When the light leaked

a few days ago when my wife had a shower (no, stop your naughty thoughts right there) i saw some light coming out of the bathroom door which was left open a little gap, while the rest of the house was dark showing me an array of light beams on the floor. as a part time professional and artistic photographer i am always intrigued by light play, shadow play and any physical artefacts thereof.

since i am still in Cycles test mode it was a perfect excuse to quickly rebuild that in Rhino. figuring out what actually caused the effect led me rethink and to experiment with the set up and accidentally found out that Cycles seems to be based on some kind of physical additive light system. probably normal but i did not test that in any other application yet and happily surprised by the result i thought i share it with you.


Cycles is not a spectral rendering engine. Caustic effects are not very natural to Cycles.

How did you create the rainbow effect?

I meant the actual material and light setup (: But thanks for the link!

the answer is all in the above and easier as it seems. i am sure you figure it out soon. i dont want to give away this little riddle too fast :slight_smile: since it was nice getting there with a surprise.

must have been something like this camera obskura setup, right?
The remarkable thing to me is, that its mirrored like in real world.

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interesting, i think this effect is a based off of its geometry at which angle the light beams enter which leads to this natural result in 3d of turning up side down and left to right.

and to some degree you are not far from the truth!

Ah yes of course, silly me. I had my brain turned off, clearly.


glad your cracked it :slight_smile: i hope you had some fun. also how long did you render it? mine took forever, i also wanted to pump up the volume on the emission a bit to get a clearer image but man does it take long on my machine :neutral_face: so i avoided trying again due to lack of time

rendering 5 minutes and its still grainy as hell i mean

alright Nathan, found some time and thought i give it another go. also i figured that when the render is not in foreground or hidden, at least on mac, it keeps elapsing the time but does not render further and therefore renders much longer. a test with the same render set up with 500 path tracing samples revealed that one time it needed 30 minutes when it was mostly in the background and one time when i suspected this happening keeping it in foreground basically watching, it was done in 4-5 minutes

and will never be?

@goozoon it would be better to quote the section you are referring to. scrutinizing the entire topic trying to find out what you are talking about is not always as easy as here…

nevermind :slight_smile:

me too would like some caustics in cycles. there have been approaches but i am not sure what their status is, it has been a while since i researched this topic. and if any of these will make it into cycles at all and how @nathanletwory will handle it.

maybe nathan has something refreshing to add.

There is an on-going effort of creating a spectral version of Cycles. Not sure what its current status is, I haven’t checked in about half a year.

Once that is stable I believe the people working on it were going to add different caustic effects.

I don’t know if they are planning to propose a patch for this into upstream Cycles.

But there are engines available for Rhino that do know how to do good caustics and other techniques that Cycles doesn’t.

FYI the small arrow in the reply will open the post being replied to

in case didn’t know yet

ups… nope didnt know. thanks!

if there would be any update regarding caustics, would it then rather be in Cycles X ?

As far as I know no new features per se have been planned yet. Cycles X is a reachitecture of Cycles, going for feature parity with old Cycles, and at most adding some new backends (HIP, maybe others).

But if any new features like caustics would be worked on it will definitely happen after Cycles X is in, so essentially in Cycles X codebase, not pre-Cycles X :slight_smile:

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Can the slower members of the community have a less cryptic hint?

I was sure it was about the colour of the lights but apparently I was terribly wrong

hi @Artstep as far as i can tell you seem to be on the right track, the image you are showing was what i initially saw and triggered my motivation to rebuild it from scratch, it is basically just on step away. but to clarify, what exactly do you mean by colour of the lights?


What you are seeing there is a [redacted]. I tried various ways of reflecting light and playing with falloff settings, but it seems everything stays white - I did notice not all lights are created equal in terms of producing colour, this is with point lights if that’s the mistake?

Probably missing something pretty obvious here, sorry :sweat_smile:

You most likely have your ground plane set to shadows-only.

Set it to have the default material to get coloured light on it.


it appears you have cracked it either :slight_smile: from what i remember is that changing the color of the groundplane to default helps.

right, nathan was just a second faster.