A popular lamp used in striplights and floodlights, and ranging in wattage from 20W-1500W. Below posed by ship on 11/28/07: BR = R-Lamp with Par Like Shape, (Squat test Reflecting area and Lens, Seemingly Widest Beam Angle) Binary Reflector ER = R-Type Lamp Shape With Longest Elliptical Reflector Shape, Seemingly Narrowest Beam Angle. An incandescent lamp with an elliptically-shaped reflector. This shape produces a focal point directly in front of the lamp which reduces light absorption in some types of luminaries. It is particularly effective at increasing the efficiency of baffled downlights. K = Milk Bottle/Beer Bottle Shaped Bulb. (Arbitrary Designation)/Narrow focus Directional Reflector. PAR = Parabolic Aluminized Reflector Par lamps rely on both the internal reflector and prisms in the lens for the control of the light beam. R = R-Lamp Reflector Spotlight, Blown Glass Globe Shaped Reflector and Lens, Very Rounded. R-57/R-60 = BR or R lamp shape with coned/nipple top instead of rounded. RP = R-Type lamp with a Parabolic Reflector and more straight angular sides and sharper angles. Bow Shape Lamp, Sharp arc like angles, all sides with approx. the same arc & angle. For more information, see this thread.