Types of Light Bulb Fittings: A Guide to Choosing the Right One

Understanding the various types of light bulb fittings is essential for anyone looking to replace or update their home or office lighting. Light bulb fittings, also known as caps or bases, are critical because they connect the bulb to the power supply and ensure it fits securely in the light fixture. There are numerous types of fittings, each of which corresponds with specific bulb types and fixtures.

Choosing the right light bulb fitting involves considering both the function of the light and the decor of the space it will illuminate. Different fittings also mean different bulb shapes and sizes, which can greatly affect the lighting and atmosphere of a room. Since each fitting type also offers its own set of benefits, being equipped with the right knowledge can not only brighten your space but also provide efficiency and longevity to your lighting solutions.

Key Takeaways

  • Light bulb fittings are integral to effectively connect your bulb to the power supply.
  • The right fitting corresponds to bulb type and lighting functionality for your space.
  • Understanding bulb shapes, sizes, and benefits ensures efficient and long-lasting lighting.

Types of Light Bulb Fittings


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When you’re choosing a new bulb, it’s crucial to select the right fitting to ensure compatibility with your light fixture.

Screw Bases

Edison Screw (ES) bases are common and named after Thomas Edison. The E27 is the standard size in Europe, while the E14, often referred to as Small Edison Screw (SES), is used for smaller lamps. Both E27 and E14 are part of the Edison screw cap family, which cater to varying bulb sizes but maintain a similar screw-in design.

Bayonet Bases

The Bayonet Cap (BC) or B22 fitting features two mounting pins and is widely used in the United Kingdom. You’ll find these in two sizes, the main B22d cap for general use and the Small Bayonet Cap (SBC) or B15d, suitable for smaller light fixtures. Bayonet cap bulbs are easily inserted with a push and twist action.

Pin Bases

Pin bases employ a ‘plug-in’ approach with two or more pins. Common types include G4, GU10, G9, GU5.3, and G4 caps for low-voltage halogen lamps, each corresponding to a specific distance between the pins, such as 4mm for G4. Bi-pin caps like GU4 and GY6.35 are found in various desk or spotlighting. Larger fluorescent tubes might use a bi-pin fitting like G13 for T8 tubes or G5 for T5 tubes.

Specialty Fittings

Beyond standard bases, there are specialty options like MR16 and MR11, which are multifaceted reflector bulbs usually seen in track lighting. Linear halogen lamps use the R7 base, and extra support for heavy-duty bulbs is offered by three-pin bases like T8, T10, and T12 caps.

Light Bulb Cap Types


Understanding the specific types of light bulb caps is essential for ensuring you select the right bulb for your fixtures. Each cap type has its own code, which is directly linked to its size and fitting mechanism.

Edison Screw Cap Types

Edison Screw (ES) caps are among the most common cap fittings you’ll find. They are characterized by their threaded metal base that screws into a compatible socket. The E27 cap, often referred to as the Standard Edison Screw (SES), is a widespread option with a 27mm diameter, fitting domestic and commercial light fixtures.

For smaller lamps or tighter spaces, you might require the E14 cap, also known as the Small Edison Screw (SES). This cap has a narrower 14mm diameter and is frequently used in decorative lighting, bedside lamps, and some appliances.

In instances where a larger fitting is required, you may come across the Giant Edison Screw (GES), which is larger than the standard ES cap.

Bayonet Cap Types

Bayonet Cap (BC) bulbs have a push-and-twist action that locks the bulb into place. The most common size you’ll encounter is the B22 or B22d cap, which has two mounting pins and a 22mm diameter. It’s a popular choice in the United Kingdom and other countries using similar standards.

If your fixture requires a smaller cap, look for the B15 or B15d, also known as Small Bayonet Cap (SBC) bulbs. These are perfect for smaller decorative fittings or more compact light fixtures. Their smaller base, with a 15mm diameter, still provides a secure and stable connection for the light bulb.

