The real reason why I would replace all the lamps after the first one or
two
failed is that it's easier to get the ladder etc. out once, rather than do
it over and over as the lamps fail.

N


That's a reason too, but generally once two fail completely, they've all
been very dim for quite a while. It's hard to notice until you see a new one
side by side, then you realize the reason for the eyestrain. Unfortunatly
all too many people still operate discharge lamps with an incandescent
mentality, that if it still lights up it's good.