Why use Blender's 'lights' over just a mesh with emission?

Im trying to wrap my head around lighting, especially for archviz projects.

This might be obvious, but can anybody tell me why I should use actual lights (area, point, etc) to light my interior and exterior scenes? (im not talking about the sun and actual outside world light…but more about garden lamps, spotlights in the wall, room lights etc)…

Why can’t use a mesh with a emission shader on it? Because that lets me use the array modifier which is handy…

Is it more realistic to use those? More control about direction and stuff?
Or is it that only using those lights (sun spot, point etc) will enable me to use IES tetxures?

I have not yet worked with emission textures! Maybe the shadows will make the difference.

Lamps:
Can use IES for certain types (Cycles only for now).
Cleans up faster.
Can not be seen by camera.
Have fewer options.
Obscure texture coordinates (have to look in the manual every time).

Emission:
Easy to texture.
Must be used for camera to see them.

You can use emission all you want, except for IES. But they are not as efficient to sample as lamps. If I can, I will use lamps all the way - and I’m annoyed as I can’t simply make the lamps camera visible but instead have to create geometry. Can’t even convert lamps to geometry. Can’t remember which, but there are things that are not supported with nodes as well.

Wishlist:
Camera visible analytical lamps.
Analytical tube lamps.
Analytical sphere lights.

Edit: And right now with the version I have, it seems that analytic light texturing is completely broken. I didn’t check the manual, so I might have tried something wrong. Anyone care to check?

Edit2: Furthermore, it seems that analytic spotlights scene instanced to the scene does not adhere to spot shape size (cone angle) in the source:

Notice how the editor from 180deg to 90deg is only reflected in the active rightmost source and not the target spotlights which remain at 180deg. A nightmare…

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If anything used to work, but is working no longer, then it needs to be reported to the tracker.

About lights vs. emission meshes though, the built-in light types have a major sampling advantage if you use Branched Path Tracing (as all of them will be sampled at once instead of a random one each pass). However, emission materials are needed for things like glowing gas, fire, or lights with very complex shapes.

Thanks for your reply’s guys

So let me get this straight, the best way (and fastest) way to create realistic lighting in archviz scenes is to use Lamps as much as possible? And if i DO want the lightsource to show… like in @CarlG’s example… Do you just create a circular mesh, put a small emission on it…and then put the lamp ‘outside’ of it? Is that how it works?

And what does this mean?

About lights vs. emission meshes though, the built-in light types have a major sampling advantage if you use Branched Path Tracing (as all of them will be sampled at once instead of a random one each pass). However, emission materials are needed for things like glowing gas, fire, or lights with very complex shapes.

How would I use Branched Path Tracing

Analytic light texturing worked again (kindof?) on the version I downloaded at work today. Not the same coords as I remember, but I forgot to test IES.

Here is where you can enable that in 2.79:
image

And here is a post showing a good use case for branched path tracing:

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I put mine in front of it to make it easier to select if I need to tweak it. Also, the emission shader you may want to keep it under wraps so as to not produce any overbright aliasing artifacts. I try to also add a unique material ID to it so I can glare it selectively in post.

The emission based should be camera visible only.
The lamp based should be visible to anything else (can’t be camera visible anyway).
Make sure you match the color of them, but the brightness can vary - superbright aliasing issues are not generally a huge problem in reflections since they tend to be warped and roughed out.

Fastest way to create is just to use emission based.
Fastest way to render is to spend more time setting it up with lamp and emission.

Also, for archviz I guess you sometimes need to do translucent lamp shades. Instead of relying on translucency shader to create extremely noisy indirect light, you can fake the lamp shade and basically paint the emission onto it. In that thread I’m using math nodes but you get the idea. This light acts as a direct light source and generally renders with much less noise. It also helps that the shade has some good surface area to it, as tiny lamps are much harder to sample.

Hi @CarlG

Thanks for you reply. Its a bit more clear now. Couple of questions though

  1. when you say… in front of it… .Do you mean you put the light outside the mesh? And by keeping the emission under wraps…you mean using a lower strength?

And finally…you say " I try to also add a unique material ID to it so I can glare it selectively in post."
I now how to ID an material…but can you elaborate on the workflow to use this to add a glare in post? You mean photoshop?

And thank you for that lamp shades shader. Thats definately something i can use later on.

Yes. I’ll typically use a spotlight slightly below the emission surface. Since that emission is for camera only, it won’t really illuminate the light cylinder itself, but I use fixtures where I don’t have to factor that. If critical, I’d paint it on as a texture rather than rely on physics. Bright light sources (inverse square law) very close to glossy surfaces I think can be problematic wrt firefly creation (I prefer not to clamp anything).

Yes, lower strength for camera to avoid stairstepping aliasing from very bright surface contrast.

Glare node in Blender Compositing. Either just fog glow or also streaks for very tiny light sources. Convert ID mask for the selection. I typically do mix at 1 and add them with selective strength later.