Intermediate mental ray Lighting

Written December 21st, 2008
Categories: Articles, Lighting, Rendering / Compositing
25 comments

Hello everyone!

Welcome to the second mental ray lighting tutorial.  In this feature, I’ll be walking you through a typical lighting project for a scene I built for one of my Monday Movies.  Remember that this isn’t the only way to illuminate a scene, and your render times could get pretty high.  We’ll be using mental ray Sun&Sky to get the base lighting, followed by a few area lights to illuminate the hallway section of the render.  I’ll show you some common settings you’ll need to set up along the way, and by the time we’re done you should have a well lit scene!

You can download the starter 3dsMax Scene Here.

Our final render.

Note that some of these images will have light leaks above the center divider wall.  I didn’t notice these until I was done writing the tutorial, so please excuse the error.  The scene I uploaded for you to start with has been fixed. In addition, at the end I changed the floor to carpet instead of hardwood, so don’t be surprised when you start rendering and notice there’s carpeting.

Our starting point.

Where the magic begins.

Go ahead and load up the file  You’ll notice that there isn’t any lighting, but the materials work together pretty well.  I’ve gone ahead and included some little details such as the coffee maker and the tree.  However, you’re free to add anything you’d like!  Throw in a conference table for good measure, or some blinds on the windows if you’d like to be extra classy.

Our unlit render.

If you take a quick render, you’ll notice that the lighting is unimpressive, but the materials are right and the modeling is diverse enough to give us a good outcome once we’ve started lighting.

mr Sun & Sky Light Source

Create a mental ray Sun & Sky light.

The first thing we need to do is create a daylight system in 3dsMax.  Day-time renders are a piece of cake because most of the lighting comes from outside.  Under the “Systems” tab of the modify panel, you’ll see “Daylight”.  Create a daylight system by clicking and dragging to create the compass rose, followed by another drag and a click to create the light.  If you get a dialogue asking if you’d like to use photographic exposure control, click “Yes”.  It will yield good results and is vital for this tutorial.  The direction of the light doesn’t matter.  Click on “Manual” under the “Position” group in the modify panel, and you can then drag the sunlight light wherever you want.  I recommend a glancing angle that bounces the light off the floor and wall.

Scene Overview

An overview of the scene and setup.

Ignore the box you see on the open face of the building.  It’s a little hack that lets you see inside a wall while keeping it inpermiable to light.  That box is renderable and only casts shadows.  The rest of the walls have a shell modifier on them.

The next step is to set the daylight object to mr Sun and mr Sky.  I know it seems like this should be on by default, but there are times when you’ll need to use IES.  This isn’t one of them though.  By setting the daylight to mental ray Sun and Sky, you’ll be tapping into a powerful natural lighting engine that can make just about anything look awesome.  If you get a dialogue asking if you’d like to set the background to the mr Sky map, click “Yes”.  It’s just a good idea if you’ve got nothing else for a background.

Sun & Sky Parameters

Setting up mental ray Sun & Sky.

Go ahead and take a quick render.  You’ll see that our scene’s lighting has changed dramatically, and Final Gather is now giving us a little more depth.

First Architectural Render

Our first render with only the outdoor light.

Comparable to a real-life photograph, the exposure is adjusted to make the outdoors look reasonable at the expense of making the indoors too dark. We’ll increase the exposure shortly. First, we’ll help mental ray understand that these windows boarder the outside world, and should therefore bring in a little more light.

Under the “Create” tab, under the “Lights” section, you’ll find mr Sky Portal under the “Photometric” group. The mr Sky Portal can be put in the window frames to boost the lighting, and basically earn us an additional Final Gather bounce for free.

Create area lights.

It’s important that they reasonably approximate the window frame. It’ll take some guessing and checking, but it’s worth it. You’ll also want to enable the “From ‘Outdoors’” checkbox, if available.

Setting up sky portals.

Set up your mental ray Sky Portals.