Choosing the Right Bulb Type


When selecting a light bulb for your home, you need to understand the various bulb type codes that correspond to different bulb shapes and energy efficiencies. It’s also important to compare LED, CFL, and halogen bulbs to determine which best fits your needs.

Understanding Bulb Type Codes

Bulb type codes identify the form factor and size of your light bulb. For example, A19 is a common bulb code you’ll come across, which means the bulb is part of the “A” series (arbitrary), has a pear-like shape, and its widest point measures 19 eighths of an inch in diameter. Understanding these codes helps you choose the right bulb that not only fits your fixtures but also delivers the ambiance and illumination you desire. Here’s a quick reference for some common bulb type codes:

  • A: Standard, pear-shaped bulbs commonly used in home lighting.
  • G: Globe-shaped bulbs used in vanity lighting or decorative applications.
  • PAR: Parabolic aluminized reflector bulbs used for directed, focused lighting.

With this knowledge, you can ensure compatibility and achieve the right lighting effect for your room.

Comparing LED, CFL, and Halogen Bulbs

When comparing bulb types, energy efficiency should be one of your top considerations. LED bulbs are at the forefront of energy-efficient lighting, offering a significant reduction in power consumption compared to traditional bulbs and remarkable longevity. As an example, LED bulbs can last more than two decades and provide similar light output to incandescent bulbs while using less energy.

On the other hand, CFLs (compact fluorescent light bulbs) are also energy-efficient and provide a longer life span than incandescent bulbs. However, they do contain a small amount of mercury, which requires careful disposal.

Halogen bulbs fall behind LED and CFL bulbs when it comes to energy efficiency, but they do offer bright, instant light and may be preferred in situations where accurate color rendering is essential. They are a type of incandescent bulb but operate at higher temperatures, resulting in improved efficiency over traditional incandescent bulbs.

Below is a high-level comparison:

Bulb Type Energy Efficiency Lifespan Mercury Content
LED Most Efficient Longest No
CFL More Efficient Long Yes
Halogen Better than Incandescent Shorter No

Choose the bulb type that aligns with your desire for energy savings, longevity, and environmental considerations.

Light Bulb Shapes and Uses


Light bulb shapes vary widely and are designed for specific functions and fixtures. Matching the right shape to your needs ensures optimal performance and aesthetics.

Spotlights and Reflector Bulbs

Spotlights—like the MR16 or MR11—are compact and directional light bulbs that produce a focused beam of light. These bulbs are ideal for accent lighting, highlighting artwork, or spotlighting in your kitchen. Reflector bulbs come in various shapes, including the multifaceted reflector (MR types) bulbs, commonly used in track lighting and recessed fixtures. The MR numbers reference the bulb’s diameter in eighths of an inch, so an MR16 is 2 inches in diameter.

Decorative Bulbs

For a touch of elegance, candle and candelabra bulbs are your go-to options. Their slim shape and soft light are perfect for chandeliers and wall sconces. If you’re working with a modern fixture or need a smaller bulb, capsule bulbs, including halogen capsules, provide bright light in a compact form. They’re often used in desk lamps and undercabinet lighting as they can fit into tight spaces without compromising on light output.

Sizing Light Bulbs and Fittings


When selecting the proper light bulb for your lamp or fixture, you must consider both the bulb’s diameter and the base size to ensure a perfect fit. Here’s how to measure and determine these crucial aspects.

Measuring Bulb Diameter

To find the diameter of your bulb, you’ll need to measure the bulb at its widest point. The diameter is typically expressed in eighths of an inch in the United States. For example, a bulb labeled as A19 has a diameter that is 19 eighths of an inch, or 19/8 inches, wide. For fixtures with reflectors such as spotlights or floodlights, the designation might be BR30, where 30 eighths of an inch (or 3 3/4 inches) is the diameter. Reference this light bulb sizes and shapes guide for a comprehensive look at different bulb shapes and their corresponding sizes to find the right fit for your lamp or fixture.

