Had run into some troubles using lighmix + Light emitting materials - not sure if those are a bugs, some combination of those + some intended behavior or some stranginess in the way I work + I cannot think of how to put it on mantis separately as those 3 are somewhat related (or at least in this particular case) and wouldn't make such an impact if described one at a time so here goes:
1) Corona lighmix LightSelect ignores all the materials\objects containing CoronaLightMtl with Emit Light ticked off both in manual and automatic creation modes. Same goes for the regular CoronaMtl with some Self Illumination but that is not the problem cause i don't know who in their right mind uses those.
It is quite senseless, especially in case of grouped lamp fixture models which containin, say, some light bulbs or even some filaments within those bulbs which contain such non emiting materials and Corona or standard light objects for the actual lighting itself, all of which, logically, should be controlled by\contained in the same light select element to make brightness adjustments\dimming of that lightSelect pass for the that whole lamp model at the same time. Because of this behavior, those light bulbs\filaments cannot be dimmed with the rest of the lamp fixture using the same element's slider and it's quite easy to guess the rest, speaking of which - the Rest(unassigned) lightmix element does pick them up automatically but that's surely not the most convenient way to control those I think.
2) CoronaRaySwithMtl does not respect the Emit Light tick on\off in CoronaLightMtl if that material is put into Global illumination override slot - it presumes what it is always ON, on top of that if it is off it produces light but those material's emitted light\gi is sampled in a very weird way and i mean really WIERD way - it's easily reproducible so you can see what I mean.
This can lead to some unexpected and quite nasty behavior in some cases - yesterday, I've spent almost half a day trying to figure out where that nasty, unexpected and unyielding noise is coming from in my currently worked on scene and in the end I've found this to be responsible for it.
3) CoronaRaySwithMtl and CoronaLightMtl again. When Emit light is ticked ON inside the instanced CoronaLightMtls which are put in all the slots except Global illumination, which in turn contains no light emitting material or left empty, the whole CoronaRaySwithMtl renders black, same goes for Self Illumination containing regular CoronaMtls. Not sure if that's a bug or an intended behavior but it surely doesn't make too much sense to me, especially in a regular Self illumination containing CoronaMtl's case - I don't use the latter, though but it can be still encountered due to some quick conversion from vray made models whether one wants to use it or not. Still that bug\behavior wouldn't bother me at all if not for combination of (1)+(2)
4) or partially more like extension of 1+2+3. Well, I thought, and it seemed pretty logical to me at the time, what as a temporary solution to battle (1), I could use CoronaRaySwithMtl containing instanced CoronaLightMtl with Emit light ticked ON in all slots except Global illumination slot, leaving it empty or with some non emitting material to battle (2) along the way - it should allow LightSelect element's "+" function to be able to pick those objects\materials. Well, it does help, at least with the picking\adding to lightselect element part, except the material itself renders black due to the (3) so in the end it does not help at all.
So to wrap things up or why it bothers me so much - partially I described it in (1) all I can add to that is what having light emitting light bulbs not to say light emitting filaments inside the glass bulbs is a most sure way to make one's renders longer, waay longer + it can lead to some various but all nasty artefacts if the geometry of those bulbs\filaments is not perfect - which is often the case with too much of 3rd party 3d models nowadays (
Thus, the most important for me would be the fix for (1) and if that can be fixed all others are less important. If for some reason (1) cannot be fixed when fixing either (2) or (3) or even better both of them should do the trick. And, of course, it would be best if you could fix them all, for the greatness of Corona, of common sense and for all which is good in the world ))
