When the assembly line starts, the producer will check the incoming bulbs one by one, while the consumer will pack them (one bulb into each box). This flow repeats until the assembly line stops.
The following diagram is a graphical representation of this flow between the producer and the consumer:
We can consider the assembly line a helper of our factory, therefore it can be implemented as a helper or utility class (of course, it can be easily switched to a non-static implementation as well, so feel free to do the switch if it makes more sense for your cases):
public final class AssemblyLine ...