u could use the gi_joe script
or
make a poly sphere put normals to face inwards.
create an ambient light with intensity 0
give the psphere a lambert wiv clay colour and turn up the ambient quite high and slightly raise the incandesence
tweak the ambience and incadense to get what u want
go render globals chose mental ray and turn on final gather to bout 500 and put on raytracing

render and twea settings to u get what u want
this is how i do it but there r other ways (i alos use this and the gi_joes script)

hope this helps