What are A21 Bulbs?
A-Shape ("Arbitrary") or general service bulbs are likely the light bulb we are all most familiar with. It's shape is so ubiquitous that this is likely the first form factor you think of when someone says "light bulb". A21 bulbs are slightly larger than A19 bulbs and typically come in outputs ranging from 75 watts up to 250 Watts in their incandescent forms.
Incandescent A-Shape Ban
Starting January 2012, 100 Watt incandescent A-Shape bulbs will not be available for sale in retail. This phase-out will continue and finish with 40 watt bulbs in January 2014.
A21 LED Replacements
Much of the progress made over the past few years has been focused on developing and perfecting the A19 LED. The opportunity is enormous with over 6 Billion bulbs in service worldwide. A21 LEDs are now commonly used for higher wattage replacements and are found in wattages typically ranging from 75 to 100 watt equals. The larger A21 size allows for more heat sink surface area and as such is a popular choice for manufacturers looking to build such higher wattage replacements.
SWITCH Lighting used the extra space afforded in the A21 form factor to introduce the SWITCH3-Way A21, the world's only LED Bulb that works with Three-Way switches.
Buyers purchasing A21 LED bulbs should be aware of the larger size of such bulbs and double check dimensions to ensure a proper fit.