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Primitives that emit light no longer work as expected when their opacity is set below 1.0

GrendelbertGrendelbert Posts: 31
in The Commons

For years now, I've used primitives like spheres as part of my lighting in Daz. I set the emission values I want and then set the object itself down to 0.0001 opacity so that it's invisible. Doing this gets around the trouble with using spotlights (such as even with Render Emitter off, it still reflects). Using primitives as emitters like this worked for me until just the other day. Now, the primitive only emits light equal to its opacity setting. At 0.0001 there's no light being emitted at all. When I set the object opacity higher, I get some light, but the object itself becomes visible, which obviates the whole point of using this method for lighting, i.e., to hav a completely invisible light source that doesn't reflect on shiny surfaces.

I have 4.20.0.2 installed. I haven't changed anything. I went back to older scenes where I've used this method and found that they no longer work that way either.

What in the world happened?

Comments

  • zombietaggerungzombietaggerung Posts: 3,756

    Iray/NVIDIA changed how that works. There's some more discussion of this here: https://www.daz3d.com/forums/discussion/551301/ghost-lights-what-s-happening-and-what-s-next

  • GrendelbertGrendelbert Posts: 31

    Aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaarrrrrrrrrrrrrrrrggggggggggghhhhhhhhhhhh!!!!!!!!

    Thanks, zombietaggerung. It seems the fix is to up the KCD luminence for emissions way, way, way, way up on a scale of what was once 100 kcd = 1000000000 kcd.

    I hope the Iray/NVIDIA change does some incredibly mindblowing things in compensation for removing ghost lighting from our toolkits (or at least for making using it exceedingly fussy), but I suspect it won't.

    Isn't there an old engineer's maxim about not fixing what ain't broke? Fixing what ain't broke is how you break things.

  • Charlie JudgeCharlie Judge Posts: 12,868

    Grendelbert said:

    Aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaarrrrrrrrrrrrrrrrggggggggggghhhhhhhhhhhh!!!!!!!!

    Thanks, zombietaggerung. It seems the fix is to up the KCD luminence for emissions way, way, way, way up on a scale of what was once 100 kcd = 1000000000 kcd.

    I hope the Iray/NVIDIA change does some incredibly mindblowing things in compensation for removing ghost lighting from our toolkits (or at least for making using it exceedingly fussy), but I suspect it won't.

    Isn't there an old engineer's maxim about not fixing what ain't broke? Fixing what ain't broke is how you break things.

    There is a free  script that may help fix the problem:

     https://www.daz3d.com/forums/discussion/548061/iray-ghost-light-fix-dse-for-daz-studio-4-20-o-later/p1

  • GrendelbertGrendelbert Posts: 31

    Ack. That's not a fix after all. I get fireflies where the ghost sphere is, no matter how low I set the opacity.

  • Charlie JudgeCharlie Judge Posts: 12,868

    Did you try the free script I linked to above?

  • GrendelbertGrendelbert Posts: 31

    I haven't tried it yet. I was hoping that increasing the luminance would resolve the issue with my primitives. I have found that the Iray Ghost Lights Kit (https://www.daz3d.com/iray-ghost-light-kit-one) does what I've been doing and is newly releasedto work with Daz 4.20.

  • GatorGator Posts: 1,312

    Yeah, I've been meaning to put in a ticket... it messed up scenes like The Red Crow Inn, which basically uses ghost lights for the candles.  I bought the KA's new ghost light set and tried copying those surface settings, mostly works but they leave weird artifacts similar to fireflies.

  • Matt_CastleMatt_Castle Posts: 2,647

    Grendelbert said:

    Isn't there an old engineer's maxim about not fixing what ain't broke? Fixing what ain't broke is how you break things.

    From Nvidia's perspective, this was broken. Iray intends to be a realistic renderer, and light magically appearing out of nowhere isn't actually possible, so opacity not influencing light emission was an unintended effect.

    ... albeit an extremely useful one that was being widely exploited.

    However, note that the "Iray Visible to Primary Rays" advanced functionality is now a thing, and is supposed to help smooth over this change. It functions the same as Render Emitter for lights, really... which, while you need to combine it with the opacity and boosted luminance values to hide it in reflections, will stop you getting fireflies off the primary source (at least as long as nothing else is in the way, like a window, at which point it's no longer a primary ray).

    It's also a very useful function for tricks like letting the camera see in through walls without it completely changing the lighting.

  • karlsfriend_f7ccaca9e2karlsfriend_f7ccaca9e2 Posts: 73

    I ended up re-installing Daz 4.16.  I've got too many set-ups that I've created over the years to go back and rework them if I decide to go back to one.  I don't see how this is an iray thing when it still works in the older versions.  What did Daz do on the back end?

  • PerttiAPerttiA Posts: 10,024

    karlsfriend_f7ccaca9e2 said:

    I ended up re-installing Daz 4.16.  I've got too many set-ups that I've created over the years to go back and rework them if I decide to go back to one.  I don't see how this is an iray thing when it still works in the older versions.  What did Daz do on the back end?

    DS 4.16 has an older version of Iray, one that has not been fixed by Nvidia. 

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