The lighthouse stands on the cliff two kilometres north of the village of Pendeen, on a headland called Pendeen Watch. It is within the Aire Point to Carrick Du Site of Special Scientific Interest, the Cornwall Area of Outstanding Natural Beauty, and the Penwith Heritage Coast. The South West Coast Path runs past its southern wall. Trinity House lit the optic for the first time on 3 October 1900. Until then ships coming round the corner from St Ives Bay had to read the geography in fog and breaking swell, and many did not read it well enough. The wrecks of The Liberty below the lighthouse and the Alacrity along the nearby beach are the wrong sort of monuments. The light was meant to make such monuments rarer.

Attached to the tower is a low E-shaped block split into four cottages. Three housed the resident keepers, their wives, and their children; the fourth was the duty office and the supernumerary keeper's bunk. Water came off the flat roof of the accommodation block, drained into an underground tank, and was carried in by the family. A separate engine house held the fog horn machinery - a 12-inch siren whose deep boom rolled out across the sea in poor visibility. Pendeen's engine house is, today, the only example in Britain to have kept its original 12-inch siren and associated machinery in place. The cottages are holiday lets now. The Atlantic comes through the kitchen windows in winter all the same.

The first lamp was a five-wick Argand burner, made by Chance Brothers of Smethwick near Birmingham - the great Victorian glass and lighthouse engineering firm that supplied half the world's lenses. In 1906 it gave way to a vapour burner with a range of 20 nautical miles. In 1922 Pendeen was among the first lighthouses fitted with a 75mm Hood incandescent oil burner; the new mantle lamp pushed the visible range out to nearly 28 nautical miles. Then came electricity. The current came from dynamos run off semi-diesel engines housed in the same engine room, with the Gardners replaced by Ruston & Hornsby diesels in 1963. The lamp was a 3.5-kilowatt Osram gas-filled bulb, specially built for Trinity House by the General Electric Company. There was even a self-changing turntable: if the lamp failed, an alarm sounded and a reserve bulb rotated into the focus; if that failed, a self-lighting acetylene lamp took over.

On 3 May 1995, the keepers walked out of Pendeen Watch for the final time and the station was automated. The clockwork that had turned the great lens was already gone - replaced by electric motors in 1963 - and now everything else followed. The 3.5-kilowatt filament lamps gave way to 35-watt metal-halide lamps on an automatic changer. Batteries did the work that the engine-house diesels and the keepers had once done together. A lighthouse that had needed three families to live on its cliff was now a building that mostly ran itself, watched from a Trinity House operations centre many miles away. The cottages went over to holiday lettings; the engine house, its 12-inch siren and machinery still in place, was preserved. The fog horn was silenced in 2013, after a public consultation, on the grounds that modern shipping no longer needed it.

In 2025, after 119 years of doing the same job, the revolving fresnel lens assembly was lifted out of Pendeen tower during Trinity House modernisation works. Trinity House had been removing mercury from its lighthouses across England for years - the metal vapour was now classed as a workplace hazard, and the alternatives finally existed. The 1906 lens was preserved and loaned to the Korea National Lighthouse Museum; a new LED lantern unit, self-contained and modest, took its place. The flash characteristic is unchanged: white, every fifteen seconds, visible far out into the approaches to the Bristol Channel. Climb the South West Coast Path on a clear evening and you can still see the same beam sweeping out over the same cliff. Down at Pendeen, fishermen still call it the Watch. Whatever sits inside the optic, the job is the one Trinity House described in October 1900: to make sure no ship comes onto these rocks for want of a light.