Another question about IRAY.
AnotherUserName
Posts: 2,727
Hi everyone.
One of the things (there are more:)) that I still dont understand about IRAY is whether or not it is more efficient to completely encapsulate a scene, either with an HDRI dome or four walls, a floor and a ceiling, whatever, or is it better to leave elements like that out if they are not going to be in view?
Daz 3D is part of 
Connect
DAZ Productions, Inc.
7533 S Center View Ct #4664
West Jordan, UT 84084
Licensing Agreement | Terms of Service | Privacy Policy | EULA
© 2025 Daz Productions Inc. All Rights Reserved.
Comments
On one hand... because Iray uses Path Tracing it first calculates if a light ray will reach the camera and discards the ray if it vanishes out of the scene.
That means its better to leave walls and things out, so the path tracer will not have to calculate the extra bounces on a ray that is discarded.
On the other hand... Iray likes lots of light to build up the 'samples' so a wall reflecting light back into a scene may help.
...an HDR as a general light source is always good.
Lol, so its a case by case basis? How about this, suppose I like an HDR light source, but I dont want the background and want to use it in conjunction with a wall or two that may be in the scene? Does that create an issue of light being calculated that may be hitting the back of a wall? Or is that similar to what you said about the light being discarded?
The more light bounces the longer the render will take. The only thing that "bounces" against the Evironment dome is the ground shadow, and that's a very simple calculation, so it doesn't add much time.
If you take out walls and ceilings, just remember that these can contribute to the overall lighting of the scene, simply because they are bouncing light. A completely open set is the least realistic of all, because there's no light striking against anything. In the real world, bounce lighting contributes to the ambience, and aids realism.
Whether or not you use walls, floors, or a ceiling should ideally depend on the type of lighting you want. If you're getting slow renders, try decreasing the reflectance of the floors, walls, and ceilings. You can also try reducing the max ray paths settings in the Iray render Optimization subpanel. The default setting is -1, which means "infinite." You can set it to a specific number of ray bounhces. It usually needs to be at least 5-7 to avoid issues with black eyes and other artifacts.
Thanks guys, ive noticed that reflections do slow things down. So just to be specific, we are talking about the glossy reflectivity, correct? Not the actual light reflicting of of walls? Or is the one dependant on the other?
Glossy reflectance for one, but light colored objects also reflect more light than dark objects. A dark object that is fully matte (roughness set to 100 for example), will be seen in camera, but will bounce around much less light in multiple passes of the ray tracer. So, If you have some black wall somewhere, out of camera view, you might as well hide it when rendering. It doesn't contribute anything useful. But that's not a typical situation.
I will often hide scene furniture and characters if they aren't in view, but leave the walls, floor, and ceiling of the set more or less static, if possible. That gives better continuity of lighting between various camera angles. Of course, this is not important if you've set up a scene for a single shot.
Excellent. Thanks Tobor and prixat. Good info.
To add to Tobor's discussion, I have found that a "max ray paths settings" of 10 or 11 seems to be adequate for any scene I have tried. It will reduce render time on complex lightin scenes.