This structure, designed by the engineer John Smeaton, was also the first to employ the classic curved hyperbolic design. Following the success of Smeaton's innovations, a large number of lighthouses were built on the open sea. Interlocking masonry blocks remained the principal material of lighthouse construction until they were replaced by concrete and steel in the 20th century. There are now three major kinds of offshore lighthouse structures. The second utilizes a concrete base that sinks to the bottom of the water, thus anchoring the lighthouse tower that rises from this base.
Most lighthouses also have landing pads for helicopters.
The most common type is the electric-filament lamp, which requires as much as 1.5 kilowatts to as little as 5 watts in small buoys. Refinements in lenses and reflectors have made it possible for a 250-watt bulb to be boosted to several hundred thousand candlepower, or candelas. Sirens and horns are commonly used to provide audible warnings when a lighthouse and its beacon are obscured by bad weather. But because the range of their sound is also highly dependent on weather conditions, many lighthouses are also fitted with radio and radar beacons, which either amplify a ship's radar or emit signals of their own that can be detected by navigators. Radio and satellite-based navigation systems have greatly reduced the need for large lighthouses in sighting land, although smaller structures are still important aids to navigating crowded coastal waters and shipping lanes.