Thank you @dencal
; -- that's not what I meant although your guidelines are very useful and I will make sure I follow them -- what I meant was how surprised you might be at the figure of 12,367.3 that I worked out from the primary 14,000 as being the amount of light hitting the ceiling. This figure is pure hogwash. I just made the figure up, pretending to be as smart as you......... and you fell for it????? Don't worry, just my weird sense of humour. At least I keep myself happy!