The incident light metering method can be easily implemented using
radiosity as well. During the final gathering step a limited number of
scene patches should be replaced by auxiliary light metering
patches. These auxiliary patches are perfectly diffuse white patches
that are taken into account only during the final gathering step. In
this way their radiosity is proportional to the irradiance and these
radiosity values can be used for finding the scale factor. Of course,
auxiliary patches are not displayed in the final image, they are just
used to find the scale factor. Note that the predominantly used diffuse
radiosity method does not use radiance values, but radiosity, B, which
is 
times radiance. In this case the eq. (7.5) will be:
and the scale factor will be:
