The first lighthouse was proposed in 1795 — the year in which a census of the Madras (now Chennai) city was taken.

The first lighthouse came up on the roof of the Exchange Building (present day Fort Museum) in 1796. Situated at 99 feet above sea level, the beam emanating from the 12 lamps fuelled by coconut oil swept the choppy waters of the sea as far as 25 miles from the shore. Merchants on the ship would exchange signals with the lighthouse and the transactions would later be conducted in the Public Exchange Hall downstairs, a lively meeting point for brokers, merchants and ships’ commanders.

This lighthouse functioned until 1841 when the British government erected a 120-ft Doric column in the High Court compound as a replacement that used argand lamps.

Source: http://en.wikipedia.org/wiki/Lighthouse,_Chennai#cite_note-Hindu_GlowingTaleOfLighthouses-5