The A-series light bulb is the "classic" type of light bulb that has been the most commonly used type for general-purpose lighting applications since the early 20th century. It has a pear-like shape and an Edison screw base. The number that follows the "A" within the A series indicates the width of the bulb in one-eighth inch units in North America or millimeters in India and Europe.
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Physical outline
The most commonly used A-series light bulb type is the A19 bulb (or its metric equivalent, the A60 bulb), which is 19/8 in (2 3/8 in; 60 mm) wide at its widest point and approximately 4 3/8 inches (110 mm) in length. Another common A-series light bulb type is the A15 bulb which is commonly used for appliances and ceiling fans. The A15 bulb is 15/8 in (1 7/8 in; 48 mm) wide at its widest point.
Socket type
Most A19 light bulbs come with an one-inch long Edison screw base, either of type E26 (i.e. 26 millimeters in diameter) in countries with a mains voltage of 100-120 volts, or of type E27 (i.e. 27 millimeters in diameter) in countries with 220-240 volts AC. A-series light bulbs using the older B22 bayonet twist type base are less common; they can be found in the UK and many British Commonwealth countries.
Specifications
ANSI C79.1-2002, IS 14897:2000, and JIS C 7710:1988 define the "A shape" as "a bulb shape having a spherical end section that is joined to the neck by a radius", where the radius is greater than that of the sphere, corresponds to a osculating circle outside the light bulb, and is tangent to both the neck and the sphere. The Energy Star certification only requires omnidirectional light bulbs to fit the overall dimensions of the corresponding ANSI bulb type.
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Lamp types
Although most A-series bulbs have historically used incandescent lighting technology, some other technologies - such as Compact Fluorescent (CFL) or LED lamps - have been used in A-series bulbs more recently.
Source of the article : Wikipedia
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