Shat-R-Shield high intensity discharge (HID) lamps are designed to be safely used in open fixtures and are excellent for lighting large areas. In addition to offering greater flexibility in system design, open fixtures are less expensive and more compact than enclosed fixtures. the lenses on enclosed fixtures can reduce light output by up to 10% (compounded over time by the build-up of dirt, insects and other debris on the lens). these lamps are the most efficient source of high intensity light and are also available in non-cycling versions. their efficiency is up to 140 lumens per watt and the light produced is a warm golden color. because of their yellow light output, they are frequently used in street lighting and other areas where color rendering is not critical. Although they are not quite as energy efficient, metal halide is generally used when pure white light is needed.