Splotchy light effect in renderings

[Tom W.]

Does anyone have any advice as to how to deal with the splotchy light effect I’m getting in these renders? I have tried various different Render Modes + the only one where the splotchiness doesn’t appear is Final Quality Renderworks (middle left). The top two renders use my own RW Styles which I employ regularly + never normally have any issues with. The remaining three renders use various other RW Styles.

 

 

I have tried reducing the brightness of the Light objects (they are Point Lights), reducing the number of Lights + removing Reflectivity from the textures used on the lamp shades but none of this has any effect on the splotchiness. The only thing that gets rid of the splotchiness is changing the Falloff from Realistic to Smooth:

 

 

It's a bit hard to tell from the low DPI renders above but the negative effect of this is that it reduces the quality/realism of the scene but perhaps that's the compromise I have to make to get rid of the splotchiness?

 

As a comparison this is the same scene but using Spot Lights + here there were no problems whatsoever, I just reduced the brightness of the Lights + to me it renders very well:

 

 

I’m just interested to know what’s going on: why changing from Spot Lights to Point Lights is causing so many problems.

 

What role Realistic Falloff is playing in creating the splotchiness.

 

What is particular about Final Quality Renderworks that means it’s not affected by the splotchiness whereas all the other RW Styles are.

 

Any other settings to try messing with.

 

I have come across splotchiness before in relation to Glow Reflectivity being set too bright but there is no Glow here.

 

Should I try Spot Lights instead of Point Lights in my pendants?

 

Any guidance gratefully received! @Luis M Ruiz?

 

Thanks.

[markdd]

One thing I have noticed is that this effect is more noticeable when a light object is in Realistic falloff and is in very close proximity to other geometry. Using Spots as opposed to Point lights would support this.

 

If you were to keep the Lights but remove the geometry (by turning off the geometry class) do you still see this effect? The tests that I have done over the last few years show much better results when the geometry is removed. Obviously not entirely helpful, but it will at least illustrate the point.
 

Another option that I have tried is to change the texture of the geometry that contains the light to have no effect at all. You can do this by changing the indirect lighting options of the texture and remove Emit and Receive light. You can also change the Cast shadows function to off.

 

Up the bounces as well to 16. That should help quite a bit. 

 

Just some thoughts…..

Edited February 6, 2022 by markdd

[Tom W.]

Many thanks @markdd this is extremely helpful.

 

My Point Light was part of a GLS light bulb symbol (i.e. inside the bulb geometry) + the bulb symbol was in turn located high up inside the symbol for the metal lamp shade (as the bulb would be in reality) so all in all the Lights were fairly encased in geometry.

 

So I moved the Light downwards, out of the light bulb, to a position a couple of inches below the lamp shade.

 

And I edited the texture used on the inside of the lamp shade + the texture on the light bulb symbol + disabled Emit/Receive Light + Cast/Receive Shadows in both cases.

 

And I reduced the brightness of the Lights to 55%.

 

The bounces were already set to 16. 

 

At 24dpi the viewport looked great but unfortunately I realised when I rendered at 300dpi that I still had some small splotchy patches of light on top of the skirtings. But by disabling Emit Light setting for the texture used there I was FINALLY left with a splotch-free rendering:

 

 

Wow what a lot of work to produce a fairly straightforward image but it's been a good exercise + I wouldn't have managed without your help so thanks again. Every day you learn something new...

[markdd]

Glad that has helped. 

[Andy Broomell]

On 2/6/2022 at 3:15 AM, markdd said:

One thing I have noticed is that this effect is more noticeable when a light object is in Realistic falloff and is in very close proximity to other geometry.

 

My recent experience also found this to be the culprit. I had a Point light within a fixture similar to the one above. When I switched from Realistic to Smooth the splotches went away 🤷‍♂️

[grant_PD]

Realistic/Smooth refers to the falloff of the light energy.  Linear falls off in a straight line: the further away you go the less bright the light.  Realistic uses a curve (inverse square) to approximate a real world falloff.  It could be that what you are seeing is the lack of available energy from the lights where they get splotchy, hence the renderer has competing samples (one very dark sample next to one very light sample) which results in the splotches.  With the linear falloff there is enough available energy to have good sampling and so the render is smoother.  I could be completely wrong, just a guess.  

 

Sometimes I feel like we have too many expectations of these programs to understand what we inherently intuit from the real world....

[Luis M Ruiz]

On 2/6/2022 at 5:53 AM, Tom W. said:

Should I try Spot Lights instead of Point Lights in my pendants?

 

Any guidance gratefully received! @Luis M Ruiz?

 

Hello Tom.
In this particular challenge, yes, make use of spotlights and adjust some of the settings. The spread angle, set the spotlight to realistic and add color temperature. Do not place the light so close or touching a surface.  I think I'd set the scene with custom renderworks, ambient light to 10%, four bounces and very little occlusion.

