Light source in lighting fixture cast shadow

[Anonymous]

I have a strange problem.

Using rectangular light source with IES file creates shadows in rendering even tough the light source should not have any effect on the rendering. How to avoid light source influencing a rendering?

I have tried turning light source off in VG but no difference

I am running Revit 2018.

In the family shown I have moved the light source in the lighting fixture away form the fixture itself to illustrate the problem.

Photometric setting shown at the last picture.

[barthbradley]

Almost sounds like you are describing an effect produced by a material that has a Self-Illumination Property (untickable).   Post the file.  

[barthbradley]

Yep, that's what it was. The material assigned to the geometry of the light has "Self-Illumination" checked (under Appearance tab).  Uncheck it.  

[barthbradley]

FWIW: Your Light Family is peculiar to me. The Light Source in it is not positioned directly under the housing. Is this intentional?  

[Anonymous · Accepted solution]

Hi Barthbradley

Thanks for your reply and ideas for a solution.

Turning self illumination off has no effect.

Turning light source off in visibility graphics for the view has no effect. (if I turn off Lighting Fixture in VG lighting fixture are not rendered - off cause!)

It was by intention that I moved the light source away from the lighting fixture to clearly illustrate the problem.

I have testet different settings and found that it is the IES file used for this lighting fixture that causes the problem. And importantly to note it affects other lighting as well - meaning that all light sources from different lighting fixtures cast shadows even thoug they work just fine if used alone. When changing the IES file all light sources act as expected.

IES seems to be a bit tricky to use. Even slightly inaccuracy seems to have great impact.

Once again thanks for your time on this issue.

[barthbradley]

Are you saying that you have NO like issues if you use a different ies file.  Strange.  

Well, all I can say is that I have no issues with your file - or your ies file.  They behave correctly for me. 

[barthbradley]

Before you pat yourself on the back, you ought to post your IES File for others to test.  Like I said: I HAVE NO ISSUES WITH YOUR IES FILE.  I would be very curious to know the real issue/solution.    

[barthbradley]

If you are taking what is shown in this screenshot; this is correct behavior. In fact, it's well-documented. IES Light Shape does not display in Realistic Mode. Only the Emit Shape displays in Realistic Mode with "Light Source" Subcategory turned on.  

Again; the reason the Emit Shape is not positioned at the light fixture housing geometry is because you offset the Light Source in the Family - as I explained and pictured above.  

[barthbradley]

If you don't believe me, just test yourself.  Easy enough to do.   Here's the exact same results with the OOTB Revit "Downlight - Strip" which uses a different Photometric Web File (3 are visible in this view). The Light Source has been offset from the housing geometry in the Family and the Emit Shape changed to Rectangle for this test.

  

[barthbradley]

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@Anonymous wrote:

I have testet different settings and found that it is the IES file used for this lighting fixture that causes the problem. And importantly to note it affects other lighting as well - meaning that all light sources from different lighting fixtures cast shadows even thoug they work just fine if used alone. When changing the IES file all light sources act as expected.

IES seems to be a bit tricky to use. Even slightly inaccuracy seems to have great impact.

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You must be a Lighting Engineer or Scientist. I am not.  But, I can't imagine how a simple Text file that produces this unamazing and rather boring geometric shape could possibly be problematic.  

I'd love to see a problematic IES file, if you got one you can post.  Thanking you in advance.  

[barthbradley]

FWIW: if anybody is interested in testing, I've attached the IES and RFA which I found here:

https://www.bimobject.com/en-us/solar/product/solarlight_ray

@Anonymous : Still can't replicate your issue - and I tried my darndest.  Could be related to something else entirely, like maybe Materials or Rendering Settings.  Could be hardware-related as well.   

[Anonymous]

Hi again

You are right. After posting that it seemed like the IES giving problems I testet furter and found that it was a combination of a different IES and moving the light source downward that seemed to have a positive effect.

Just to clearify the issue - when rendering I get theses "shadows" at the ceiling which comes from the light source inside the Light fixture family. Attached is the IES files I use.

I have testet in Revit 2020 with same result.

I render in HIGH quality - Dont you get these shadows if you open the file rotat to look upward at the ceiling an render in high? what Revit version are you running?

[Anonymous]

Tested the IES once again.

In my file there is two IES-files. I tried to set the same IES on both family types.

365....ies seems to cast a bit of light upwards which is right according to the ies file data.

b5c....ies only cast a shadow on the ceiling.

1x4...ies is an ies file included in the Revit installation and this gives no shadow. 

I have changes no other setting in these three renderings than the ies files.

[Anonymous · Accepted solution]

I came to the conclusion that the "shadow" is part of the IES information. Simply reflects the shadow which the lighting fixture will cast.

This leads to the problem that objects in the family cast shadows itself. If possible the objects in the family should be excluded from casting shadows from the IES light source inside the family. This seems not possible in Revit 2018.

[martijn_pater]

...wouldn't the IES correspond to the geometry of the lighting fixture?

[Anonymous]

You are right that the geometry is defined in the IES-file. To my knowledge it is not possible to get Revit to "generate" this geometry. It would also only be cylinders and boxes which is not the detail level I am looking for. But interesting if it is possible to generate/show geometry from IES - do you know if possible?

[barthbradley]

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@Anonymous wrote:

You are right that the geometry is defined in the IES-file. To my knowledge it is not possible to get Revit to "generate" this geometry. It would also only be cylinders and boxes which is not the detail level I am looking for. But interesting if it is possible to generate/show geometry from IES - do you know if possible?

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What do you mean "it is not possible to get Revit to 'generate' [IES] geometry"?  It is possible!  Turn on the Light Source Subcategory to "generate/show" IES geometry. If you are seriously wanting the IES Geometry, you can Export it to CAD and back into Revit.  I can't imagine the why you would want to do this, but it can be done.   Regarding your statement that the IES geometry would "only be cylinders and boxes"; I'm stupefied by it -- or too sober to understand it.     

[Anonymous]

IES contains the geometry from the light as you refer to but also the geometry of the Lighting Fixture defined as a box or cylinder.

[barthbradley]

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@Anonymous wrote:

IES contains the geometry from the light as you refer to but also the geometry of the Lighting Fixture defined as a box or cylinder.

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No it doesn't.

[Anonymous]

Other software are capable to read this information (Screenshot from external editor showing data of the IES-file) and generate simple geometry.