How does the lighthouse work? by Gravastars

The mirror of the lighthouse isn't 'magic' per se, but rather a very specific manipulation of light.

Remember when Daniel first arrived to the island? He commented "the light here doesn't scatter right" which he then subsequently followed up with a bizarre experiment involving a time travelling payload. What this revealed is a kind of 'time bubble' encasing the island - what I believe to be the cause of the island's lighting problems.

Relating this to the lighthouse and we come full circle. What if you could bounce light in such a way, that it could reflect specific points of the globe within any specific period of time?

If Jacob is the man I think he is - the 'very clever man' who invented the series of equations which sent the Dharma initiative to the island, then I believe he is also capable of manufacturing such an intricate device. He invented the lighthouse to spy on the outside world; to construct a list of candidates to bring them to the island.