IES shape does not render correctly

[k_18]

Hi, here is our issue: When we create an IES light and load an IES profile from any vendor (eg., zumtobel tecton lamps), the light distribution (from a single point in space) does seem to change and so does the gizmo in the viewport (a 1500mm light does indeed seem to alter the gizmo's shape to reflect that length). The shape of the distribution when rendering, however, does not seem to pick up that length and the light seems to all be emitted from a singular point in space.

When comparing the results we are getting in DIALUX for example, that seems to support the issue as the distribution cone on a test scene looks significantly different in the sense, that it does indeed stretch across the full length of the light as one would expect. Now I assume we do something wrong, but have no idea what that would be, given the limited number of options in the light shader. Any help on this? We do need the VRay IES light to pick up on the actual product's length correctly on our current project.

Thanks in advance,
J

[k_18]

To further elaborate on this: Whatever we change in the IES light's Shape section does not have any effect on the distribution whatsoever - whether it is set to spherical, 'take from IES profile', 'rectangular' or altering the width, length or height etc. manually - it all renders identical in the sense that the profile's light distribution always seems to be emitted from a single point. I suspect the light shader is broken at this stage but would love to hear I am doing something wrong here.

[k_18]

One more thing: It does seem (!) to render correctly when we take the scale values from the 'From IES file' section in VRay's Light Shader (which do display the correct scale of the light), then set them all to a value of 1 in the light Shader and instead scale the actual gizmo through Maya's scale values. Hmmm.... Can someone confirm this?

[k_18]

If anyone from Chaos could please elaborate on this that would be great. As far as we can see the IES light does not give correct results and we will need to shift to dialux if this is no user error on our part.
Thanks, J

[hermit.crab]

To further elaborate on this: Whatever we change in the IES light's Shape section does not have any effect on the distribution whatsoever - whether it is set to spherical, 'take from IES profile', 'rectangular' or altering the width, length or height etc. manually - it all renders identical in the sense that the profile's light distribution always seems to be emitted from a single point. I suspect the light shader is broken at this stage but would love to hear I am doing something wrong here.

The Light Shape option is meant to override the Soft Shadows. I don't think it's supposed to change the actual distribution shape (it changes it for the soft shadows only).

One more thing: It does seem (!) to render correctly when we take the scale values from the 'From IES file' section in VRay's Light Shader (which do display the correct scale of the light), then set them all to a value of 1 in the light Shader and instead scale the actual gizmo through Maya's scale values. Hmmm.... Can someone confirm this?

Manually scaling lights is never a good idea.

[k_18]

Hi Aleksandar, I agree, never a good idea - but then again it simply does not render correctly as is. Did you manage reproduce the issue? As such it simply does not render whatever profile is loaded correctly

[k_18]

This render is from VRay with the IES light and a Zumtobl profile loaded. No scaling on the gizmo, the light's emission should be taken from the IES profile - and VRay correctly lists the actual shape of the emitting surface in the Shape section, so the information is correctly embedded in the respective IES profile.



While it looks as if it does take the light distribution into account, it totally neglects the actual shape of the emitting surface - because the light is actually a stripe light and the distribution should look like this (taken from Dialux, same IES profile):


So unless we are doing something completely wrong, the IES light does not work correctly and is unusable in its current form.

[hermit.crab]

I understood. So currently the only way to get an emission shape other than a point is to scale the light, which as already mentioned is not a great idea. Maybe we should consider the Light shape parameter to affect the emission along with the soft shadows as well. I'll mention the case to the project manager.

[k_18]

Maybe we should consider the Light shape parameter to affect the emission along with the soft shadows as well. I'll mention the case to the project manager.

I am confused - so if I understand your reply correctly the VRay IES light does not support light emission as per the supplied IES profile? That renders the whole point of the light shader rather useless unless you use point lights, I reckon. Could you please clarify if I got this right? That would rule out 90% of all IES light profiles available out there

[hermit.crab]

Yes, you got it right. We'll see what we can do for future builds.

[k_18]

Ugs, that is a rough one. So basically IES lights are not supported as is. Ok, at least we know we need to switch engines for this job. Thx for the heads up

[burkhard_wand]

Hi there, I have a similar problem:

I can't target a asymmetric IES light. I tried several asymmetric files (bollard light) to fit along a curvy path. There doesn't seem to be a way to do this?

This is not a problem with symmetrical light distribution. I found out in a help topic that it is possible to "toggle selectively" in 3D Max, but I couldn't find this option in Rhino.

Does anyone have an idea how to solve my problem? Kind regards, Burkhard