The GLS is the standard pear-shaped light bulb that everyone recognises, sometimes referred to as an A-shape or A60 light bulb. It stands for General Lighting Service, and has been in common use for decades. If you have a standard ceiling light in your home that needs a new bulb, chances are it uses a GLS bulb. As they are so common, GLS light bulbs are available with the two most widely used cap types: B22d bayonet cap (BC) and E27 Edison screw (ES). You can find all types of GLS bulbs, from the traditional incandescent GLS bulb that has been in use for a century, to cutting-edge, energy-saving LED bulbs.