Since two ships passing are equally warned of the risk, the lighthouse is non-rival. Since it would be impossible to provide the lighthouse services only to those passing ships that paid for the service, the lighthouse is non-excludable. The other classic example of a public good is national security or national defense. The armed services provide security benefits to everyone who lives within the borders of a country. Also, once provided it is difficult to exclude non- payers.
Information has public good characteristics as well.
Indeed this is one reason for the slow start of electronic information services on the world wide web. Once information is placed onto a web site it can be accessed and used by millions of consumers almost simultaneously. Thus it is non-rivalrous. Also, it can be difficult to exclude non-paying customers from accessing the services. A standard assumption in general equilibrium models is that markets always clear.