Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A Fresnel lantern is a spotlight used in theatre, which employs a Fresnel lens to wash light over an area of the stage. The lens produces a wider, soft- edged beam of light, which is commonly used for back light and top light. The distinctive lens, named after Augustin-Jean Fresnel, has a 'stepped' appearance instead of the 'full' or 'smooth' appearance of other lenses. This allows the lens to have a much greater curvature than would otherwise be practical. The lens focuses the light by tilting each ring of glass slightly more towards the center as the distance is increased from the center of the lens. If the glass were completely flat, this would cause a corresponding pattern of circles of light, so Fresnel lenses are usually stippled on the flat side

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