 

[Mark Aceto]

24 minutes ago, Luis M Ruiz said:

The spread angle

 

Reiterating this. I ratchet up the spread angle for a softer focus. In the screenshot below, the light on the left is set to the default 60/30, and the light on the right is set to 90/30. Both are set to Soft shadows, Smooth falloff, 600 brightness This technique can be a bit biased (faked) but it works, and is predictable.

 

 

Although it doesn't sound like a solution to the issue that you've already solved, I would caution against increasing the number of bounces in such a small room. I've had issues where I was scratching my head trying to figure out why the West wall looked so weird, and it turned out to be light bouncing off the East wall. That's not a hard and fast rule but definitely one of the first settings I'd check when troubleshooting unexpected results.

 

Also, Point lights seem like a good idea to bump up the GI but that approach can be frustrating, so the built in Indirect Lighting options serve me better. And I'm huge fan of AO (a little bias goes a long way).

[Tom W.]

Thank you @Mark Aceto + @Luis M Ruiz for your advice + suggestions, and indeed to everyone else who’s commented: it’s been a really helpful + interesting discussion (thank me for not saying ‘illuminating’ 🙂). 

 

I did try 4 bounces originally + it didn’t make any difference: in the original post, the top left VP is 16 bounces + top right is 4. I suppose the splotchiness is slightly less in the 4 bounce version…

 

But I will play around with a wide-spread Spot Light instead of the Point Light + see how that compares. I wonder whether this will allow Emit/Receive Light + Cast/Receive Shadows to be re-enabled for those textures I turned it off for...

 

Thanks

[Tom W.]

Ok here's the version of the same VP but using Spot Lights instead of Point Lights. I'm quite happy with this. The light isn't being cast onto the walls in quite as natural a way as it was in the Point Light version above but I was able to achieve it without having to edit all the textures: in this version all the textures have Emit/Receive Light + Cast/Receive Shadows re-enabled.

 

 

The RW Style I used has 4 bounces, 10% Ambient Lighting + 15%x300 AO. The Spot Light has 150° spread + 60° beam.

 

I changed the texture inside the lamp shade to 100% Glow in order for that to be illuminated (which happened by default using a Point Light).

 

The only other small loss is that no light is thrown out of the square holes in the top of the shade as was the case with a Point Light - and would happen in reality - which I quite liked seeing in the first render.

 

 

One question: if I've enabled 'Use Emitter' I have a 'Brightness Value' parameter + a 'Dimmer (%)' parameter. What difference does it make, if I'm wanting to increase a Light's brightness, if I use one setting over the other?

 

Thanks again for all the tips. If I get the splotchiness again I now know two ways to get around it without having to turn off Realistic Falloff.

[Luis M Ruiz]

To start, I'd use brightness by percentage. 100-150-200%. all of these values really make a difference when using normal, smooth or realistic setting. When it gets interesting is when you make that light as a symbol. The symbol can also be control by percentage.  So you could have a standard light at 100% brightness inside the symbol but when placed in your model set at only 50%. 

[Tom W.]

23 minutes ago, Luis M Ruiz said:

When it gets interesting is when you make that light as a symbol. The symbol can also be control by percentage.  So you could have a standard light at 100% brightness inside the symbol but when placed in your model set at only 50%. 

 

I only realised this recently: has it been around for a while? I see it works with symbols within symbols... so if you have a Light object within a symbol that's within a symbol that's within a symbol, you can control the brightness of that much-buried nested Light object by the brightness setting on the container symbol...?

 

I'm still not 100% sure the difference between the two brightness controls:

[Dave Donley]

@Tom W. The brightness value in your screenshot is like max brightness of the bulb and then the dimmer is an additional control like a dimmer slider.  Same for lights in symbols, the additional control shows for symbols that have lights inside and this is a dimmer/multiplication factor on the light brightness inside.

 

[Tom W.]

@Dave Donley thank you ok so basically set the 'Brightness Value' to however many Lumens you are thinking the lamp would have in reality then leave it at that + if necessary use the 'Dimmer (%)' setting to tweak it up or down if the rendering requires it? I think I immediately went to the 'Brightness Value' + started increasing that because in a non-emitter Light the setting is called 'Brightness' too. But in fact I would have been better to leave the Brightness Value as it was + use the Dimmer setting to up the brightness. Ok I will remember that from now on thank you!

[Mark Aceto]

Also, making the choice to use Emitters enables more Lighting Options settings if that's something you're interested in (or ever wondered about):

 

[Tom W.]

5 minutes ago, Mark Aceto said:

Also, making the choice to use Emitters enables more Lighting Options settings if that's something you're interested in (or ever wondered about):

 

 

Ok I was vaguely aware of this but had forgotten thank you. So this provides another way of raising or lowering the brightness of the Lights in a rendering: so you might have a light fitting that contains four individual Light objects who brightness you can control individually within the symbol; then the overall combined brightness of the symbol can be increased or decreased using the Brightness setting for the symbol; then if you had four different but similarly put together symbols in the scene you could raise or lower the overall brightness of all of those symbols at once using the 'Emitter Brightness' settings for the RW Style???

