Newbie - getting set up for interior GI

[vrayjoe]

I've just installed the 30-day trial in Sketchup 5 and need some help getting started on understanding the basic approach and settings for interior lighting. Here's my scenario:

I have a large room with some adjacent rooms separated by glass storefront windows. This is a lab so there are no windows to let daylight in. So essentially I'm starting with a dark room (see test render below).

Here's what I need help with:

- I'd like to set up some kind of General Illumination (GI) that would illuminate the room to a level of light that would seem normal to distinguish everything. I do have lights on the ceiling but just placing rectangular lights up there seems to give a very "dungeon" like lighting result. I guess I just don't quite understand GI and what the basic setup should be. There are so many settings and just playing with them in different combinations doesn't work and the manual doesn't really seem to explain the CONCEPT. I don't really need to do any fancy lighting effects at this point.

- Can I draw a shape and then specify it as a Vray light? For example, I have a ceiling surface and maybe I could specify that surface as a light and then just give it a lower light output for general downlight illuminance of the space.

- Lastly, I tried to draw a rectangular light and then include it in a Sketchup component so that it would be multiplied many times around the ceiling rather than drawing tons of idividual ones. But this didn't seem to work. Does Vray have a problem with lights that are part of Sketchup components/groups?

I'd really appreciate any help with this as I know this software can do what I'm wanting it to do but I just feel like I stepped into a 747 cockpit and don't know what button to press first!!

Thanks.

[joe_b]

Re: Newbie - getting set up for interior GI

- I'd like to set up some kind of General Illumination (GI) that would illuminate the room to a level of light that would seem normal to distinguish everything. I do have lights on the ceiling but just placing rectangular lights up there seems to give a very "dungeon" like lighting result. I guess I just don't quite understand GI and what the basic setup should be. There are so many settings and just playing with them in different combinations doesn't work and the manual doesn't really seem to explain the CONCEPT. I don't really need to do any fancy lighting effects at this point.

Global, or Indirect, Illumination is just a means of bouncing light around. In reality a lot of the light that falls on objects are secondary bounces of light - not just the direct light rays hitting it. So when you enable GI you are just calculating the various bouncing of light. The settings for GI can be overwhelming - but in reality you probably don't need to concern yourself with too many of them until you are more comfortable with them. For an interior shot I would use Irradiance Mapping as your primary engine (You can set that in the Indirect Illumination tab of our options ). Put QMC( Quasi- Monte Carlo Integration ) as your secondary engine. I think as a beginner you can probably get away with the default settings.

- Can I draw a shape and then specify it as a Vray light? For example, I have a ceiling surface and maybe I could specify that surface as a light and then just give it a lower light output for general downlight illuminance of the space.

You can use an emitter material to generate light from any surface/object you please. I don't really suggest this as the main lighting for your scene because the emissive materials don't get sampled as well as rectangular lights. I'm thinking that if you have a dungeon look with a rect light then you probably just need to turn the multiplier of the light up so it is more powerful. You may also want to just use the standard camera for now - or disable "exposure" from the physical camera settings because the physical camera's default settings are for a sunny outdoor scene - thus using exposure may darken your image if you have not adjusted the exposure settings. The standard V-Ray camera is just a simple pin-hole camera that does not pay attention to exposure settings - so it might be easier for you at first to just use that. If you do this - make sure you are not using the physical sky in your environment settings or your scene will probably get over-saturated

- Lastly, I tried to draw a rectangular light and then include it in a Sketchup component so that it would be multiplied many times around the ceiling rather than drawing tons of idividual ones. But this didn't seem to work. Does Vray have a problem with lights that are part of Sketchup components/groups?

That is a bug we're fixing in our service release. Apparently they will work ok in groups sometimes but not in components. So you might want to avoid that for the time being unfortunately.

[dalomar_cg]

Re: Newbie - getting set up for interior GI

As far as secondary bounces go, LC is going to be a much better bet as it allows more light into the scene (calculates more bounces) and is much quicker that QMC. You will loose some detail, but that can be easily adjusted.

The trick (in my mind) for interiors is to work with the physical camera. You can set your lights at a given intensity (at some point in the future this will be a physically based unit, but for now you can set it some what arbitrarily) and then adjust your exposure in the camera and get the desired affect. There will still be a little tweeking of your lights, but it won't be nearly as much.

[vrayjoe]

Re: Newbie - getting set up for interior GI

Thanks for the responses and advice - I really appreciate it.

Now that I have all of my lights in place, I'm finding that the rendering process quits part way through. I have an array of fluorescent lights on the ceiling and this seems to be too much for the process to handle. I'm running this on a Windows XP virtual machine on my Mac (Parallels Desktop), by the way. I'm wondering if this is a problem or reduces processing speed? Below is the Sketchup model with the lights and the error message I'm getting after about 2 hours of rendering.

I'm wondering if anyone has ideas of how to simplify my lighting. I need the array of lights to be "shining" but perhaps that would be more efficiently achieved in Photoshop afterwards. Could I maybe turn the whole ceiling plane into an emmissive material that would illuminate the space? I eventually need to output a very high resolution file and with this 320x240px test taking hours and failing before it's finished, I'm not sure what my options are.

One last thing. In the Sketchup 5 version of Vray, is it possible to select all my copied lights and adjust the intensity in one shot? It doesn't seem so.

[dalomar_cg]

Re: Newbie - getting set up for interior GI

I'm not 100% sure if the error could be because of running on parallels...that is certainly not my area of expertise, so I'll leave that as my general hypothesis.

As far as your rendering taking hours, it seams to me that you haven't changed much of the default settings. If thats the case, then you probably have QMC for primary bounces which is the slowest calculation method (especially for interiors). Irradiance map is your best bet. Just change from QMC to IR in the GI rollout. Then change the min/max rate from -3/0 to -4/-1 and you should be good to go. If things are still a little splotchy then you might want to increase the Hem.SubD to 60 or 80.

I don't recommend just making the whole ceiling a self emitting material, as this will cause significant artifacts on a surface that big...if you want to break it up into smaller sections (like the size of individual lights) thats fine, but not a big surface like that.