Determining the Correct Base Size

Light bulb bases are the bottom part of the bulb that screws or clicks into the fixture’s socket. The two primary base types are the Edison Screw (E) and the Bayonet Cap (B). The most common Edison Screw base sizes are E26 (standard medium base) and E12 (candelabra base), with the number indicating the diameter of the base in millimeters. For bayonet base bulbs, the standard sizes include B22d (bayonet double contact) and B15d (small bayonet), which are used in many domestic environments like ceiling and desk lamps. To identify the right base size, first check your fixture’s requirements, and then match them to the bulb’s base type and size. Familiarize yourself with different types of light bulb base sizes to ensure a secure fit.

The Benefits of Different Light Bulbs


When selecting light bulbs for your home or office, you’ll encounter a variety of types, each offering unique benefits. Understanding the advantages of each can help you make an informed decision tailored to your needs.

Energy Efficiency and Lifespan

LED Light Bulbs: You’ll find that LED bulbs are at the top of the list for energy efficiency. They use up to 90% less energy than traditional incandescent bulbs and can last up to 20 years or more with regular usage. This long lifespan means fewer replacements and less waste.

Fluorescent Light Bulbs: Fluorescent bulbs, known mainly as tubular CFLs, also offer enhanced energy efficiency. They typically use about 70% less energy than incandescent bulbs and often last about 10 times longer.

Light Quality and Color Rendering

Halogen Bulbs: Halogen lighting provides a crisp, bright light that closely mimics natural daylight. This can be particularly beneficial for tasks that require attention to detail and for settings that aim to emulate a daylight environment indoors.

Incandescent Bulbs: Warm and soothing, the light from incandescent bulbs is often favored for its color-rendering quality. Although less energy-efficient, they offer a full spectrum of color, ensuring objects appear true to their actual color under the light.

Installation and Replacement Guides

When you decide to tackle light bulb replacement on your own, a bit of knowledge can ensure a smooth process. These guides are your go-to resource for fitting a bulb correctly and choosing the ideal light bulb for your fixtures.


Step-by-Step Fitting Instructions

  1. Safety First: Always start by turning off the power at the circuit breaker or fuse box to prevent any electrical hazard.
  2. Remove the Old Bulb:
    • For bayonet mounts (like the common BC-B22d), gently push the bulb downward into the socket and turn counterclockwise.
    • For screw mounts (such as the Edison Screw caps), turn the bulb counterclockwise until it’s released from the socket.
  3. Install the New Bulb:
    • Line up the pins with the slots or PPT image for bayonet mounts and push gently, then twist clockwise to lock into place.
    • For screw mounts, place the new bulb into the socket and turn it clockwise until snug.

Choosing the Correct Bulb for Fixtures

  • Identify the Fitting Type: Check the old bulb or fixture for any markings indicating the fitting type, such as ‘BC-B22d’ for bayonet or ‘E27’ for Edison Screw.
  • Match the Bulb to the Fitting: A guide to light bulb sizes, types, shapes, and codes can greatly assist you in finding the right bulb. Ensure that the bulb’s base matches the light fitting type of your lamp or ceiling light.
  • Consider the Bulb’s Purpose: Determine whether you need a bulb for general lighting, task lighting, or mood lighting. This will influence the brightness and color temperature of the bulb you choose.

By following these detailed instructions and tips, you’ll confidently handle the installation and replacement of light bulbs around your home. Whether you’re working with ceiling lights or cozy bedside lamps, you’ve got this!

Safety Tips for Handling Bulbs

Before replacing or disposing of any bulbs, remember that each type has its own safety protocols to consider. These practices ensure that you handle bulbs properly, minimizing the risk of harm to you and the environment.

Handling and Disposing of Halogen and CFLs

Halogen bulbs can run at higher temperatures, so it’s important to let the bulb cool down completely before you attempt to remove it. Always grip the bulb lightly but firmly, and never apply force that could break the glass. When it comes to disposal, because Compact Fluorescent Lamps (CFLs) contain a small amount of mercury, they should never be thrown out with regular trash. Find your nearest lamp recycling site where they can be processed safely.

