I will also need to bias my random outputs so that I do not repeat the same strobe twice in a row.
Probably the easiest solution is to put your random-variable selection in a loop (probably a while() loop) and loop 'till the random next lamp is different from the current lamp.
i.e. Pick a random NextLamp number and if NextLamp == CurrentLamp, continue looping and get another random Next Lamp. If they are not equal (which will be true most of the time), break out of the loop. As long as this loop is running fast enough (relative to your flash interval), you can randomly pick the same number several times in a row and you'd never see a problem.
Of course when the time is up, CurrentLamp will be assigned the value of NextLamp and you'll have to find a new-random NextLamp.
Another way to do it is to make an array which excludes the CurrentLamp, and then pick a random element from the array. (Something like this is often done to simulate a deck of cards, where you can't select the same card again after it's removed from the deck.)