The quick answer is: The series connection produces more light. This can be determined with simple reasoning as follows:
(1) The current is fixed and
(2) Series connected elements have the same current through them
For the parallel connection, each bulb gets half the source current while, for the series connection, each bulb gets the full source current. Since power is proportional to the square of the current, each bulb in the parallel combination produces 1/4 the light of the bulbs in the series combination.
Also, if you understand that current is dual to voltage, resistance is dual to conductance, and parallel is dual to series, you can immediately get the answer by duality.
For example, consider the following:
When connected to a voltage source, two light bulbs in parallel produce 4 times as much light than two light bulbs in series.
Here's the dual:
When connected to a current source, two light bulbs in series produce 4 times as much light than two light bulb in parallel.
Since the first sentence is true, and since the second sentence is its dual, the second sentence is also true.