  • Halogen Bulbs:

    • Let cool before touching
    • Hold bulb firmly but gently
    • Do not use force
  • CFL Bulbs:

    • Dispose of at a recycling facility
    • Do not place in regular trash due to mercury content

Precautions with LED Bulbs

LED bulbs are more durable and typically run cooler than halogens and CFLs, but they should still be handled with care. Always turn off the power at the mains before replacing an LED bulb to prevent electric shock. Since LED bulbs often contain electronic components, they should also be disposed of at a recycling center. This helps reduce landfill waste and prevents potential damage to the environment due to improper disposal.

  • LED Bulbs:
    • Turn off power before replacement
    • Recycle properly to protect the environment

Common Questions About Light Bulbs

In this section, you’ll find clear answers to common queries you might have about light bulbs. From the true nature of different bulb types to the expected lifespan of each, we cut through the noise to provide you with the information you need.

Debunking Myths About Bulb Types

It’s easy to get confused with all the terms floating around. LED bulbs, CFL (Compact Fluorescent Lamps), and halogen bulbs may seem similar, but they have distinct characteristics. LED bulbs are highly energy-efficient, converting about 70% of their energy into light, which means they stay cooler than others. What sets them apart is their astonishing longevity and their ability to save on your electricity bills over time.

In contrast, CFLs are basically mini versions of full-sized fluorescents and are four times more efficient and longer-lasting than incandescent bulbs. However, they contain a small amount of mercury, which means you’ll need to handle them cautiously and recycle properly.

Halogen bulbs are a type of incandescent bulb and offer a crisp, white light. They are more efficient than traditional incandescent bulbs and have a longer lifespan but are outpaced by LEDs and CFLs in both aspects. Halogen bulbs tend to run hotter, which is a consideration for your lamp choices and use cases.

Understanding Light Bulb Lifespan

When you’re choosing a light bulb, you’re probably wondering how long it will last. This can help you gauge the value and the frequency of replacement.

  • LED bulbs have a remarkable lifespan. On average, they can last up to 25,000 hours—that’s years of use before you need to replace them.
  • CFLs shine for approximately 8,000 to 15,000 hours, so they also offer a substantial period of illumination before you need a new bulb.
  • Halogen bulbs glow for about 1,000 to 3,000 hours, which is longer than traditional incandescent bulbs but significantly shorter than LEDs or CFLs.

Resource List and Glossary

When you’re exploring lighting options, it helps to have a solid understanding of the different fittings and terms used. Below, you’ll find resources that elaborate on various light bulb fittings, as well as a glossary to demystify the jargon you might encounter.

Further Reading and Lighting Resources

For an in-depth look at light bulb types and fittings, check out these carefully curated resources:

  • Light Bulb Fittings Guide: This comprehensive guide provides clarity on the different types of light bulb fittings. It’s invaluable for when you need specifics on sizes and terminology.
  • Glossary of Lighting Terms: A fantastic resource for all the terms you might come across when dealing with light fittings is the A-Z Lighting Glossary. It covers terms from cap types to light bulb shapes and sizes.

Glossary of Terms

Here’s a quick reference table to help you understand common terms related to light bulb fittings:

Term Definition
Bayonet Cap (BC) A common connector type for light bulbs, where you insert and twist to lock into place.
Edison Screw (ES) A screw-type light bulb base used widely in many different types of lighting fixtures.
Lumens The measure of the total amount of visible light emitted by a source.
CFL Compact Fluorescent Lamp, a type of light bulb that uses fluorescent technology.
LED Light Emitting Diode, a highly efficient light bulb type that uses diodes to produce light.

Keep this glossary handy as you read through lighting guides and blog posts, and you’ll find it much easier to choose the right light bulb for your needs.