Cineversity

I’m trying to simulate some directional stage lighting in a scene. Using physical renderer with global illumination activated.  I’ve loaded IES files into a light object, and have “Ambient illumination” and “GI Illumination” checked for the light. If “visible light” is set to “none” then I primarily see just the spot where the light hits objects (the stage). I get no realistic secondary or ambient light spreading around the space from that light object as I would in real life. It leaves all but the specific spot dark (and the spot itself is not very well lit).

BUT: if I set “Visible Light” to Volumetric, I get all the ambient illumination from that single light source that would (in real life) bounce around and help illuminate the whole space. That is what I want. HOWEVER: I would like to have that ambient, GI-type light without having the actual volumetric cone that appears as an unrealistically bright white cone coming from the light.

Any way to keep the spilling light but get rid of the cone?

See jpg attached for clarification. THANKS in advance for ANY help…

Hi jrhans,

The cone is normally like a light source in its own right, as it is based in reality on particles (dust and moisture) in the air, which reflects [or refracts] the light randomly. If you take that out, the light needed to illuminate secondary objects must be then much larger.

First, let me clear some terms:

Ambient Illumination, means that with an omni light, everything will be lit equally, only shadow and falloff can change it. It is normally an effect to elevate the base illumination of a set. Which means, it takes OUT all contrast the stronger it gets. However, it has nothing to do with the idea of inheriting light to the context, for example.

The “Physical Render”, it does not deliver a light calculation that would provide a calculation on frequency (as in nano-meter) of the light nor does it counts photons. It is a way to get photographic effects simulated, as in motion blur or depth of filed and to a certain degree to produce an equivalent of the artifacts of a lens, to name the main area.

Global illumination is a system that tries to accomplish, with the limited computer power we normally have, to come as close as possible with the distribution of light based on, e.g., surfaces. The light, as in IES might be defined by realistic measurements, and as far as possible, it will be re-created. There are limitations, as long as we do not volumetric measurements of the light distribution in space. Those lights can only work, if the context in which they are used is scaled correctly, and the surfaces are set up accordingly. The quality of any surface and how it reflects the light is also just a simulation and not an one-to-on equivalent of the reality, which would be again, and extreme effort for the calculation to reproduce it. As light bounces around with no limitation, only entropy will stop it to provide brightness, this is an nearly endless bounce in reality. Impossible for any algorithm to reproduce, ...any!

Having that out of the way, the set up of your scene is crucial, and each part of the light should be set up as well. This can’t be evaluated from a jpeg. I can take a look into the scene, but I might need a data sheet for the IES light to understand what light is really wanted here and if the set up works.

To make a point here, please load the scene file below, render it in standard and physical, each time with and with out Global illumination on or off. Have a look if the cube is visible or not in each case. I have not changed any default material nor objects here, so the idea is purely to check that it is working on your side.
EDIT: The second file is to showcase the “Cone”. Please render here with Global Illumintion on and off, as well the Volumetric light in the light source on and “none”. The floor is shut off to keep the results clean. /edit

If I could have your scene, limited to the light and the stage, I could have a look into it. If it is a NDA case, I can create an upload link, or you send via PM a download option. Include in any case the data sheet of the light! Otherwise we can use any Light source from C4D that mimics this light, IES without data is kind of meaningless as you certainly know.

All the best

Here the second file I added into the description:

Thank you so much for your thorough response.

Your clarifications on Ambient Illumination and GI were very helpful. I should have begun by stating that I am looking for the overall visual effect demonstrated in the attachment as opposed to anything particularly realistic or technically accurate. Nonetheless, thanks to your response and bit of bungling around on my part, I think I’ve found a suitable solution.

Thanks again for a prompt response!

Thanks for the reply, jrhans!

The initial question lead me a little bit to believe that this is more about accurate simulation, than a VFX question. Sorry if I missed that point.

As I write in a forum, I try to cover things more in detail. More detailed than the one who asks perhaps need. But I’m not in the judging of knowledge business, I’m just sharing what I think will cover a theme for an audience.

If you have found what you need, I’m happy about. If there is any question that would benefit from a different discussion, I’m happy to have a look into it. Stage lighting was my first art form, which I did over 4 years with 135 gigs for rock and jazz bands, way back in time, nothing but great memories from that time!)

My best wishes for the project.

