<P> 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 . </P> <P> The most commonly used A-series light bulb type is the A19 bulb (or its metric equivalent, the A60 bulb), which is ⁄ in (2 ⁄ in; 60 mm) wide at its widest point and approximately 4 ⁄ 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 ⁄ in (1 ⁄ in; 48 mm) wide at its widest point . </P> <P> 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 . </P> <P> 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 . </P>

What is the difference between e26 and a19
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