Illumination Problem

[friscokid]

Hi,
I have a problem getting smaller light sources to cast realistic illumination to other objects without making the light sources extremely bright.
Additionally I get some confusing results when changing the Ray epsilon parameter with PT kernel.

All of the following renders were created with the C4D Plugin and Octane version 2.23.2 using path tracing.

Image 1 shows the displays with the disered brightness of the background pane emitters and a glass panel as cover. Unfortuenately this version doesn't illuminate the surounding objects at all, which doesn't seem to be realistic.

1. only one emitter, with glass

Image 2 shows the displays with another much brighter emitter that I put on top of the initial emitter and which is set to be invisible for the camera. This second emitter is very bright and therefore casts the desired illumination to other objects like buttons, case, floor, fader.

2. no glass, additional emitter

Image 3 shows the same setup as image 2, except that I set the glass panel visible again. This unfortunately makes the second emitter that was set to be invisible for the camera, visible again, because emitters behind glass just ignore the visbility setting in octane. This version is unusable because the visible emitter is extremly bright.

3. two emitters, with glas

Now I'm screwed, because I have no idea how to keep the not too bright background of the basic emitter of image 1 and have some nice illumination of other objects like in image 2 and also keep the glass pane (which sets the brighter emitter visible again).

In fact I don't understand in general why I have to set the emitters to be that bright to make them illuminate neighbouring objects. That seems unrealistic to me.
From everything I can see in reality, a light source with the brightness of the displays as you can see in image 1, should illuminate other objects, that are close. But in Octane they don't.
Instead I have to use emitters that are as bright as laser swords to get some nice illumination.

Probably I'm doing something wrong.
So, any help appreciated.


Another issue that is quite confusing to me is the influence of the Ray epsilon parameter.
Image 4 below is the exact same render as image 1 except that the Ray epsilon value in the first image is set to 0.000001 and in image 4 it is set to 0.001.

4. same as 1. but with Ray epsilon 0.001

As you can see, the glass pane and especially the the rings around the knobs look totally different. Actually almost all the objects that have a specular material assigned or that are emitting lights look totally different depending on the Ray epsilon value.
The results I get are quite random, so I have no clue which value to use to get some moreless physically correct results.

If somebody could shed some light on this, it would be very helpful to me.

Thanks in advance!

[ristoraven]

Try PMC kernel.. ?

[sadece]

is the "Alpha Shadows" enabled or disabled? also how about the specular depth value?

[bepeg4d]

and instead of one emitter and one specular object, why not use only the emissive option of the sss medium node in the specular material?
Also playing with the sampling rate could drastically change the result.
ciao beppe

[friscokid]

Try PMC kernel.. ?

Same problem with PMC

is the "Alpha Shadows" enabled or disabled? also how about the specular depth value?

Alpha Shadows is enabled, but disabling it makes no difference.

and instead of one emitter and one specular object, why not use only the emissive option of the sss medium node in the specular material?

Because there has to be a distance between the actual emitting back pane and the glass top. If I make the specular material emitting light, then it would look like the glass top would be the light source and not the object that is located about 1cm behind the glass.

Also playing with the sampling rate could drastically change the result.

I've tried a lot of sample rate values between 20 and 10000.
It actually changes how much time is spend to render the illuminations noise free compared to other light sources, but it doesn't make the illumination brighter without making the light source brighter too.

[friscokid]

This is another example that shows my problem very clearly.
My object has a lot of small light sources. I disabled all other external light sources that illuminate the object.
As you can see the light sources of the object itself don't cast any visible illumination.
In reality if you had an object like this with those light sources in a dark room, the light sources would illuminate the other parts of the object and the closer environment.
In my render however nothing gets visibly illuminated by the light sources. Not the other parts of the object, nor the table or the walls, just nothing.

only emitters, environment dark

If I want the light sources to illuminate other parts of the object, I have to turn them that bright, that all the LEDs and displays just look like that had bright white light sources.
This can't be the way to good.

I'm happy for any hint or advice what I could try to get the lights to behave more like in reality.

