Headlights and cherrytops...

[shura]

wow, this is very smart! took me a long "errrrrrrrrrr" to understand the trick... this may help reducing rendertime with emitters. thanks for this one.
cheers
alex

[tomsdesk]

Okay...tried it all (right away, actually, but didn't have a chance to post the results till today), thank you very, very, much for the tips, and settled on using "wax": with a slight transparency set in SU (see below).

Hey Fletch: finally discovered you had painted the back sides of the cube faces which brought up all kinds of questions. Any chance there is (or could be) a primer on back faces in Twilight and when adding a material to them is necessary/recommended.

[Chris]

Adds a big improvement, definitely.

In general, there is no benefit or use to painting back faces. Twilight will try to 'accomodate' back faces, but there is no advantage or special feature to doing so. It should be avoided if possible.

[olishea]

haha is this a murder scene?

[vizfellas]

I think it is a CSI - Twilight team

[Fletch]

no trick for back face, just an 'accident'... which seems appropriate considering the scene here.
with fake emit, back or front face doesn't matter... with real emitter - it would matter A LOT

[tomsdesk]

... with real emitter - it would matter A LOT

How so?

[Fletch]

light emits from the front of the face

[Chris]

... with real emitter - it would matter A LOT

How so?

This is somewhat of a difficult question. Twilight uses a material priority order to accommodate SketchUp's 2-face material system. You can find more about it here.

How it's relevant to emissive faces is this:
If you have 1 material applied to a face, Twilight will assume that whichever face it is, front or back, that you mean for it to be the 'important' face and so will internally orient the face correctly. So if you apply an emitter to a front or back face, as long as that is all, there is no problem.
The complication comes when you have a group or a component. If you apply an emitter material to a group or a component, Twilight can't 'reorient' back faces because it doesn't know which face is important, the front or the back. So it simply assumes you want the front face (unless the front face has it's own material, then it uses that). If the face is backward from what you intended, your emitter will be emitting backward.
The solution to this is either apply your material directly to your faces, on only one side, or make sure your component or group has all of the front faces facing the right way.

[tomsdesk]

Thanks, Chris, I think I have it...except for on thing: I've been picking a face to apply a material in twilight regardless of whether it is in a group or not, is it possible to apply a twilight material to a whole group at once (like applying a paint sheen to a whole group of different colored faces)? Hasn't seemed to work that way to me so far, though I seldom apply a material to a group or component...except accidentally?