Editing Fresnel lens (section)

=== Forerunners ===

The first person to focus a lighthouse beam using a lens was apparently the London glass-cutter Thomas Rogers, who proposed the idea to [[Trinity House]] in 1788.{{r|tag-prior}} The first Rogers lenses, 53{{nbsp}}cm in diameter and 14{{nbsp}}cm thick at the center, were installed at the [[Old Lower Lighthouse]] at [[Portland Bill]] in 1789. Behind each lamp was a back-coated spherical glass mirror, which reflected rear radiation back through the lamp and into the lens. Further samples were installed at [[Baily Lighthouse|Howth Baily]], [[North Foreland]], and at least four other locations by 1804. But much of the light was wasted by absorption in the glass.{{r|tag-prior}}<ref>Levitt, 2013, p.{{nbsp}}57.</ref>

In 1748, [[Georges-Louis Leclerc, Comte de Buffon]] was the first to replace a convex lens with a series of concentric [[Annulus (mathematics)|annular]] prisms, ground as steps in a single piece of glass,{{r|chisholm-1911-lighthouse}}to reduce weight and absorption. In 1790{{r|condorcet-1790}} (although secondary sources give the date as 1773{{r|appleton-1861|p=609}} or 1788{{r|tag-2017}}), the [[Marquis de Condorcet]] suggested that it would be easier to make the annular sections separately and assemble them on a frame; but even that was impractical at the time.{{r|tag-fres}}<ref name=levitt-p71>Levitt, 2013, p.{{nbsp}}71.</ref> These designs were intended not for lighthouses,{{r|chisholm-1911-lighthouse}} but for [[burning glass]]es.{{r|appleton-1861|p=609}} [[David Brewster]], however, proposed a system similar to Condorcet's in 1811,{{r|chisholm-1911-lighthouse|tag-2017|ripley-dana-1879}} and by 1820 was advocating its use in British lighthouses.{{r|chisholm-1911-brewster}}