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hobick

Can a glowing object be invisible but still emit light?

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Hello all,

 

I have a structure modeled and I need to light it internally. Wondering if there is a way to make an object with a glow texture emit light but render invisibly and not show up in the render. I know that when using an area light this is possible but the results of that approach create a completely splotchy light effect. Is there something I can do with my glow texture to achieve this? The attached image on the left shows the approximate glow effect I want but I don't want the object itself to show up. The image on right is without the glow and shows the interior space I am trying to light.

 

Any tricks I am missing here?

Screen Shot 2018-07-14 at 9.55.47 AM.jpg

Screen Shot 2018-07-14 at 9.58.54 AM.jpg

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As far as I remember it is not possible.

Even in full C4D when  Visibility for Cameras was set to OFF.

 

I had to use VRAY to make my typical Polygon Array Interior Fake Lights working.

No problem in Modo.

 

 

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Posted (edited)
  • Create a Nurbs Surface from the white strip that you want to glow.
  • Delete the strip leaving the nurbs surface
  • Convert the Surface into an Area Light
  • Make sure Render Geometry is turned off. Brightness value, say: 5000 lumens, Quality: high

That should do it. Works here.

 

The light source is in between the red panel and the mesh

Screen Shot 2018-07-14 at 18.28.59.png

Edited by markdd

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I don't think it's possible, no.

 

If you can't get an area light to render more smoothly after playing with quality settings, as another approach, what about making the blue texture itself glow? You could make it a blue gradient image instead of flat blue to help the effect.

 

Even if it's not what would be happening in real life, it's often smart to fake things in renderings to get the desired look.

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Either extract a nurbs surface from the back of your grill move it off the back of the grille by 0.001mm and attach the Glow Texture to that or

Add a transparency to the glow texture that matches the openings in your grille or

 

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4 hours ago, markdd said:
  • Create a Nurbs Surface from the white strip that you want to glow.
  • Delete the strip leaving the nurbs surface
  • Convert the Surface into an Area Light
  • Make sure Render Geometry is turned off. Brightness value, say: 5000 lumens, Quality: high

That should do it. Works here.

 

The light source is in between the red panel and the mesh

Screen Shot 2018-07-14 at 18.28.59.png

 

Thanks! I tried this approach but am still getting the blotchy mess that area and line lights always seem to create. Even at very high quality setting. I turned off the perf panel to show it more effectively. It's kind of hard to see but  yours does look smoother.

 

 

Screen Shot 2018-07-14 at 2.32.21 PM copy.jpg

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4 hours ago, Andy Broomell said:

I don't think it's possible, no.

 

If you can't get an area light to render more smoothly after playing with quality settings, as another approach, what about making the blue texture itself glow? You could make it a blue gradient image instead of flat blue to help the effect.

 

Even if it's not what would be happening in real life, it's often smart to fake things in renderings to get the desired look.

Yeah I wind up faking things a lot in VW and I might have to go this route and make custom texture that fakes the effect. Would be great if it just worked as an area light should and I didn't have to jump through the hoops to achieve the desired look. 

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Posted (edited)
4 hours ago, bcd said:

Either extract a nurbs surface from the back of your grill move it off the back of the grille by 0.001mm and attach the Glow Texture to that or

Add a transparency to the glow texture that matches the openings in your grille or

 

 

Here's a stab at that approach. The perf complexity certainly slows things down and when extracting the entire surface it gives a very even light to the blue panel as shown. I might be able to edit the nurbs surface such that it is not the full panel but is clipped away a few inches at the perimeter to give the desired falloff of the light on the blue panel.

Screen Shot 2018-07-14 at 2.56.20 PM.jpg

Edited by hobick

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My approach would be the same as Andy’s above: create the blue surface texture and apply a glow to it. 

 

The question to ask ask is how would this work in the real world?  My assumption is that the blue surface is a back lit translucent plastic. If that is the case, then I would absolutely create an image that has the proper gradient, (I often do these in greyscale so I can easily change to color of the “light” by changing the object color or, more typically, assigning the object to class by color and changing things globally that way). Assign a glow texture to it, add a bit of reflectivity as well if it is smooth plastic and you should be good. Realism vs rendering performance will determine if you want your texture to emit light. The reflectivity makes a HUGE difference in realism. 

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I would agree with Scott more on this.  

 

Im actually dabbling with something very similar.  I wanted to ask are you doing this in a design layer? Also did you find you had to add a light object and then turn that object off to get this effect?

 

Seems to me I always have to add a light object and then turn that off to avoid the default lighting in the program that is present in the event of no light objects.

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You can only make Light objects, or line/area lights emit light without being visible at all themselves. Objects with Glow textures applied; when you reduce their transparency, will also proportionately reduce how much light they are emitting so by the time they're 100% transparent, they are emitting 0% light.

 

1 hour ago, HEengineering said:

Seems to me I always have to add a light object and then turn that off to avoid the default lighting in the program that is present in the event of no light objects.

This is true, glow texture objects alone won't disable the default lighting yet, but I've requested that they do.

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Just wanted to loop back around on this. I wound up using a combination of glowing objects and a simple custom texture for the blue panel. I essentially modeled thin strip lights on the inside faces of the front and back extruded frame as well as in the reveal at the inside edge of the perimeter and around the floating panel within the structure. All of these received a white glow texture. I then did a simple light to dark blue gradient to amplify the glow effect of the lights within the perf panels. And yes, I did have to add a light turned off to override the default ambient lighting. I rendered with a custom render style.This is how it turned out in the end. And in case anybody wants to get a similar effect, I've included a screen grab of all of my render settings.

render.jpg

settings.jpg

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Could you share the file as well? I’m curious about the mesh texture you have used. You appear to have rendered the mesh walls which I have never succeeded in doing and would like to see the texture you have used.

 

Great result, thanks for sharing. 

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Posted (edited)

Could this be done as well using an alpha channel in a perforation texture applied to the curved panel (like you ‘normally’ do for a fireplace). The glow will come through the perfs as well, but the texture can be adjusted more easily afterwards…?

Edited by Jan-Burger TROOST

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Posted (edited)

I needed the perf to actually have thickness so I wound up modeling it in 3D. Don't recall if I cut circles out of 2d rectangles then extruded or extruded first then did solid subtraction. This certainly took a huge toll on rendering times but did give me the result I was looking for with the edges of the holes having surfaces that could be illuminated. It doesn't have a texture...just a white fill.

 

I did do a pass using just an alpha channel to create the holes but this doesn't generate side walls for the holes which is something I needed since some of my renderings needed to be closeups. The alpha channel method just creates two surfaces. There may be a trick I am unaware of. If so, would love to hear it.

 

detail.jpg

Edited by hobick
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I don't think there is a trick, that's why I was curious. It would be fantastic if the Alpha channel route could be made to add walls to the holes it creates. I did once fiddle about with displacement mapping for this but didn't really follow it through.......

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I think I went the same route a while back trying displacement and bump mapping. IIRC the results were always kind of crude and it never created crisp results. Eventually gave up.

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If you’d make it a nurbs, can it be tricked using the 3D modelling > extract surface option? Will it have holes in it because of the alpha channel? #imcurioustoo

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