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An episode of "Genglubu: Charting the South China Sea", a China Global Television Network (CGTN) documentary series, offers a rare glimpse into the life of lighthouse keepers who climb reefs, brave typhoons and keep the lights shining across the South China Sea.

Among them is Zhou Liang, a lighthouse keeper from Sansha Navigation Aid Office in South China's Hainan Province. His job often requires him to stay on remote islands for months at a time to maintain these vital navigational aids.

"For sailors, seeing a lighthouse in the vast expanse of the ocean is like seeing hope," he said.

However, maintaining these lighthouses is not easy, as some stand on reefs surrounded by complex undercurrents. After typhoons, repair teams must reach them as soon as the sea allows.

"In summer and autumn, typhoons are frequent here. We must carry out inspections and maintenance after every typhoon," said Zhou Liang.

Hainan Province boasts a long history of lighthouses. Around its coastline stand 25 lighthouses, with some over 100 years old.

"Each lighthouse is basically located at an important angle, at a key position, mainly to help ships returning from the open sea use the lighthouses to determine their position," said Liu Huashun from Haikou Navigation Aid Office.

Today, new lighthouses stand in Xisha Qundao (the Xisha Islands) and Nansha Qundao (the Nansha Islands).

In the age of the Genglubu, a manual of sea routes created by Chinese fishermen more than 600 years ago, captains read the wind, the tide and the shape of reefs. Today, new systems keep watch.

"Today, relying on technologies such as BeiDou high-precision positioning, AIS remote telemetry and big data, we can track the movements of vessels navigating the South China Sea in real time. If a ship veers off course or gets too close to dangerous reefs, we can warn it in real time," said Zhou Jun from Sansha Navigation Aid Office.

"Imagine being surrounded by total darkness. Then, all of a sudden, you strike a match and watch the flame flare to life. I think that's what it feels like when a sailor suddenly spots a lighthouse in the darkness of the night," said Zhou Liang.