Now that the sky portals are set up, take another render.  Notice the difference between this and what you had before.  The additional light is clearest on the ceiling and the blueish glow on the wall.

Render

Render with your new Sky Portals.

But the image is still too dark!  Like I mentioned earlier, our exposure is set to make the outdoors look normal at the expense of how the indoors looks.  Let’s increase our exposure such that the indoors looks normal and the outdoors looks blown out.  Open your Environment and Effects window (hotkey ’8′) and set the exposure value to 11.  Don’t hesitate to try other values and see what you think.  This is a very powerful mechanism for altering the brightness of your renders.

Turn your exposure values up to 11.

Here’s what my render looks like with a value of 11.

Render at an exposure value of 11.

We’re looking good!  But the hallway still doesn’t have any light.  The client won’t like that one bit!  Let’s add some lights to the lamps hanging from the ceiling.  Select a “Free Light” from the photometric group in the lighting section of the create panel, and place it in the light trough of one of the lamps.

Place the light in the light trough.

In this case, we want to use long cylindrical lights like fluorescent tubes.  We’ll need to select “Cylinder” under the “Emit Light From (Shape)” group.  We’ll also need to alter the length and radius of the light to fit nicely in the trough.  Finally, be sure to enable “Light Shape Visible in Rendering” so that it actually appears as a tube!  It’ll look great with the semi-transparent material I used.  Finally, we need to set up the shadow casting.  Select “Raytraced” from the pulldown under the “Shadows” group, and then click the exclude button.  You want to exclude the light troughs because otherwise they’ll create abnormal shadows on the walls.  From the list that appears, select Cylinder02, Cylinder 03, Cylinder09, and Cylinder10.  Sorry for the lousy naming conventions- these are the troughs.  Finally, select Exclude from shadow casting only; we still want the troughs to light up!

Set the area light parameters.

Here’s a render showing where we are so far. The hallway is starting to light up nicely, and the conference room looks like it might actually make meetings fun. This is really going to blow away that client, but we’ve still got a little ways to go before it’s perfect.

The render's starting to come together.

From here, let’s bump up the mental ray settings a little.  The Final Gather bounces are still on zero and very low precision.  The bounces value can be changed to 1 and the Final Gather Precision slider can be moved to “Low”.  The renders will take longer, so don’t hesitate to lower these back down until the very end.  I’m just increasing these to get closer to my final render.

Increase the Final Gather bounces for more light.

Here’s what the render looks like after the increases.  There’s a little more light in the corners as the Final Gather bounce pushes the lighting into recessed corners.  It’s a subtle, but important difference.

A render after increasing bounces.

We’re almost done!  I just want to add two more things.

The first is a light around the corner in the hallway to show that it’s a corner and to imply that the building is larger than just what’s in the field of view.  I accomplished this by using a “Free Light” (like in the lamps), only this time I’ll be using a rectangular area light.  This will create better shadowing by the door, and make it look like there’s more natural light (like from the other side of the office building).  Be sure to increase the brightness a little (I used 2000 cd).

Add another area light for depth.

The last thing we want to do is boost up the lighting in the hallway.  Right now we’re only seeing what the four florescent lights are generating with the help of the Final Gather bounces.  Unfortunately, it’s a little rough between the two lamp units so we’ll want to throw in an ambient-only, standard omni light to brighten it up a bit.  Notice that you’ll need to use an abnormally high intensity in order to compete in the photographic exposure control solution.  If you didn’t have the exposure control on, the image would be pretty much all white.  You can use my setting of 200 intensity, or experiment to see what works for you.

Include an ambient-only light.

And that’s all there is to it!  Take a look at the render below to see the final outcome. Just for kicks, I changed out the floor material for a carpet because that suits the “office” theme a little closer.

Our final render.

I hope you enjoyed this tutorial, and learned a little more about lighting a scene using mental ray.  Stay tuned for my weekly Monday Movies, and, until next time, happy lighting.

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