light area not visible in reflections when using IES lights

[mp5gosu]

See here:
The area of IES lights become invisible to reflections. I'd assume, they stay visible.
Thje first image shows the scene setup. It's a plane with 100% reflective glossy material.
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Full-speed non-debug version
Build timestamp: Oct 31 2018 17:14:41
Version: B2 (core 3)
Cinema version: CINEMA 4D Studio R19.068 S
Plugin status: initialized successfully

[TomG]

It depends on how wide or narrow the IES is, as to whether it reflects or not. So it would seem to be similar to the Prevent Black Appearance for the direct visibility (that is, since the IES is narrowing the directionality of the light, it may be so narrowed it doesn't show up in reflections).

Interestingly, it can show up in reflections of reflections even when that first reflection doesn't show up to the camera (presumably due to how the angles all inter-relate - scene attached but you'll need to add your own IES, I was using the ones that come with the Corona install).

I can't say if this is physically correct, expected, or a bug at the moment. A workaround in any case would be to have two light sources, one to cast the light, one to show up in reflections.

[TomG]

The same thing happens in Max, so it looks like a limitation (or something that is physically accurate even)

[mp5gosu]

Hey Tom,

thanks for your efforts. I was actually also thinking about all points you mentioned before I created this topic, but a simple fact cannot be ignored: If it is visible directly, it must also be visible in single-bounce reflections unless explicitly excluded... So I'd also assume it's a limitation or bug. We're using area light dummies of course.

However, it is tidy and a working IES reflection would become useful. ;)

[TomG]

I believe it is that "Prevent Black Appearance" is only for direct visibility from the camera angle, and that the prevent black appearance doesn't have an effect on the angle from the reflecting surface. I believe that's a limitation at present (devs can correct me if I am wrong :) ), in that the prevent black appearance is only taken into account for the camera view and not reflected views (so that a narrow angle of IES would mean no light from the light source reaches the surface it would be reflecting on, and so no reflection). We'll see what future plans are in this regard!

[mp5gosu]

Ah, that sounds plasubile to me! Thanks for that hint. With this, I can at least tell my colleagues some kind of reason why this happens. ;)