Glossary - Part I

•   Imitation Lighthouse: A reconstructed Lighthouse that attempts to express basic Lighthouse features but does not represent an individual historic Lighthouse.

•   Index of Refraction: A value that is found by dividing the speed of light in a vacuum by the speed of light in a second medium (such as glass).

•   Incandescent Oil Vapor (IOV) Lamp: A type of lamp in which oil was forced into a vaporizing chamber, and then into a mantle. Similar to the Coleman lamps, used in camping today.

•   Inner (or rear) Range Light: The light in a pair of range lights that is situated behind the other as viewed from the water.

•   Interim Light-keeper: A light-keeper who served on a temporary basis, usually between the appointments of full-time light-keepers.

•   Interrupted Quick Light: A quick flashing light in which the rapid alternations are interrupted at regular intervals by eclipses of long duration.

•   Isophase Light: A rhythmic light in which all durations of light and darkness are equal. (Formerly called equal interval light.)