The light was flashing, giving two flashes in quick succession every ½ minute. The fog signal gave 3 blasts, low, low, high is quick succession every 1½ minutes. The building contractor was John Adams & Co of Glasgow. The optical apparatus was made by Chance Brothers and the lantern, parapet and revolving machine were made by Messrs Dove & Co. The fog signal machinery which cost £2,790 was made by Campbell Gas Engine Co. The lighthouse named Killantringan came into operation on 1 October 1900 and the light at Portpartick was discontinued. The name Killantringan is derived from Ringan, or Ninian's Cill of Cell.

It was not to be long before this light proved its worth. On 26 November 1900, the Principal Lightkeeper noticed a fishing boat in distress and fired a rocket to summon the lifeboat from Portpatrick, which took the crew off and towed the boat into the harbour.

There have been many incidents since then; the most recent being 26 February 1982 when the 800 ton container ship "Craigantlet" bound from Belfast to Liverpool ran aground on the rocks in Port-a-Maggie Bay, just below the lighthouse. The Principal Lightkeeper was the first person to raise the alarm. The crew was airlifted to safety by a Sea King from 819 Squadron at HMS Gannet, Prestwick. Because of the nature of her cargo, several containers were marked with hazard code numbers as they contained dangerous chemicals. Due to the danger of breaking up and spillage, the area was considered unsafe. An emergency unmanned light was in use during the 6½ weeks.

Some trouble was recently experienced with the roller bearing system and a new system of light was installed at Killantringan -a gearless pedestal with sealed beam lamp arrays.

The gearless pedestal used a low-voltage rotary mechanism which suited a wide range of power supplies, and the lamp units were light, which produced a good beam for a very low power input, and being sealed in a vacuum it did not deteriorate or tarnish. But the main advantage of the system was that it is almost fully automatic: the lightkeeper visited the lightroom hourly until 10pm, and then did not have to go near it until extinguishing time next morning, unless summoned by the alarm bell. The lamps are mass produced and so economical, and the apparatus convenient to install and maintain; and the cleaning of the lighthouse is much easier, with no lenses to polish and no machinery to oil.

The sealed beam lamp arrays look rather like rows of car headlights.