 Some lamps have the tube bent into a circle, used for table lamps or other places where a more compact light source is desired.Larger U-shaped lamps are used to provide the same amount of light in a more compact area, and are used for special architectural purposes.Compact fluorescent lamps have several small-diameter tubes joined in a bundle of two, four, or six, or a small diameter tube coiled into a helix, to provide a high amount of light output in little volume.