Outdoor Lighting using Radiosity

Exterior Daylighting systems are quite easy to employ with knowledge of a few key components.  Although not intended to make you an expert on the topic, this guide will at the very least get you in the ballpark.  It is important to note that materials, object colors, and scale are all important factors.  Always use real scale and be mindful of working units when modeling.  If using object colors rather than materials, use subtle shades and avoid primary colors whenever possible. 

We first need to ensure that the renderer is set to the default scanline renderer.  This enables the Radiosity Advanced Lighting solution. 

Three components are necessary to properly light the geometry:  The lighting source, the Radiosity solution, and exposure control. 

The first step, of course, is to create the geometry you wish to light.  I will be using the Gwathmey experience for this example. 

1. Create the Daylighting system.  In the create panel, select Systems, then Daylight for the object type. 
   • Click and drag to create the "compass", then move the mouse and single-click for the light source's height.  It is important to note that the height does not actually have to be far away from the geometry, and placing it extremely far away will actually be detrimental. 
   • In the creation dialog, set the time of day, month, year, and location.  This will set the sun's position in the sky. 
   • Changing the north direction will rotate the solar path.  This is often preferred over rotating the geometry to orient correctly. 
     
     

     Once the daylight system is created, switch to the modify panel and switch the sunlight and skylight both to IES types.  Because Radiosity will be the advanced lighting solution, it is important to use IES lighting sources.    Also ensure that shadows are on and set to Ray Traced shadow types.  Ray traced shadows produce a hard, sharp, and accurate edge.    These are the only lighting settings required.

2. The next necessary component is to set up the Radiosity solution. 
   • Use the following settings. 

   • Use the default setting of 85% for the Initial Quality.  This does not control the "quality" of the scene, but rather the energy distribution.  Most of the energy is distributed in early iterations, which means there is a diminishing return for high quality settings here.  If the scene looks "noisy", however, increasing this value in small increments will sometimes improve the solution.    Set the refine iterations between 2 and 10.  2 is usually a good number for an outdoor scene.  This setting gathers energy on each face of the objects in the scene and averages it as a separate process form initial quality.  This prevents two adjacent faces from receiving a drastically different energy distribution.  The setting below it can be used for improving the quality of troublesome objects when the rest of the scene appears fine.   Under Interactive Tools section, set the filtering for indirect and direct light to 4 or lower.  "Noisy" shots or strange aberrations can often be prevented with a low setting here, but raising this setting above 4 tends to "wash out" or blur the image.  Think of this as a Gaussian blur on the Radiosity solution itself.    Possibly the most important area is in the Radiosity Meshing Parameters rollout.  The values here set the density of the Radiosity Solution's mesh, which consequently increases the quality of the ambient light solution.  On an outdoor lighting scene, however, there is not a great deal of ambient light variance.  In other words, set this value higher for outdoors and lower for indoors.  This directly affects the time it takes to calculate the solution, so only decrease this value as necessary or required.  A good setting for an outdoor scene is around 3' - 5'.    Leave all other settings at default.  This should produce a good solution.

3. Finally, set the exposure control.  Logarithmic exposure control uses the most accurate algorithms, but unfortunately tends to make highly saturated colors "bloom".  This can usually be fixed in photoshop via a saturation or levels adjustment. 
   • Ensure that the Exterior Daylight button is checked on.  Without this "clamp", the scene will be extremely washed out. 
   • You normally do not have to adjust brightness or contrast if everything else is set correctly. 

You must run the radiosity solution first, then render the scene.  The Radiosity solution is what bounces the light around in the scene and produces ambient light.  You can actually see the mesh if you turn on Edged Faces from the viewport context sensitive menu. 

Once the Radiosity Solution has been completed, render the scene. 

Brighter ground colors may lessen shadows because it bounces more light energy.  Radiosity picks up colors and transmits them when the energy bounces.  Note the difference in the solution when a green ground color is used. 

A darker grey ground color produces darker shade and shadow.

The Radiosity solution is valid until an object in the scene moves or changes.  In other words, the scene can be rotated freely without invalidating the Radiosity solution, so multiple angles can be rendered from one Radiosity run.