max bounce" settings: enter image description here

  6. I set my render sampling to 1024, i have a little noise but for the final render i'll cranck it to 4096. Rendering time 5mins more or less.

If i forgot something I'll update this answer. Please leave you opinions, and let me know if you need the .blend file.

Thanks to the whole community and especially to @Gordon Brinkmann and @Emir that dedicated his time to my problem

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A few other interesting things in addition to your own answer:

Ray-filtered Glass Shader

Set your windows' glass shader to be fully transparent for all rays except shadows and reflections. (example)

If you use a Glass shader:

enter image description here

If you use the Principled Shader (not 100% sure of the accuracy on this one, would love an expert's word on it):

enter image description here

Comparison:

enter image description here

Clamping

By default, Blender have its Direct Light Clamping disabled (zero) which is often optimal, but its Indirect Light Clamping is set to 10. Increasing this value or disabling it (set to zero) helps light entering the scene, at the cost of noise and fireflies (but a good denoising usually does the trick for that).

enter image description here

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