A Guide to Light Bulb Sizes, Shapes, Codes and Types

Introduction: Navigating the World of Light Bulbs

Are you looking to elevate the lighting design in your home but find the plethora of options overwhelming? Coordinating style and functionality while choosing the right light bulbs can be a daunting task. However, fear not! We’re here to provide you with an informative guide on light bulb sizes and types, helping you make informed decisions.

Decoding Light Bulb Labels

Understanding light bulb codes is crucial in your quest for the perfect illumination. These codes, typically found on the packaging, convey essential information about a bulb’s type and specifications. Let’s explore how to decipher these codes and find the ideal bulb for your fixtures.

Determining Light Bulb Size

Identifying the light bulb size is a straightforward process. The letters in the bulb code signify its shape and unique features, while the numbers indicate the base size, measured in eighths of an inch (⅛”). For instance, an A19 bulb tells us it has a standard household shape (code A), with ’19’ denoting a base size of 19/8ths of an inch. Similarly, A15 bulbs are smaller than A19 bulbs but share the same standard household light bulb base (E26).

Common light bulb shapes include:

A for Standard Household/Arbitrary
C for Candle
R for Reflector
MR for Multifaceted Reflector or Quartz Reflector Lamp
PAR for Parabolic Aluminized Reflector
G for Globe
T for Tubular

Understanding Light Bulb Bases

Light bulb bases come in various sizes, each identified by a unique code. These codes consist of a letter signifying the base’s shape and a number indicating its size. If you’re unsure about your bulb’s base compatibility, seek advice from a store associate to ensure a perfect fit.

Common Light Bulb Base Sizes

Standard-Medium, a regular sized screw in base: E26 or E27
Candelabra, a smaller screw in base: E12
Intermediate: E17
Bi-pin, a pin-in base with two points of contact: G4 or GU24
Twist-And-Lock base: GU10

Exploring Light Bulb Types

Light bulbs are available in four primary types: Light-Emitting Diode (LED), Compact Fluorescent (CFL), Incandescent, and Halogen. To simplify your selection process, consult our comprehensive light bulb size chart. Now, let’s delve into these types and the corresponding codes you’re likely to encounter.

Type A Light Bulbs

Bulbs within the A group find extensive use in standard household lighting. They are versatile, suitable for various fixtures, including hall lighting, ceiling fans, and more. Typically compatible with medium screw bases (E26 and E27) or the candelabra base (E12), the A19 bulb is the standard light bulb size. It’s worth noting that A19s are increasingly replaced with CFL Twists or Spirals due to improved energy efficiency.

CFLs feature a spiral-shaped design and are known for energy efficiency, emitting a soft glow while consuming minimal power. While budget-friendly, they may take some time to reach full brightness due to their design.

It’s essential to understand that while A19 and E26 bulbs may seem interchangeable, not all E26 bases are suitable for A19 bulb heads. Keep this distinction in mind during your light bulb shopping.

Type B and C Light Bulbs

Type B and C bulbs are elongated and have a tip resembling a candle flame, earning them the nickname “candle bulbs.” They are commonly used in decorative lighting fixtures like chandeliers, pendants, wall sconces, accent or pendant lights, and other decorative applications. Like A group bulbs, their most frequent base types include the E26 and E27 medium screw-in bases, the E12 candelabra base, and the E17 base.

Type BR Light Bulbs

The R and BR group includes reflectors and bulged reflectors, respectively. While not as common as A19 bulbs, you may encounter these bulbs in outdoor floodlights or recessed lighting. The BR30 and R20 bulbs are the most common in this category and typically feature E26 or E27 bases.

Type PAR Light Bulbs

PAR group bulbs are typically utilized for outdoor lighting, similar to BR lights. PAR stands for parabolic aluminized reflector, and these bulbs have higher wattage, providing ample illumination. The primary difference between PAR and BR lights lies in their focus—BR lights offer a broader wash of light, while PAR lights deliver more focused beams. The most common base types include the E26 and E27, as well as the G53 screw pin base.

Type MR Light Bulbs

MR group bulbs emit a concentrated, directionally focused beam of light and are available in various colors. Multifaceted reflector bulbs are popularly used in track lights, recessed lights, desks, and display cases. They typically utilize low-voltage wiring systems, making them ideal for landscaping applications like path and driveway lighting, gazebo lights, and paver lights. Among this group, the MR16 is commonly found in indoor settings due to its sleek style and spotlighting capabilities. The most common base types for MR bulbs within low-voltage AC/DC systems include the GX5.3 bi-pin or GZ4 bi-pin, while the GU10 bi-pin is suitable for 120-volt systems.

Type LFL and T Light Bulbs

T and LFL group lights refer to tubular and linear fluorescent lights, respectively, and encompass specialty and vintage options. Fluorescent comes in various light bulb sizes, with their type determined by both length and diameter. For instance, a T8 bulb has a one-inch (8/8 inch) diameter, while a T5 has a 5/8 inch diameter, and a T12 measures 12/8 inches (1.5 inches) in diameter. These fluorescent tube lights are available in different lengths and wattages.

T8 or T12 bulbs are commonly found in laundry rooms, kitchens, or garages. They often feature magnetic or electronic ballasts, which help regulate the flow of current in an electrical circuit. Typically, these fluorescent bulbs are energy-efficient, providing optimal brightness with a crisp, white glow that can last up to 20,000 hours. However, hybrid LED light bulb replacements have gained popularity due to their enhanced efficiency. T group lights commonly connect with E26 and E27 medium screw bases, E12 candelabra bases, E17 bases, BA15D bayonet bases, or the G13 bi-pin base.