Thank you

[roeland]

Going over the suggestions: switching to another kernel (PT, PMC) will not make a difference. In fact, PT and PMC should render the same image (but the noise will be different).

The same for the sample rate parameter. It doesn't change the final rendered image, but it will change the noise in the direct light from that light source. In most scenes it can be left at 1.0 for all light sources.

Alpha shadows can be disabled if you know there are no transparent objects which would otherwise cast a shadow (this includes glass with fake shadows enabled, aka. architectural glass). In this scene you should enable fake shadows on the glass pane and leave alpha shadows enabled. And depending on how exactly you model the amp, it may help to increase the depth values.

Ray epsilon is important, and for this scene it should be set to a low value (definitely smaller than the thickness of your glass panes).

As for the original question: Are the displays supposed to cast any visible illumination? How bright are they supposed to be?

My guess is you are indeed not supposed to see much illumination. If you have for instance a TV computer screen, it will only cast a faint glow on anything right in front of it, and that's because the entire surface is emitting light. The light would be more visible in a dark room, but your scene doesn't appear to be dark.

On the other hand, some appliances (even some computer screens) have bright LEDs to indicate they are switched on. Those cast a little bit of illumination to their surroundings. Their brightness also makes them painful to the eyes.

But in the last image you posted, I would expect some illumination on the knobs around the displays. What kind of material do you have on the knobs?

--
Roeland

[friscokid]

In this scene you should enable fake shadows on the glass pane and leave alpha shadows enabled

That's my current setting.

it may help to increase the depth values.

If you mean Diffuse and Specular Depth, there is no real difference starting from a value of 10.

Ray epsilon is important, and for this scene it should be set to a low value (definitely smaller than the thickness of your glass panes).

If I set it to the smallest possible value it works best for me to avoid strange artifacts but it has no influence on the illumination.

Are the displays supposed to cast any visible illumination?

Yes, absolutely. If I compare it to some real equipment I have here, then a display with a similar brightness, light and background color, at least illuminates it's frames and close objects clearly visible.
So for example the inner frame of the big display and the knobs and buttons next to the small diplays and the walls of the case close to a display or an LED row should receive clearly visible illumination.
In reality it's not just a little but really makes these other objects visible in a dark room.

But in the last image you posted, I would expect some illumination on the knobs around the displays. What kind of material do you have on the knobs?

Me too. All materials that should receive illumination like knobs, case and display frames are glossy materials with roughness and specular values between 0.2 and 0.4.

Actually I can get the light sources to illuminate other objects, but then the light source itself has to be that bright, that all the displays and LEDs appear bright white.
That's not what I observe when I look at similar real world objects in my office.

[bepeg4d]

Hi,
here is my attempt without emitter behind the glass, I have used a specular with sss and emission active. I have used also a dirt node in the transmission node but you can use a map for simulating the different illumination in the plane.

ciao beppe

[friscokid]

Hi Beppe,

thanks a lot for the renders and the suggestion. The illumination in your renders is close to what I'd like to achieve.
However, when I try the same setup as you did, it just doesn't work.

Image 1 is a render with no emitter in the back of the display but with an emitter in the scattering node of the glass material.
I suppose this is the same setup that you've been using too.
Unfortunately, as you can see, there is almost no illumination of other objects even though the emitter is much brighter than the one you were using.

Image 1

Image 2 is the material setup of the glass pane with emission in the scattering node. Please let me know if this setup isn't correct.

Image 2

Image 3 is what I actually want the display to look like, except that here the illumination of other objects is completely missing.
In this version I placed an emitter in the back of the display and the glass pane is just a specular material without emission.

Image 3

Image 4 is a photo of a display that looks the way I want the displays in my render to look like. Even though the light in the back is not too bright, it clearly illuminates the frame and the outer object.
Unfortunately I'm not able too create the same effect.

Image 4

Do you have any idea why the emission in the scattering node of your glass material is illuminating the other objects in your render, but when I'm using the same setup, it just doesn't work?
Thanks

Jan