A light server is a full node with "LES server" option enabled. This option is disabled by default (at least as long as the LES implementation is still in experimental stage), so light clients actually DO need a somewhat "special" endpoint. Run
geth --lightserv 25
to allocate max. 25% of CPU resources for serving clients.
Peer discovery is also experimental, LES uses a PoC test version of the planned new RLPx v5 discovery protocol that allows searching specifically for a certain kind of nodes (light servers in our case). It takes a few minutes for the server to start advertising itself on the network.