[oz42]

Hello all! Long time no speak (although I have been lurking on the forums from time to time!),

Sometimes when creating interior scenes and I only need a light source need to look 'bright' but don't actually need it to influence or contribute to the lighting of the scene, I used to use a 'fake' light (explained below).

I haven't had to use this method for a while (I'm guessing since v2) but I currently have a very complex interior scene with complex strip lighting and need to try this method again.

The reason being is that the render times with just sunlight (which is all I need to actually illuminate the scene) is 7 times quicker than the version with the emitters as well as sunlight.

So, I want my strip lighting to look 'bright' (i.e. the brightest white object in the scene - much brighter than the surrounding white ceiling) but not actually illuminate the scene (because it slows the rendering down by a factor of 7!)

Previously for the 'fake' light I had used a multiple layered material where I had 8 layers of a diffuse white material on top of each other in additive mode. This used to create a pure bright white object that looked like a light source in the scene but didn't contribute to the lighting or slow the render down; all-in-all a great fix!

Unfortunately this 'bug' seems to have been fixed in Maxwell v3 and no matter how many additive layers I add to a material, it doesn't get any 'brighter'

Does anyone know of any method to create a 'bright' looking light source without it slowing the rendertime down (without resorting to Photoshop and rendering out multiple passes and compositing)

Thanks in advance...

[oz42]

ok, too many words! Here's a quick example from yesteryear;



All mini spotlights (circled in red and similar) are using the fake light outlined above and, I think, look pretty convincing as lights. They don't add to the illumination of the scene (there are other lights in the scene to do that) and so don't slow down the rendering. They even show up a bright objects in reflection (see chrome dome below blue circled light).

They were the perfect solution!

(I know technically this goes away from the non-biased nature of Maxwell but if the render times go up by a factor of 7, I'm happy to use this method!)

[Mihai]

But when you mean quicker, do you mean the Physical Sky by itself (if you switch off the emitters using ML) is 7 times more noisy than using Phy Sky alone? Or does it say the time will be 7 times longer?

What happens if you use emitters but hide them from GI?

[oz42]

My scene is an interior with long strip light along it's length and windows along the side. If I render with both physical sky and strip light emitters the test render (at 1/4 size) takes 50 mins. If I hide the lights in XSI and render again, it takes 7 mins! The level of illumination is about the same - the strip lights don't add much to the interior illumination.

I forgot about 'hide from GI' - I'll give it a go...

[oz42]

No, 'hide to GI' didn't make any difference

I'll render the two versions and show you what I mean...

[oz42]

Thanks again for you help Mihai, hopefully these small test images will make it clearer; (I've removed all the furniture to speed things up)

Lights on - Render time 35 mins;


Lights hidden (and letting sunlight through roof!) - render time 5mins;


As you can see there is not much difference in overall illumination or noise but a HUGE difference in time.

What I'd like is the illumination and render times of the second image but the strip light showing up as bright white. As I say, I used to solve this with my 'fake' light material (multi-additive-layered diffuse material) but this is no longer possible with v3. Any other ideas?

[Mihai]

I guess, render a second time but apply an overall material to everything non emitter and set this material to Matte. Then use your regular emitter material for the emitter surfaces. This will render super fast and you can then easily comp in the emitter render because the right areas will be masked out by the matte material.

Would it be possible to PM me this scene for testing? It will remain with me

[photomg1]

It doesn't solve his lights in reflections though on any objects in the scene that a have any kind of reflection . Cool solution you had going on there for this type of situation oz42.

[oz42]

Mihai; good plan, I'll give that a go today. I'll also PM you the scene (Softimage 2015) but please do not distribute as this belongs to a client!

photomg1; good point. Fortunately the only thing it really reflects in for this scene is the windows and I'm ok if it doesn't. The multi-additive-layered material was a good solution but I think it was a bit of fudge anyway!

Having said that it would be nice to have something similar. Perhaps a special material, like matte and shadow that always renders pure white (255,255,255 in image) that also reacts to bloom and scatter?