If I’m doing a GI animation, what is the difference between illuminating the scene with a dome light vs. a colored environment background?
I’m not using textures or anything -- just solid color, but if textures were involved would it change the answer?
I u want to know the effects on results and not technically the differences about how they work, I can say dome give u the best indirect light details even on very little geometry (proper shadows of an object too not only casted shadows of it) but is very slow compared to environment one and this last one lack respect the dome a lot of details it can be avoided only raise up the irrad map parameters.
I’d suggest to do a search with AND dome in this forum and u will find a lot of useful posts about dome light 
Excuse my bad english
with the environment you’ll have noise in some case when there isn’t any light, with the dome you can avoid this but with a big time cost !
Ive found with skylight its more splotchiness to be concerned with, with dome light its noise.
Yep splotchiness, my apologize, In fact I would like to said that you can avoid easily the noise with the subdiv, but for the splotchiness it’s more difficult.
guys…
dome light is a light source, therefore it has no gi rays, just direct rays. It does not produce splotchiness, just noise. Its great to be used in the exterriors. Skylight, as in environment sky is gi dependant. So whatever your gi solution is, that you will get in your renderings. I can most defenently recomend dome light for exterriors, as a primary illumination.
OK man…
The dome light has also another great benefit (compared to using the same map in the environment with just QMCGI as primaries): importance sampling.
With a proper HDR (try kitchen, for instance) you’ll get splendid caustics and shadows traced from the map, without resorting to awfully high sampling rates (subdivs).
That’s because vray prepares the map and checks where the most light comes from, preferring to sample those areas.
It can be used to great effect also for product shots, as it’ll produce a very accurate lighting environment (with, for instance, studioHDRS from dosch).
Or so i believe, lol 
Lele
The new dome light (well… newish) is fairly amazing because the rays are adaptive. Meaning that brighter areas of the image case more rays than dimmer areas. This allows Vray to get sharp shadows from HDRs, in a very efficient way. No other program that I know can do IBL as efficiently and accurately as this. Even Paul Debevec was impressed when I showed him. I never use the skylight anymore. Also keep in mind that if you use the domelight, as Dmitry is saying, it is a light source. So, if you are only interested in the primary light of the environment, you may not even need to turn on GI.
:lol:
the only drawback is that in areas where the geometry in scene in not lit by direct light you get totally black surfaces (like parts of a model perfectly parallel to the ground plane).
here’s an example:
no gi
here’s the same with gi turned on (only the first bounce):
and just for the sake of it, since it’s a very popular topic these days 
: these two above were rendered with lele’s 0.255 method, while this last one has gi turned on, but no vraycolor map dimming mat and reflections. it took more than twice the time to render and it doesn’t look as good:
dome light texture is one of debevec’s skyprobes.
Those look good. ya its not good with no Gi depending on the view.
Thank you for all the posts.
However, I think there’s something I’m not understanding. I see that I can use the domelight as a primary source light for nicer shadows etc or for IBL which I’m not doing here.
But what if I choose -- Store with Irradiance Map? That makes it indirect doesn’t it?
In that case, does it become the same as an environment skylight? Or is it still different?
I’m interested in SPEEDY animation rendering. That’s why I’d prefer to use the indirect irradiance method than direct light. It seems to render damn quick once the IRR map is calculated.
But what if I choose -- Store with Irradiance Map? That makes it indirect doesn’t it?
As far as i understand (wich isnt very far :P) This doesnt make the light behave like indirect light. it is just stored with the irradiance map hence you can turn it off at rendertime to save rendertime. that will also loose detail tho. But it’s not the same as indirect light. Someone correct me if i’m wrong.
Thorsten
if you turn gi on, then vray will calculate both direct and indirect light (more than one bounce if you have primary and secondary on), which in this case comes all from the domelight (if you don’t have any other light source in scene, that is).
storing it with irr map doens’t make it indirect, what makes vray take into account indirect illumination is whether or not you have gi turned on.
as instinct says, when stored it’ll render much faster, but then I guess its sampling will depend on your irr map settings. you may loose detail but get a way too smooth, even though faster, render.
Some tests…
Kitchen.hdr as BG map + irmap primary only (settings posted later on):
No BG / GI, Direct computation, 24 subdivs, 1024 resolution:
No BG, IRMap GI primary only, store with irradiance map, 64 subdivs, 1024 resolution:
All in all, one more confirmation of VRay being an absolutely smacking all-rounder…
Lele
I think I used the wrong terminology.
I see that the dome still has a direct component even when stored in GI. I guess I wasn’t sure what exactly happened to the Direct Lighting once it got stored as an IRR map (vs. not stored and vs. the environment light).
Once the dome is stored in IRR -- is it susceptible to the same issues of splotchiness as the env.light?
ALso…
it is just stored with the irradiance map hence you can turn it off at rendertime to save rendertime
This isn’t quite correct is it. You don’t need to turn the light off. If it’s stored in IRR and you’re rendering from a pre-calced IRR file, the dome light is ignored anyway since it’s baked in, right? Turning it off won’t help anything will it?
Yeap… that is why I hate the concept of Ambient Occlusion so much. I talk about that on my DVDs. However, if you are doing character work which conditions such as these don’t happen as much, GI is not as needed.
Now try your test with an HDR with a very bright source such as a direct sunlight.
Apart from importance sampling threre’s another great difference - domelight as beeing a light source is producing speculars, and as they are based on the map in this case real nice ones. They can be treated separately in render elements. Drawback is, that the “environmental lighting” is now stored in the lighting elements and no longer in gi.
regards,
Michael
