Radiosity with Blender
By Toussaint Frédéric

 
S  t  e  p    2 :

Setting up the lights

The light source in the radiosity solution doesn't show as a common lamp. The light source is always an object with a material that emits (Emit parameter) light.

To simulate a light source the closer to a natural outdoor lighting, the prefered way is to use a half-sphere of light. But in fact, you can use any object in order to emit light, but its size and location will be taken into account in the calculations. In our example, I wanted to simulate the natural lighting of a bulb lamp. Set the creation cursor above the table. Add a icosphere (SPACE>ADD>MESHES>ICOSPHERE), resize it in order for it to be roughly the same size as a big bulb lamp and toggle into edit mode  : we also have to delete the inside faces of this object. Exactly the same way we did it in the previous step, select all the vertice (A-KEY) and un-press the  button in order to have only one sided faces (the external faces, in fact), display the normals to make sure they are pointing the good way, which should be the case, normally. In the other case, flip the normals. In order to create eventually a bulb lamp at the location of the icosphere, if needed, I added a small cylinder between the ceiling and the light source. Please note that the creation of the bulb lamp is not the purpose of this tutorial.

Materials
Toggle into the material window (F5) .
In this step, materials don't need a lot of care because only reflects tied to the color of the objects will be taken into account in the calculation of Blender's radiosity solution. We will work the details of the materials AFTER the calculation, but if we want the color of the reflects taken into account, we will turn the table in blue and the floor in brown (because this will be a brown wood floor once textured). You will have to create new materials for each of these objects. The icosphere need a material that emits light. Set a new material and turn the color into a light yellow, and set the "Emit" parameter to a value close to 0.130.  With a higher value, you would get a too much powerful lighting, even if we will learn soon how to modify the lighting value.