VRay Light Feature (Emit GI only)

[stevejjd]

Hey guys

I wish that there was a button for a vray light that made the light shoot out bounce light (GI) instead of direct light. This would be an easy way to create ultra soft lights. Is this even possible?

Thanks

Steve ~

[MANUEL_MOUSIOL]

What would be the difference in rays? A ray is a ray (is a ray is Ray.. . )
Bounce light is already bounced off an object so the rays don't come from the light itself anymore.
If you want soft shadows, just make Your light larger

[stevejjd]

I found out how to do it from the Mastering CGI website, lighting lesson.

[andy51]

Turn off GI and use VRayAmbientLight, it's not a direct light, so could give you the effect you are looking for... but what do I know, I have never tried it myself

[rikou]

I found out how to do it from the Mastering CGI website, lighting lesson.

So can you tell us how to do it, please ?
Thanks !

[MANUEL_MOUSIOL]

So only gi is computed from the light and primary rays are ignored?

[stevejjd]

It would be best if you look at the Mastering CGI lighting lesson 5, Part 2, Lighting Statue. (The tutorial does not show how to make lights that fire GI only)

Firstly I will explain what lighting effect is desired. Consider a scene with a large marble statue. Imagine that the statue is lit from the screen left and so has a strong shadow on screen right. Now we want to be able to have a very soft light on the shadow side. Using a light to directly shine on the shadow side is too strong. The solution is to use a bounce light so that really soft, diffuse GI light is whats illuminating the shadow side.

So the way to do it is with bounce cards (Reflectors). Instead of aiming the light at your subject directly, you aim it at a reflector. The bounce light from that will fill the shadow side with incredibly soft light. You can see how much more soft the bounce light is as compared to a direct light in the render passes (VrayLighting pass and the V-Ray Global Illumination pass). The VrayLighting pass will show only the direct light that has bounced once and the GI pass shows only the bounced light which is often much more soft and subtle than the direct light.

A reflector can be as simple as a Box or Disk or as complex as a large fabric drape.. The colour of the reflector can be a diffuse, white or grey but you can also make metallic ones that resemble silver or gold. Note that you can better to focus the light to hit only the reflector by increasing the 'Directional' value. You can also group the light with the reflector so its like moving a singular object for easier placement. Experiment by turning off the lights that directly hit the object and only lighting it with GI.


Lighting with reflectors makes heavy use of Global Illumination, so big downside is that you have to set the GI engine to Brute Force + Brute Force and the bounces up to 15 bounces. So this can take a huge toll on render times.


With this said, I wanted to ask Chaos could make some way to get the same effect without the massive toll on computation......like for, example, a setting in the V-Ray light that would make the light emit GI only and not direct light.


I will update this answer later...I'm just stuck today with a lot of stuff.

[benb32]

I'm not sure I understand...? Every material/surface (excluding 0,0,0 - which isn't physically accurate) is a GI emitter thus a GI light. Try to replicate how a photographer would lighten a scene, just like you mentioned with the bounce cards. As it's the GI that will be softening your shadow there shouldn't be any reason to change from LC+BF. So performance should not be too much different - if you make you bounce card big enough the biggest contribution to lightening/softening your shadow will be the 1st bounce GI anyway. No need to increase the bounce too high, it would only artificially lighten the scene by including stray GI bounces from everything else - plus as you said make render times inordinately long.

[MANUEL_MOUSIOL]

Why not use e.g. a rounded geometry as a light to spread the rays and maybe add a soft box-like hdri as a map to make it uneven?

[kosso_olli]

It would be best if you look at the Mastering CGI lighting lesson 5, Part 2, Lighting Statue. Lighting with reflectors makes heavy use of Global Illumination, so big downside is that you have to set the GI engine to Brute Force + Brute Force and the bounces up to 15 bounces. So this can take a huge toll on render times.

Ah, that Warwick guy never fails to make a render slow. Either it's shaders with half a dozens of coats inside a blend to create a black plastic material, or GI in BF+BF mode, "to make it look pretty". Yeah, right.

In my entire life never did I need an indirectly lit reflector card to get some soft light onto a model. When rendering products or cars in a studio (pretty much half of the work I do), I only use V-Ray area lights. If the lighting is to harsh for a soft rim light, I simply put a soft gradient on it, and make the light larger and reduce it's intensity.
Using reflector cards, jeezz...

[andy51]

Could also use VRaySoftBox

[stevejjd]

Thanks for the feedback guys