[Mark Aceto]

6 minutes ago, Tom W. said:

if you had four different but similarly put together symbols in the scene you could raise or lower the overall brightness of all of those symbols at once using the 'Emitter Brightness' settings for the RW Style???

 

I'm not sure (which is why I generally don't use Emitters). It won't override the percentages you set for each light's properties.

 

My (very bad) understanding of how this works is that you can adjust the GI color temp with these settings if you chose to use emitters but honestly none of it makes sense to me.

 

Dave and Luis, how does this work?

[markdd]

This setting adjusts all Lights that have been set to emitters en masse. All the levels are set relative to each other.  (this includes custom lights as well). 

 

Regular Light Objects are not affected by this setting. They take their percentage from the white value of the monitor. ie 100% of a white source will give you pure white. Lower levels will be a grey-scale down to zero (black). Higher than 100% means that the light will start clipping. This all changes quite a bit when you start to set things up using a smooth or realistic falloff, but that is the priciple at least. 

 

Realistic falloff uses the inverse square rule which is how light falls away in the real world.

 

Hope that helps a bit!

[Tom W.]

I understand the white color temp setting: that is I think calibrating the baseline temp all the other emitter temps are measured against.

But I hadn't really took on board what the emitter brightness setting did. I guess again it's technically calibrating the brightness the individual emitters are measured against but in effect allows you to raise or lower their brightness en masse...

 

Posted before saw Markdd's explanation!

Edited February 10, 2022 by Tom W.

[Dave Donley]

Yes en masse.  This setting pre-dates the Renderworks Camera object which connects the lighting parameters front end to a calibrated virtual camera back end.  The render options used to be the only convenient way to relate the overall rendering brightness with physically-based lights.

 

If you use Renderworks Cameras then you can turn on exposure to adjust the brightness of the scene as a whole, instead of changing the light object's brightness values either individually or en masse.

 

[Mark Aceto]

So if I’m to understand this correctly, the settings in each lights properties won’t change (literally the values entered in each field), so those settings will be overridden?

[Dave Donley]

If you are asking about using the camera the light values are not changed at all, the response of the virtual film in the simulated virtual camera determines the brightness shown in the rendered image instead of changing the light brightnesses at the input.  So the output is adjusted instead of adjusting the inputs.

 

[Mark Aceto]

I'm just confused because changing the settings here:

Does not change the settings here:

[markdd]

Its a global setting that adjusts all the Custom/emitter Lights together relative to each other. It is a very useful way of balancing known sources from say custom .ies files and other emitters with the basic Light objects which don't relate to real world values at all.

 

All the Custom lights and emitters in your example will become 4.2 times brighter.

 

 

Edited February 11, 2022 by markdd

[Jesse Cogswell]

@Tom W. The Brightness Value is a way to calibrate the actual intensity of the light source to match objective reality.  I use it all the time to produce realistic renderings using theatrical lighting fixtures and museum track heads.  In these types of applications, all lighting fixtures of the same model (such as an ETC Source 4) generally use the same lighting source, generating the same overall lumen output.  However, we use a series of either lenses or reflectors to change the concentration of that initial output.  For example, the aforementioned Source 4 has a range of lensing options between 5 degrees and 90 degrees.  A 19 degree lens is going to make the light small, but relatively bright while a 50 degree lens will make the light very wide, but much dimmer.  Both of these would have the same lumen output since they use the same lamp source.  So instead, we use something called center beam candle power (CBCP), otherwise known as peak candela (PC), which is measured at the center of the beam of a directional source.  This value is then used to calculate footcandles (one lumen per square foot) or lux (one lumen per square meter) using the inverse-square law (which is also what is used in the Realistic falloff mode).

 

Practical example:

    ETC Source 4 19degree w/ HPL 575 lamp - 16,520 lumens with a CPCP of 236000

    ETC Source 4 50degree w/ HPL 575 lamp - 16,520 lumens with a CPCP of 32000

 

    With a throw distance of 20', the 19deg will have an intensity of 590 footcandles (236000 / 20²) while the 50deg will have an intensity of just 80 footcandles.

 

So, here's how all of that relates back to Brightness Value.  By default, when you take these two lights and put them at 100% intensity without having the Use Emitter setting ticked or having the Brightness Value calibrated properly, they will appear to be the same (seemingly arbitrary) intensity, which is obviously not true to life as reflected in the above example.  In this case, I set the Brightness Unit to Candela and the Brightness Value to match the specific fixture.  This is especially important in doing museum lighting, where I might be restricted to one-circuit track where all of the track heads have to be at the same dimmer intensity, but may have different beam degrees and therefore different outputs.

 

In your example above with a standard pendant fixture, you would have the Brightness Unit set to Lumens (since the light isn't being focused in any meaningful way, you can get away without using CBCP) and match the value depending on the lamp specification.  You could even use this to do a side-by-side comparison of, say, a 40w equivalent LED A-Lamp versus a 60w equivalent LED A-Lamp set to the same dimmer intensity.

 

This may have been a lot of information, but hopefully it will help you in setting these values to get the output you are looking for.