Light Bulb - aka "Come on, baby, light my bulb!"

The Twilight Render Team shares tips, ideas, helpful hints, and more on using Twilight Render
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Fletch
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Light Bulb - aka "Come on, baby, light my bulb!"

Post by Fletch » Fri Jun 10, 2011 3:31 pm

If you have a light bulb, and want it to appear lit, you can paint it with a light emitter material, and it will emit light.

This approach results in a problem. Each rectangle in the geometry of the bulb will be subdivided to become 2 triangles. If the Bulb has 500 triangles, the scene will be now render as slowly as if you just placed 500 lights into the scene. This will render OK in some circumstances with Easy 09. But this should be avoided when rendering with Easy 1-8.

Easy 08 is for exteriors lit with sun and sky, use it for this.
So let's look at scenes rendered with Easy 1-7. You can render the above scenario with a modified preset. To learn more about this, study this thread: Easy 1-7 Photon Mapping and Final Gather (Biased)

Without dealing with changing render settings, the easiest way is to change the emitter material to a "fake" emitter type in the Twilight Material Editor Dialog. Then place a pointlight inside the light bulb geometry. The pointlight will be the light that is now missing because you have changed the material to be a "fake" emitter. When rendered, the light bulb geometry will still cast a shadow, even though it is set to be an "emitter" even a "fake" emitter. So now UNcheck the "cast shadow" box in the Fake Emitter material. The light will be able to shine out now.
LightMyBulb.jpg
LightMyBulb.jpg (135.65 KiB) Viewed 6778 times
If rendering in Easy 09 or Easy 10, try using the Sub Surface Scattering Material Template for the bulb with a pointlight inside.
LightBulb-Material-Easy09.jpg
LightBulb-Material-Easy09.jpg (108.79 KiB) Viewed 6527 times
Another example of the "cast shadow" box being important is when the Light Emitter is used on a surface placed outside of a window to simulate a lot of exterior light flooding in through the window. Unchecking the "cast shadow" box will allow the sun to still shine in through the window and cast sun shadows.
Subject: How to make this material ?
Lampshade-Red-Medium_emitter-castshadowoff.jpg
Lampshade-Red-Medium_emitter-castshadowoff.jpg (77.7 KiB) Viewed 6563 times

designofsoul
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Joined: Tue Aug 30, 2011 7:17 am

Re: Light Bulb - aka "Come on, baby, light my bulb!"

Post by designofsoul » Tue Sep 06, 2011 5:00 pm

I cannot create the effect of light coming from outside..


designofsoul
Posts: 17
Joined: Tue Aug 30, 2011 7:17 am

Re: Light Bulb - aka "Come on, baby, light my bulb!"

Post by designofsoul » Wed Sep 07, 2011 11:19 am

I followed the instructions but I think something is missing ... the light does not come out of the window and even though I turned off the shadows from the left..
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Camera da letto 00.jpg
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Fletch
Posts: 10321
Joined: Fri Mar 20, 2009 2:41 pm
OS: PC 64bit
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Re: Light Bulb - aka "Come on, baby, light my bulb!"

Post by Fletch » Wed Sep 07, 2011 4:44 pm

Be sure no faces are reversed in the model.
Light through the window:
place an emitter surface outside the window and use Twilight Library material "Lampshade Amber Dark" for the window shade. I think it looks very good. (the color should be tweaked by opening the material library in Kerkythea and creating a few new colors.)
Be sure to use Thin Glass for the window glass. Be sure there are no reversed faces and that no groups or faces are painted on the back of the glass with some other material except thin glass.

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