Yes, I was obscure in my original post. I did appreciate the detail in your response. The information will continue to be useful.
At some point I would like to explore a discussion of how best to set up C4D for accurate simulation of stage lighting for the sake of conceptualizing and designing. I would like to pick your brain on that subject when I have a little more time to devote to it—if your time and inclination permit.

By the way, I also followed your youtube playlist link for a quick look and there seems to be a lot of very useful content there that I will explore at some point as well.

Thank you again.

Best wishes

ps- attached is the project file, if you have any suggestions on setting up more accurately… The ies file is for a SourceFour Par medium flood. But again, I am doing OK with what I have if your time is better used elsewhere.

Thanks for the file, jrhans, I will look into it

Thanks as well for the nice feedback on my YouTube material, we decided to post it publicly, so the “pipeline” between Photographers and VFX/CG/3D artist is better support. Even I think photographers should learn 3D as it is the next step after video ;o)—in the same way I think photography knowledge (in depth) will support most 3D work.

My best wises, and yes, please ask and time is avaialble!

It seems that if I increase the gamma setting on GI in the render settings, I get a visual result that more closely approximates the overall intensity of the actual floodlight. But again, that works form my scene on a visual level but I don’t know what it does to the other aspects of the 3D light’s accuracy.

Light works in a linear way. Not in gamma. To change this value might please your eye or create something that you are after artistically, but in the moment you touch that parameter, the idea of natural light is just gone.

The problem with light and perception is, that it works in different ways. Humans have a tendency to focus on something and adapt to it. Any value above or below is then not perceived as is anymore. Add one light and the eyes adjust, and the twice amount of light is not perceived as double, and the more single lights you add the less it will be noticed. Think of hundred candles in a room, add one, might not be as effective as when we had on one to start with. I simplify here, but that is in a nutshell the linear light vs. human perception: Hence the Gamma curve.

Light on the other hand increases the intensity with doubling it in a linear way. This works in low light as in bright Sunlight, twice the source, will double the intensity.

So, if someone suggest to use the Gamma slider, then the only truth is, it is an aesthetically call, not something that has anything to do with real physics.
Think of the gamma as a curve adjustment, where the white and black point are untouched, and the middle value is moved. So far so good, some might even like it. But what is really the white point? Some might tell you something about, but it is not even clear to the people who write color science for the leading organizations, e.g., SMPTE. I took three course from one of them, so I was able to ask him first hand: Charles Poynton. There is the reason why most people think the highlights are just white, well, if one clips them at 100%, no wonder. But it goes even worse, which is not discussed by most leading people even. How does the curve continues after 100% or 1.0? There it bites the results, to give a short answer. So, just adjusting the gamma, not my taste of quality, nor my idea at all. Light has to be set, material has to be set and with the camera Point of view in mind, you get what you need, without messing with the gamma. If you stayed all the time in 8 or 16 bit, the distribution of values is relatively fixed, and messing with the gamma, even in the GI settings, might cause banding if you change your mind after rendering. Again, I pour here a lot of details, and I know it is not a simple theme, so my suggestion, focus on the light, material and camera, there the magic starts, not in the gamma setting, never has, never will.

Based on that, roughly a decade ago things started to change, and even textures in 3D changed. In the moment the gamma of an image were left in the scene, the rendering result might applied it again. Or even worse, the light reflected from that gamma based surface is of course “gamma-distorted” and if global Illumination bounce a several times around, the effect leads to the CGish feel, in a nut shell, to absolute incorrect (physical) results.

Cinema 4D is based on linear calculations inside, but of course, this can break based on user input.

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Home made accuracy: take the materials that you like to simulate and photograph it with a MacBeth chart from different angles, then apply the color science of the color chart to it and set up the material in the Cinema 4D scene as close as possible. This is not accurate, but certainly more often than not more accurate than eye-balling. Again, the human eye adapts and is adjusting to a most situations. It is more complex, especially with reflective and fresnel values… but that is not the moment to discuss here.

A hint, if you use 3rd part textures and they do not provide background information how they produced it, you are perhaps out of luck anyway.

Eventually—I go too much into details again, but if you like to pre-visualize anything, you need to stay in the parameters and dependencies of the game in the first place. Pulling a gamma, how to do that on a stage? ;o)

P.S.: just a note to my future self:  https://www.routledge.com/products/9781138913684