The city lights have accustomed us to the night's brightness, but they have also caused us to forget the profound depth of true darkness.

However, for sailors who have spent long periods at sea, the night is a reality they must confront. In the vast, open ocean, getting lost is dangerous and life-threatening.

To address this problem, humans built lighthouses, which became beacons of hope, guiding sailors safely forward. The existence of lighthouses has allowed countless ships to return home safely, and the evolution of lighthouses is a remarkable story of progress in light and technology.

The origin of lighthouses can be traced back to ancient times, but early lighthouses were quite primitive, and their lighting capabilities were far from satisfactory. At that time, lighthouses primarily relied on burning wood and charcoal. Not only were these fuels expensive, but they were also highly unstable.

In windy or rainy conditions, the braziers were easily extinguished, and ships often struggled to spot the faint light of the lighthouse from a distance. Especially on the vast sea, such early lighthouses were ineffective in providing reliable guidance, making nighttime navigation difficult and filled with uncertainty.

By the 17th century, coal began to replace wood as the primary fuel for lighthouses. Coal burned more steadily than wood, and its brightness was superior. To further improve the efficiency of coal combustion, bellows were installed in lighthouses to intensify the flame.

However, despite some progress in lighthouse lighting technology during this period, it remained challenging for sailors to see the light from a distance, particularly in poor weather conditions. The lighthouse's effectiveness in these situations was still limited.

A breakthrough came at the end of the 18th century when Swiss inventor Aimé Argand revolutionized lighthouse technology. He invented a new type of lighting device known as the "Argand lamp." This lamp featured a hollow wick and a glass chimney, making it four times brighter than traditional oil lamps.

This groundbreaking invention quickly gained recognition as the best available light source for lighthouses, marking a significant leap in lighthouse illumination. People soon realized that adding a reflector behind the light source could greatly enhance the light's brightness.

If the reflector was designed in an arc shape, the beam of light could be concentrated to its maximum extent and directed in one direction, thereby significantly improving the light's intensity and propagation distance.

In 1787, the Kinnaird Head Lighthouse installed 17 navigational lights, each consisting of Argand lamps and parabolic reflectors. The brightness of this lighthouse surpassed that of any previous lighthouse, making it one of the brightest lighthouses of its time.

This greatly enhanced the safety of nighttime navigation. However, even though the Argand lamp had dramatically improved lighthouse lighting, the quest for even greater brightness continued.

Scientists began to explore whether adding a convex lens in front of the light source could further focus the light and increase its intensity.

While this idea had great potential, it encountered several practical challenges. It was extremely difficult to manufacture a large convex lens suitable for a lighthouse, and the lens itself absorbed a significant amount of light.

As a result, instead of increasing the brightness, the convex lens diminished the effectiveness of the light's propagation. This issue frustrated scientists until the early 19th century when French physicist Augustin-Jean Fresnel developed a revolutionary solution.

Fresnel's research revealed that the refraction of light through a convex lens primarily occurred at the points where the light entered and exited the lens. Based on this discovery, Fresnel proposed designing the surface of the convex lens in a stepped pattern.

This design retained the curvature of the lens but significantly reduced its thickness. By doing so, the lens absorbed far less light while maintaining its focusing power. Furthermore, the weight of the Fresnel lens was drastically reduced, making it much easier to use in lighthouses.

In 1823, the Cordouan Lighthouse in France became the first to install a beacon light equipped with a Fresnel lens and a four-wick oil lamp. When the lighthouse was lit, its light pierced through the night sky, reaching dozens of nautical miles away, astonishing observers.

The lighthouse’s beam illuminated the waterways, providing a clear path through the darkness. The invention of the Fresnel lens was hailed as a milestone in the history of lighthouse technology, and it soon spread to lighthouses around the world.

The widespread adoption of this technology significantly enhanced the lighting capabilities of lighthouses and brought new levels of safety to maritime navigation.

The light from a lighthouse does more than just guide sailors safely on their journeys; it also represents humanity’s enduring pursuit of illumination and technological progress.

In this journey, the invention of the Fresnel lens stands out as one of the most important milestones. It transformed the lighthouse into a powerful beacon, forever changing the course of maritime history and laying a solid foundation for modern optical technology.