Cycles renders suddenly darker (Kitchen)

Hello together,

I´m working on a project, that I recently declared as completed - by far not perfect but finished for me as a bloody beginner. The last days I thought it might be worth being improved. I basically rebuilt the whole scene and made some testrenders every now and then. One day cycles renders came out much darker than before and I don´t know why. I think I messed up some render settings, but I can´t find the suspect. Here is a testrender from when it all was good and bright:

Then I added some objects and the renders got by far darker. Perhaps I also changed some settings, but I definitely can´t say which. After trying to clean up the mess I now get this result:

These images were made with an HDRI strength of 150. Even when I rise the strength to 10000 it doesn´t get much brighter.

Any ideas what could be wrong with my settings?

Thank you for your help!

First suspect that comes to mind is the window glass panes - are they letting enough light through? Next suspect is surface normals. Using materials with completely broken surface normal modifications can bounce/reflect light in completely havoc directions.

Thank you CarlG! :partying_face: The normals were almost correct. Flipping the few wrong ones didn´t change anything. The window glass material was the problem. Don´t know when I messed that up :man_shrugging: I had an alpha value of 1.000. After turning it down to 0.000 it looks good now (with an HDRI strength of 10):

My glass material looks like this:

I think it looks quite good in the renders (from different camera positions). If you have any ideas for improvement, please let me know.

And here is the next question: why are the chairs partially black from this perspective? From other positions it looks as it should. They have a light grey fabric texture. Normals are ok btw.

Thank you!

I don’t think you should set a zero alpha in a principled shader. This setup is more physically correct and will allow light to pass through.

That was really quick, thank you! :slightly_smiling_face: I´ll definitely try that!
Can you tell me why I should not set alpha to 0? As I already mentioned, I´m an absolute noob with 3d software like blender. I tried different values between 0 an 1 and for low values < 0.2 there was no significant difference - from my point of view.

In the light path trick above, I never use the reflection ray, only the shadow ray - but that’s just me. I also tend to use layer wiehgt/facing through a RGB curves node to control the Transparency shader color. Similar to how glass is more transparent to our eyes at facing angles, so is it to light. This is only nitpicking and could easily be ignored without much impact on the final result. White or slightly below is good enough.

Not only the normal facing direction (affects the fresnel node, but I think Principled has fix for it builtin), but also the modifications done to them. Could be bad normal map data/usage or bad custom split normal data as examples. I’ve seen both in downloaded and imported objects.

Hello CarlG,

I´m a little confused now. Are you talking about the glass problem or the chair texture problem?
Thank you.

None in particular. Just generalizing. Are the chairs working now? A quick way of checking normals is to use a sharp glossy and check if the reflections “makes sense”.

Thanks to you CarlG, I dind´t give up searching for the problem with the chairs and finally I got it working the way I want. :smile:

The problem were not the normals themselves, but the correct connection of the bump image node to the bump node. I had it connected to the Normals input of the bump node instead of the height. Don´t know why I didn´t notice that earlier. :roll_eyes: Now everything looks fine.

Thank you all for your help!

Yeah the nodes are a bit stupid in this sense. They’re unable to “sense” what is being plugged in and choose an appropriate socket when dropped in between nodes.