It seems that lightning must be really intense or really close to show up well in the day, One must take into account that even in the daythe thick clouds of a storm block out a significant amount of light , enough to make strikes show up clearly and easily enough to make powerfull staticco and CG's. I still love lightning at night though, the colours and brilliant sheet lightning are defiantly superior to the daytime strikes, it also lights up the structure of the storms very well.
cheers mark