2-Pin vs 4-Pin CFL Lamps Explained

Compact fluorescent lamps (CFLs) have been a popular choice for energy efficient lighting in domestic, commercial and retail settings.  With a lot of these lamps having 2 pin and 4 pin options available this leads people to ask what the difference is between these two types of CFL lamps.  To offer a brief explanation it is because they are designed to work with two different types of electrical lighting systems even though they use the same type of fluorescent technology.

Understanding the difference between these two lamp types is important when you are choosing a replacement bulb.  If you choose the wrong type it is very unlikely that the lamp will work and you can damage the lighting fixture if you try to force the wrong type of lamp into the wrong fitting.  

What Are Compact Fluorescent Lamps?

Compact fluorescent lamps were made to replace traditional incandescent bulbs as a more energy efficient alternative.  CFL lamps generate light through a fluorescent process involving gas and phosphor coatings inside the lamp rather than using heat to generate the light.  This process means that CFL lamps can reduce the same amount of light for a lot less electricity - sometimes up to 80% less.  

Many CFL lamps are designed as plug-in lamps.  This means that they are made to fit into dedicated lighting fixtures rather than the standard screw or bayonet lamp holders. These CFL plug-in lamps normally have a 2-pin or 4-pin base made to fit into a particular type of lighting circuit and fixture. 

What Are 2-Pin CFL Lamps?

2-pin CFL lamps are plug-in compact fluorescent lamps that work with magnetic ballasts. They have two electrical contact pins on the base that will connect directly to the lamp holder.  They also include an internal starter that helps to initiate the electrical process that ignites the lamp.  As the start is within the lamp itself it does not require the ballast to perform this function.  When this type of lamp is switched on the magnetic ballast regulates the electrical current flowing through it leaving the starter within the lamp to start the ignition process. 

Common Uses of 2-Pin CFL Lamps

2-pin CFL lamps are generally used in older commercial lighting systems and fixtures that were designed specifically for magnetic ballasts.  You may find these systems in office ceiling lights; commercial downlights or corridor lighting.

2-Pin CFL Lamp Types

• PL-C lamps
• PL-S lamps
• PL-T lamps
• 2D lamps

It is worth noting that each of these types of lamp will be made for different applications.

What Are 4-Pin CFL Lamps?

4-pin CFL lamps have been made to operate with electronic ballasts instead of magnetic ballasts.  These lamps have four electrical contact pins on the base.  4-pin lamps will not have an internal starter meaning that they will rely on the electronic ballast for the ignition process and to regulate the current.   When you switch a 4-pin CFL lamp on the electronic ballast will supply the energy needed to ignite the lamp and will ensure the current travelling throughout the lamp is kept stable.

Common Applications for 4-Pin CFL Lamps

4-pin CFL lamps are more often found in more modern lighting systems that utilise electronic ballasts.   They can be found in commercial offices; retails lighting installations and modern commercial buildings to list just a few.  It is believed that electronic ballasts improve CFL lamp performance and will reduce flickering compared to magnetic ballast systems.

4-Pin CFL Lamp Types

• PL-L lamps
• PL-C lamps
• PL-T lamps
• 2D lamps

It is also worth noting that each of these types of lamp will be made for different applications.

How to Identify Whether You Need a 2-Pin or 4-Pin CFL Lamp

When you are replacing a compact fluorescent lamp it will be easiest to determine which lamp you need by looking at the base and counting the pins.  You should pay attention to their placement as some of these 2-pin and 4-pins lamps will have pins in slightly different arrangements.  

You can also check the model number which should be printed on the lamp or the packaging if you still have it.  This will usually indicate how many pins are required and what arrangement is needed.  Many retailers and manufacturers will use this part number on their website.

Why It’s Important to Choose the Correct Lamp

It is essential to use the correct CFL lamp type for your fitting for safe and reliable operation.  If you install the wrong lamp it is unlikely that it will work at all and it can damage the fitting in the process.  As we have also discussed above, if you manage to use a 2-pin lamp in a 4-pin  fixture it will not work correctly as it will not have been designed to work with the ballast within the fixture.

Are CFL Lamps Still Used Today?

CFL lamps are still being used in a number of commercial lighting installations despite the ever increasing popularity of LED lighting.  This is because many of these commercial settings will have installed these setups to specifically work with these CFL lamps and it would be costly to change the setup over for LED lighting.