Dome light vs Vray Environment

[Garryclarke]

Hi,

I'm still trying to learn the ins and outs of VRay and have a question regarding the VRay light.

I set up a basic scene and lit it a couple of different ways:
1. With a VRay domelight with an HDR texture
2. With an HDR Texture in the VRay Environment - GI Environment (skylight) override slot.
(I also tried both scenes with just a plain colour)

The domelight took about 4-5 times longer and was noisier (Adaptive DMC sampling).

I realise that the domelight has lots more options but the difference was marked, so I think I'll be using the Evironment slot from now on, but I want to make sure I understand what's going on, why are the results different? and am I missing something important?

[Macker]

I also wouldn't mind knowing why the two differ, as I've had the exact same experiences with the domelight/environment override.

[Guest]

The V-Ray dome light does importance sampling so you get better shadows, the environment slot does not.

[joconnell]

Were you rendering with GI enabled? A hdr in the envionment slot will only act as a reflection map if you don't have indirect illumination on. A hdr in a domelight does raytracing of the hdr whereas a hdr in the environment slot with GI turned on will use whatever GI method you've got chosen in the primary bounce section. The benefit of the domelight is as James says, importance sampling to clean up quicker and also the option to downsample a large hdri when it's being used as a light source only, so you get quicker, cleaner renders again.

[Garryclarke]

Hi,

Yes, I have GI enabled, default settings, with the Irradiance map preset set to 'Medium-Animation' (I have to render 1080p animations). I want to get the lighting to give me a nice skylight, I intend to add a light for the sun to give me some crisp shadows.

If I look closely I'm getting slightly better shadows from the domelight, but the difference is hardly noticeable, however it's much noisier. Domelight = 53sec and noisy - Environment slot 11sec and clean.

[joconnell]

The environment version is using an undersampling method in this case so it'll be quicker than the domelight which is doing brute force per pixel. Domelight is a really quick way to get clean results if you can't use irradiance maps - such as characters that are deforming or transforming in each frame which would cause flickering in GI methods that use shortcuts. The domelight hdr method is far quicker than if you'd set your primary engine to "brute force" which again is a per pixel method similar to domelight, except this time it doesn't get the benefits of importance sampling.

If you're using a hdr for the skies and then a second light for crisp shadows, what might be a good compromise is to use a domelight with a flat colour as your skylight (or the GI override section of the vray environment) to get a simple sky colour which renders quick, a directional light for your sun with vray shadows which again will be quick and then a hdr in your reflection and refraction override slot. You'll get pretty clean and quick lighting from the dome and direct light with lots of control over the softness of your shadows, then the HDR to make your water way more interesting looking.

HDR lighting is always going to be slower than just a single colour in that slot and since you're looking for speed, it might be a good way to go.

[grantwarwick]

It's my advice to never use the environment slot. I tick them on and to black so the 3dsmax environment slot doesn't affect the lighting.

[Garryclarke]

Thanks for the feedback,

I think I'm still missing something (sorry).

This is my test scene:


https://dl.dropboxusercontent.com/u/..._env_light.zip

Rather than a flat colour it's lit with a gradient ramp, with another gradient ramp inside it which as a VrayColor in it with the RGB set to 5. This gives me a nice dome with some colour variation and a brighter area where the sun comes from. This is in the Env slot (if you look at the attached file I've put it in the reflection slot as well just so it shows in the render. I normally would have an HDR skydome in here)

It renders very quickly with GI on, Primary - Irradiance Map (Medium-Animation preset), Secondary - Brute force.

No matter what I do with a dome light I can't get it to render an faster than 4-5x longer, and it's still noisy.

I just can't see the advantage of a domelight, and I really want to understand.

Sorry if I'm being a bit thick.

[vlado]

No matter what I do with a dome light I can't get it to render an faster than 4-5x longer, and it's still noisy.

This is a very smooth HDR map, without too much contrast and it works fine with GI alone. However if you use images with greater HDR range which are expected to produce sharper shadows, then you'll find out that the dome light is better.

Best regards,
Vlado

[grantwarwick]

Thanks for the feedback,

I think I'm still missing something (sorry).

This is my test scene:
[ATTACH=CONFIG]17319[/ATTACH]

https://dl.dropboxusercontent.com/u/..._env_light.zip

Rather than a flat colour it's lit with a gradient ramp, with another gradient ramp inside it which as a VrayColor in it with the RGB set to 5. This gives me a nice dome with some colour variation and a brighter area where the sun comes from. This is in the Env slot (if you look at the attached file I've put it in the reflection slot as well just so it shows in the render. I normally would have an HDR skydome in here)

It renders very quickly with GI on, Primary - Irradiance Map (Medium-Animation preset), Secondary - Brute force.

No matter what I do with a dome light I can't get it to render an faster than 4-5x longer, and it's still noisy.

I just can't see the advantage of a domelight, and I really want to understand.

Sorry if I'm being a bit thick.

One casts importance shadows and produces detailed GI, the other is a washed out piece of shit? I don't get what you are missing here man.

[joconnell]

If you've got full control over everything and don't specifically need to use a HDR then keep going as you are. Possibly try light cache as your secondary too - the use "light cache for glossies" can speed things up a lot (if you're using glossy shaders).

If speed is still the main thing you're looking for and if all of your scenes are outdoors - maybe look into trying the vray ambient light and popping a dirt map into it's texture slot - it's a fake but if you're happy with the look then why not?

[trixian]

I'd add that making a habit of using a dome light instead of environment maps/environment overrides is good practice, as the dome light lets you set it to irradience map mode, where you can control it's quality through the samples parameter (needs to be quite high) individually from the rest of the GI solution if you need.

As for VRayAmbientLight, I have yet to find an instance where it actually makes things faster than using a straight dome. I have actually experienced renderings slower with the ambient light (with dirtmap added), so I pretty much ignore it completely.
It could be my lack of understanding though. After the "understanding the dmc sampler thread, I might be better equipped to test it again.

[Garryclarke]

OK I get it now.

My test scene was just large spheres on a plane and it wasn't very good at showing the difference between the quality of the shadows.

I added some smaller more detailed objects and the difference became more apparant. I also bought one of Peter Guthrie's HDRs and it looks great (and highlites the difference even more). I'll be sticking with the domelight from now on.

Thanks for the help, I really do appreciate it.