It is simply a binary counter.
each bulb is a bit in your counter.
1 bulb, 1 bit, 2 states. 0 or 1
2 bulbs, 2 bits, 4 states. 00 01 10 11
3 bulbs, 3 bits, 8 states. 000 001 010 011 100 101 110 111
etc..
You then increment the counter with a clock circuit or some other trigger source.
The...