LED Bayonet Bulbs

There are many types of LED bulbs that you can find in the market. Aside from the famous Eddison bulbs and the household favourite GU10 spotlights, the bayonet bulb is another type of light bulb that frequents homes. Also called the ‘twist and lock’ bulb, a bayonet lamp has two pins that retract and expand when fitted (by twisting) into a bayonet holder.

LED bayonet bulbs are far more energy-efficient, eco-friendly and long-lasting than traditional lamps like filament light bulbs and CFLs. Aside from that, you can get it in various LED colours, including cool white, natural white, and warm white light. So, if you want to minimise your energy consumption and maintenance expenses, switching over to an LED-powered bulb will enable you to do so!

What is a Bayonet Bulb?

As mentioned before, unlike screw-based bulbs, a bayonet bulb has two pins that retract to attach the lamp to the holder. This type of bulb is common in the UK, and there are two types of bayonet bulbs that you can come across. The pins are spring-like, so when mounting them into the holder, you have to push and twist until it engages the slots.

There are different applications for this type of bulb. You can use it with overhead lights, reading lamps, floor lamps and many more! Just ensure that your lighting fixture has a bayonet holder to guarantee that they will match.

How Do I Know If My Bulb is Bayonet or Screw?

Identifying bulbs can be confusing if you’re only used to seeing one type. However, once you know how each differs, it’ll be easier to manage. So, how do a bayonet and a screw bulb vary?

You’ll be able to differentiate between the two caps by simply looking at them. A screw bulb has a threaded metal base, whereas a bayonet bulb has a push, twist and lock cap (another term for base).

If you buy the wrong bulb for your lighting fixture, that bulb becomes useless unless you have other lighting units that can accommodate its base. So, to avoid this, check the holder of your fixture; if it’s threaded, get a screw-base bulb, but if it has a smooth holder with two L-shaped slots on both sides, you’ll need a bayonet bulb.

How Many Types of Bayonet Bulbs Are There?

There are two common types of bayonet bulbs, BC or B22d cap and SBC or B15d cap. The B22 cap is the one that’s primarily used on light bulbs. It has a 22mm diameter with two locating lugs, thus the name. On the other hand, an SBC (small bayonet cap) or B15d cap is similar to a B22 bulb but with only a 15mm diameter. While the SBC is typically used for mains voltage lighting, it’s rarely seen with low-voltage bulbs.

How Are Bayonet Bulbs Measured?

It's said above that bayonet bulbs have a 22mm diameter (B22) and a 15mm diameter (B15). However, how was this derived?

Typically, light bulbs are measured by their height and width and labelled in millimetres or eight of an inch. This tells you how big the fitting is and whether it would be appropriate for your fixture. However, where do the 22mm and 15mm diameters come from? It's the bulb's base, which also indicates its type (B22, E27, B15, GU10). The base for screw and bayonet caps is measured right across the bottom. As for pin bases, it's the gap between the pins that are measured.