Incandescent light bulbs are made in a great variety of shapes and sizes. The most basic shape has been designated with the letter A and is the familiar pear shape one might buy for home use. However, there are many commercial and industrial uses for A bulbs because of their universal practicality. The number following the A, such as 15, 19, 21, or 23 refers to the size. Specialty A bulbs include the A21 which is a large bulb, just over five inches in length. The A15 bulb is smaller, most commonly known as an appliance bulb. These bulbs may be clear for maximum illumination or frosted for a softer light. Some have a silvered bowl to reduce glare. Bulbs for rough service have extra filament supports and are excellent for drop cords or for places subject to vibrations. Linear incandescent bulbs look similar to long fluorescent bulbs, but they plug into a special fixture with two side prongs and range in length from about two feet to a meter. These lights enhance skin tones and are most often used in bathroom and have a long filament, which is fragile. Tubular bulbs have a standard screw base at one end and they are often used in signs, display cases, chandeliers and for track lighting.
Standard sizes of incandescent light bulbs include all the A bulbs. The A19 is the most familiar four-inch size and will fit almost any standard light fixture. The A23 has a longer neck with an overall length of more than six inches. These often work for historical renovations where the fixtures are designed for larger bulbs. A bulbs usually have the standard medium screw base and sometimes a narrow candelabra base. PS sizes are also pear shaped and include bulbs with medium and large mogul bases. Mogul bases can support two or three-way wattages from PS25, PS30, PS35, PS40 to PS52. The lengths increase from six inches to thirteen inches and may be as bright as 1000 watts. As length increases, so does the diameter, and a PS52 may have a diameter of 6.5 inches. Many of these bulbs are available in yellow, which attracts fewer bugs than white light, and pink for a warmer glow. The wide variety of these bulbs has been developed to meet the range of needs for commercial lighting.