What is a GLS Light Bulb?
The GLS (General Lighting Service) is the traditional type of light bulb that has been in use since the early twentieth century. It has the classic, pear-like bulb shape and its versatility means it is still one of the most popular types of lightbulb available today.
GLS bulbs are commonly fitted with either a B22d bayonet cap (sometimes abbreviated to BC), or an E27 Edison screw (ES) base. The B22d cap is the ‘push and twist’ type of fitting that is used on the majority of lamps in the UK, while the E27 is the screw-in type that is more common in Europe and the US.
These are not the only types of cap available. Read our guide to the different kind of lightbulbs here.
As GLS lightbulbs are so widespread, they are available in a variety of styles. Incandescent GLS bulbs, which have been used in homes for so long, will soon be banned in the UK under an EU directive that takes effect in September 2018. They will be replaced by energy-saving alternatives.
Types of GLS light bulb: (l-r) Incandescent GLS with BC-B22d bayonet base, halogen GLS with ES-E27 screw cap base, energy saving CFL (Compact Fluorescent) with a BC-B22d bayonet base and a clear glass LED filament GLS with ES-E27 screw cap base.
The CFL (Compact Fluorescent Lamp) light bulb was the early replacement for high-energy bulbs, but the GLS equivalent doesn’t look like a GLS at all. It is instead a narrow fluorescent tube that is turned into a compact shape (hence its name). It is designed to be a direct, energy-saving replacement for the GLS, so it is compatible with existing fittings, but it looks completely different.
LED GLS lightbulbs, however, have been designed to look like the incandescent bulbs they supersede. They have the classic pear shape and as the technology develops, they are beginning to look more like their traditional counterparts.
These will often be opaque (sometimes described as ‘pearl’ or ‘opal’) and they are made out of glass or a heat-resistant thermal plastic. Many have a white plastic base to hide the bulb’s componentry, but there are now models available that are completely transparent. Look out for the distinctive yellow ‘filaments’ of these LED lightbulbs, designed to mimic the filaments of the traditional incandescent GLS.