|	Tutorial #2 / Natural Lighting
Introduction |	The goal of this tutorial is to set up the lighting for a room which is illuminated by a sunlit window. I'll show you how to create several bouncelights in order to achieve a natural lighting appearance. Please note that this tutorial is for 3DStudio Max, but it should work for other 3D packages accordingly.
Step 1 |	Here is our typical indoor scene: a room with a table infront of a window. You can downlaod this scene here: tut-room.zip. And this is what it looks like when you hit the renderbutton. Yuck!
Step 2 |	First of all let's have sunlight shining through the window. Create a DirectionalTargetLight, give it light blueish color like the sky and set it to cast raytraced shadows. With a multiplier of 1.2 it should render to such an image: Please take note which parts of the scene are hit by the light and which parts remain black, because next we are going to create "bouncelights" for the illuminated objects in order to fake light which they reflect back into our room.
Step 3 |	We see the pale blue sky in the window and also the wall, floor and table being hit by sunlight. Let's begin with some light bouncing off the floor. Create an OmniLight and place it near or even inside the floor. Make sure to exclude the floor from this light and give it the green color of the floor material. A multiplier of 0.3, which is one quarter of the sunlight's multiplier value, should be okay. Adjust the attenuation. Setting attenuation parameters is very important to achieve a natural lighting appearance. I suggest using the "Far Attenuation" spinners for easy handling. Set FarAttenutionStart=0.0, FarAttenuatioinEnd=600.0, as this span fairly includes all of the scene. Make sure to toggle off the "affect specular" option, we want diffuse bounce lighting only. As the floor is being hit by sunlight in the top third sector move the light somewhere into that area. With the floor bouncelight the scene renders like this:
Step 4 |	Now let's have a bouncelight for the front wall accounting for light being reflected back into the room off the front wall. Simply clone the Omni you created for the floor, but give it the yellow color of the wall material. It has a multiplier of 0.3, the sun's multiplier value divided by 4, just to give you a rule of thumb. Remember to exclude the front wall from this light (do include the floor), and place it close to or even inside the front wall, somewhere in the lower third sector, as this is where the wall is mainly being hit by the direct sunlight. Make the light cast shadowmaps, bias=0.1, size=256, smp.range=16 for soft shadows. The rendering should look quite like this:
Step 5 |	Clone yourself another attenuated bouncelight for the window showing the pale plue sky. The pale sky sheds quite some light into the room, so assign a multiplier value of 0.6, which is half of the sun's. Exclude the window from this light, but do include the rest of the scene. This light will make nice shadows: shadowmap bias 0.1, size=256, smp.range=32. Place the light somewhere in the middle of the window. As with all other bouncelights, do keep the "affect specular" switched off. This doesn't look too bad, don't you think?
Step 6 |	Now for next touch: light bouncing off the table. Once more add or clone an attenuated Omni, exclude only the table and give it the table's redish color. Beware and use this red table bouncelight very subtely, or it will tint your whole scene red quite strongly. Dim it down to a mutiplier of 0.2, that should be fine. Place the bouncelight onto the table and render. The rendering now looks like this:
Step 7 |	Okay, we are almost there. To further enhance our lighting we will add just a few more bouncelights accounting for the light that has been bounced around in the previous steps thus now being reflected off the ceiling and the remaining walls. Create a bouncelight for the ceiling. Same procedure as before, with this light having a white color. Thinking about it, one should perhaps dim down the multiplier value a bit, as the ceiling is reflecting only the small amount of light which has already been bounced around. But then again the ceiling has got a white color, which might make it more reflective than the walls. Consider this, when adjusting bounce- lights in your scenes. For the ceiling let's keep the bouncelights multiplier value at 0.3, cast shadowmaps bias=0.1, size=256, smp.range=32. So this is how it looks like now:
Step 8 |	The last bouncelight we are going to create is the one for the left wall. Yes, there still remain two walls which will have no bouncelight, but let's be lazy and not overdo it. Same cloning procedure as before, yellow wall color for the light, exclude wall, shadowmaps as before. As this is a secondary bounce- light we should dim it a bit down to multiplier 0.2. And here is the next rendering:
Final |	Here comes the final touch, the cream on top. Did you notice the windowframe being a bit dark? Our bouncelights mainly lit the inside of the room, but the windowframe, which actually sits in bright sunlight, didn't recieve much from this. So let's take care of the window. Make a copy of the sunlight, deactivate the shadowcasting and include the window only. Hit the renderbutton. Congratulations! You made it! Don't you think this looks good? For the full effect scroll back to the top of this tutorial and be horrified by the first rendering ;-) By the way, this is how the same scene is rendered with a true radiosity program like Lightscape: Well, our bouncelights do come close, don't they?
Thank you |	For your convenience you can download the lights created in this tutorial here: tut-lights.zip. This completes my tutorial on Natural Lighting. I hope you enjoyed reading it and found it useful, too. For questions or comments please e-mail me. tutorials@michaelscholz.de. (c) 2001 Michael Scholz www.michaelscholz.de