Thanks, BB (or should I say BF for the moment? )... you got me on both points. My logic on the calculations was flawed, although as soon as you corrected me, I realised what a numpty I was being. And yes, I know that with recessed lights such as this, there wouldn't be any actual light spill from the fittings onto the ceiling - it would be all GI that lit the ceiling. But that's why I was so confused about the ceiling dome. Yes, I had shadows set (as you can tell by the shadows in various places on the wall) and since all the lights in the scene are point lights, they must all be raytraced shadows, so I also had raytracing on. so where the illumination for the dome is coming from is beyond me.

As regards the colour of the ceiling... looking at the texture map, it's meant to be a creamy kind of colour, similar to the walls and the dome that you can see in my images. So not sure why it's coming out the colour it is in my versions. And yes, I'm also sure that all the lights present are in the correct place - I made all parts of the room invisible apart from the light fittings, and then used orthogrpahic views to place the lights correctly. So I do'nt know why some lights seem to be interacting with the ceiling more brightly than others.

'Tis a mystery, as they say.

JonTheCelt