Last year we had a long period when the picture on our BV11 would suddenly dim. Sometimes just once, then sometimes several times in sequence. Nick at B&O Wilmslow suggested that it might be a problem with the light sensor module, and to try partial covering of the sensor (prism on top of TV). This seemed to make little difference other than to lower the picture brightness.
I feared that something serious might be wrong with the TV. Then suddenly, the dimming problem went away and normal service resumed. Has anyone else had a similar problem?