Dome Light and GI

[ValeroStudio]

So if you add a dome to your scene, is it supposed to replace your GI setup in your environment or should it be adding to it? Back in the old days of VRay 2.x I used to use a combination of VRay Sun GI and a dome light mixed with it to add some more 'life' into the scene lighting. Lately, I have come to the conclusion that when I add a dome light, it seems to disable that VRay Sun GI - is this normal behavior?

[konstantin_chaos]

Hi ValeroStudio,

The Dome doesn't disable the Sun & Sky system, it acts as an additional light source in the scene.
This means that if you throw in a dome the direct light from the Sun will kind of go through it and have an effect.

On the other hand by default the Dome blocks the environment light since it creates an imaginary sphere surrounding everything in the set.
The options of the light can change that behavior:
- Invisible - Enabling this option will make the Dome invisible for camera rays and you'll no longer see it in the background. At this point the background texture will appear in the back. You can use it to have a screen-placed background image while still illumination with the Dome
- Affect Reflections / Specular - Disabling the checkboxes will let you see the Reflection environment(or Background if the Refl. one is disabled) in material reflections instead of the dome. The options are useful if you need to illuminate with the dome but have another color or texture reflected (Sky for example)
- Affect Diffuse - Disabling the option will make the light invisible for lighting and GI rays. This option is not that useful since in most cases you want the dome to emit light.

Hope that helps.

Regards,
Konstantin

[ValeroStudio]

Got it. That's what I thought. Maybe my dome light values were too low and causing dark shadows - I played with it and I think I understand what I was doing wrong now. It works as expected. Thank you.

[kenancakir]

You can adjust the dome hdr sun position by rotating either horizantally or vertically if you make it invisible..

[ValeroStudio]

Here is an example of what I am speaking of. I added an HDRI but when I turn it on, the GI gets darker then when I have just the sun on. Isnt the dome light supposed to add to the GI regardless of its intensity value?

[kenancakir]

Somethimes i use both dome light and sun.. You have to uncheck the shadow of one, from sun or dome.. You will get softer shadows.. Two light sourcese cause dark shadows, it is normal..

[peerman]

It also depends on your HDRI. If it's an hdri of a studio setup with one white/bright area and the rest is black, then the shadow site won't be lit (or almost not). Could you show your hdri? I always turn off the sun when I use hdri and didn't see any significant darkening (but again this depends on the hdri chosen). I rarely add an extra pointlight or arealight to brighten up shady areas.

Best,
Peter

[ValeroStudio]

So here's an example, I create a dome of using an HDRI, leave it set to 1 and then click interactive. The shadows are dark, turn up the intensity, shadows look good, turn off the dome and you can see just the shadows from just the Sun. Now, based on how I understand how lighting should work, shouldn't the shadows always at least be as bright as they are with just the sun, even if the HDRI intensity is too low? Isn't the light contribution additive?

The simple solution is just turn up the HDRI, and that's fine, but I am wondering if the dome light isn't working the way it should and somehow turning off the GI from the sun and not adding to it.

Here is the HDRI if you want to test for yourself.
https://www.dropbox.com/s/mna8uoio3r..._free.hdr?dl=0

[ana.nedyalkova]

Hello, Matthew Valero,

In addition to all advice in the previous posts I would like to add that when lighting a scene with V-Ray Sun and Dome light(with HDRI) simultaneously you have to be aware that the emit sources of the two lights might not have the same direction - it depends on where the sun (light source) is positioned on the HRDI image - this can be amended by manually rotating the Dome or the HDRI texture itself. The intensity of the HDRI will depend on the HDRI quality and on the setting of the physical camera used. The EV set will have to be changed if used for Dome Light with HDRI.
When combined, the intensity of one of the two light sources has to be corrected.
The intensity of the shadows is affected by the direct light source, the GI and the surrounding objects’ materials. When you add a Dome light in a scene, this affects the GI and shadowed areas become brighter.
If you want to be able to control the color or intensity of the shadow with that type of setup you can always use a Wrapper material(applied on the base box/plane). Then you can change
Wrapper > GI Affect > Receive GI of this object but you should be aware this will also affect appearance of the whole object - so it may not be ideal scenario.
Keep in mind that the physically correct workflow will be to use either V-Ray Sun or HDRI type of lighting. In case you’d like to have environment image you can simply use an image in the environment background slot.
We’ll be hosting webinar tomorrow which will cover some of this subject. Here is a link to register: https://www.chaosgroup.com/vray/sket...r-october-2018


Kind regards,
Ana