Use assumed_gamma 1.0 and whatever is correct Display_Gamma
for your system in povray.ini. When removing the static ambient
light it is important to set gamma correctly so that radiosity
can produce correct ambient level. See
news://news.povray.org/39423CFE.5565DBF%40kivisalo.net
news://news.povray.org/39450341.610E8FC3%40kivisalo.net
K.K.
