Abstract: An inpavement light fixture for mounting in an airport runway or a taxiway having a cover with a flat surface and one or two windows for the passage of a light beam. An optical prism is detachably mounted in a cavity formed in the cover beside and beneath each window. The prism has three flat sides forming an equilateral triangle with two of the sides sloping upwardly to a top edge positioned at a top of its window. A special sealing member fits over the prism and preferably covers one of the two sides which slope upwardly. This member extends about a lower portion of the prism and forms a water tight seal. An electric light is mounted in a bottom receptacle on which the cover is supported. A light channel is formed in the top of the cover and extends from each window towards an edge of the cover. This channel has a bottom which slopes at a small angle to the flat top.