### 4.1.1 Introduction

Radiosity is a lighting technique to simulate the diffuse exchange of radiation between the objects of a scene. With a raytracer like POV-Ray, normally only the direct influence of light sources on the objects can be calculated, all shadowed parts look totally flat. Radiosity can help to overcome this limitation. More details on the technical aspects can be found in the reference section.

To enable radiosity, you have to add a radiosity block to the global_settings in your POV-Ray scene file. Radiosity is more accurate than simplistic ambient light but it takes much longer to compute, so it can be usefull to switch off radiosity during scene development. You can use a declared constant or an INI-file constant and an `#if` statement to do this:

      #declare RAD = off;

      global_settings {
         #if(RAD)
            radiosity {
               ...
            }
         #end
      }

Most important for radiosity are the ambient and diffuse finish components of the objects. Their effect differs quite much from a conventionally lit scene.

- `ambient`: specifies the amount of light emitted by the object. This is the basis for radiosity without conventional lighting but also in scenes with light sources this can be important. Since most materials do not actually emit light, the default value of `0.1` is too high in most cases. You can also change ambient_light to influence this.
- `diffuse`: influences the amount of diffuse reflection of incoming light. In a radiosity scene this does not only mean the direct appearance of the surface but also how much other objects are illuminated by indirect light from this surface.