Glossary - Part E

•  Eclipse: A period when no light can be seen coming from a lighthouse optic.

•  Echelon Lens: A lens formed in steps (echelons) as in the original Fresnel dioptric bull’s-eye panel.

•  Element: An individual piece of glass in the lens assembly designed to intercept the light from the illuminant and project it outward toward the horizon or, in the case of a spherical reflector formed by catoptric elements, to return it to the illuminant, at the focus of the lens.

•  Emergency Light: A light of reduced intensity displayed by certain aids to navigation when the main light is extinguished.

•  Establish: To place an authorized aid to navigation in operation for the first time.

•  Extinguished: A lighted aid to navigation, which fails to show a light characteristic.