Type G Light Bulbs

Lastly, the G group, also known as globe lights, is predominantly used for aesthetic purposes. You may recognize the G30 as the go-to choice for bathroom vanities. These bulbs often feature vintage styles, characterized by antique-looking filaments in the center, adding a touch of flair to any fixture. Dramatic or vintage globe bulbs are ideal for custom lighting designs in areas such as the den or dining room. G group lights most commonly connect with E26 and E27 medium screw bases and E12 candelabra bases.

Illuminating Your Space

With your newfound knowledge of light bulb sizes and types, you are well-equipped to make informed decisions when it comes to illuminating your home. Whether you’re enhancing the ambiance of your living room with a decorative chandelier or brightening your workspace with directional lighting, choosing the right light bulb can make all the difference. So, go ahead and explore the world of lighting options, and let your creativity shine through in every corner of your home.

an image showing different types of light bulbs

Conclusion: Lighting Up Your World

In this comprehensive guide to light bulb sizes and types, we’ve shed light on various aspects, from decoding codes to understanding light bulb sizes and types. Armed with this knowledge, you can confidently select the perfect light bulbs for your specific needs, whether it’s creating a cozy atmosphere, enhancing your decor, or improving energy efficiency.

Investing time in choosing the right light bulbs can truly transform your living spaces, making them more inviting, functional, and energy-efficient. So, don’t let the multitude of options overwhelm you. Instead, use this guide as your beacon to navigate the world of lighting, and let your home shine brightly.

Remember, the right light bulb is not just a source of illumination; it’s a reflection of your style and a key element in crafting the perfect atmosphere for your home.


  1. What do the letters and numbers on a light bulb code mean?
    • The letters indicate the bulb’s shape and features, while the numbers represent the base size, measured in eighths of an inch (⅛”).
  2. How do I identify my light bulb size?
    • The bulb’s size is determined by the numbers in its code, which indicate the base size based on the diameter at its widest point.
  3. What are the most common light bulb shapes and their uses?
    • Common shapes include A for standard household use, C for candle-like bulbs, R for reflectors, MR for multifaceted reflectors, PAR for outdoor lighting, G for globe-shaped bulbs, and T for tubular bulbs.
  4. What are the most common light bulb base sizes and their applications?
    • Common base sizes include E26 or E27 for standard-medium screw-in bases, E12 for candelabra bases, E17 for intermediate bases, G4 or GU24 for bi-pin bases, and GU10 for twist-and-lock bases.
  5. What are the four primary types of light bulbs, and what are their characteristics?
    • The four primary types are LED (energy-efficient and long-lasting), CFL (compact fluorescent, energy-saving), incandescent (traditional but less energy-efficient), and halogen (bright and instant-on).
  6. What is the difference between A19 and E26 bulbs?
    • A19 refers to the bulb’s shape, while E26 denotes the base size. A19 lamps and light fittings typically have an E26 base, but not all E26 bases must use A19 bulb heads.
  7. Are CFL bulbs a good replacement for A19 bulbs?
    • Yes, CFL Twists or Spirals are often used as replacements for A19 bulbs due to their improved energy efficiency.
  8. What are B and C type light bulbs, and where are they commonly used?
    • B and C bulbs are often called “candle bulbs” due to their elongated shape with a tip. They are typically used in decorative lighting fixtures such as chandeliers, pendants, and wall sconces.
  9. What are BR light bulbs, and where are they commonly used?
    • BR bulbs include reflectors and bulged reflectors and are often used as outdoor floodlights or in recessed lighting.
  10. What are PAR light bulbs, and how do they differ from BR bulbs?
    • PAR bulbs, or parabolic aluminized reflector bulbs, are also used for outdoor lighting but can provide more focused beams compared to BR bulbs.
  11. What are MR light bulbs, and where are they commonly used?
    • MR bulbs emit a concentrated beam of directionally focused light and are popular in track lights, recessed lights, and display cases.
  12. What are LFL and T type light bulbs, and where can I find them?
    • LFL and T bulbs refer to tubular and linear fluorescent lights, often used in laundry rooms, kitchens, garages, and various other settings.
  13. What are G type light bulbs, and how are they used?
    • G bulbs, or globe lights, are frequently used for aesthetic purposes and can add flair to fixtures in areas like bathrooms and dining rooms.
  14. Which light bulb type is the most energy-efficient?
    • LED bulbs are the most energy-efficient, consuming less electricity and lasting longer compared to other types.
  15. Are LED bulbs dimmable?
    • Many LED bulbs are dimmable, but it’s essential to check the packaging or product description to ensure compatibility with your dimmer switch.
  16. Are CFL bulbs still a good choice despite their slow warm-up time?
    • CFL bulbs are energy-efficient but may take a moment to reach full brightness. However, newer models are designed to light up more quickly.
  17. Can I use LED bulbs in fixtures designed for incandescent bulbs?
    • Yes, in most cases, LED bulbs are compatible with fixtures designed for incandescent bulbs.
  18. Are there LED replacements for T8 and T12 fluorescent tubes?
    • Yes, LED replacements for T8 and T12 fluorescent tubes are available and offer greater energy efficiency and longer lifespan.
  19. What are the benefits of using LED bulbs compared to traditional incandescent bulbs?
    • LED bulbs are more energy-efficient, have a longer lifespan, and produce less heat, making them a cost-effective and eco-friendly choice.
  20. Can I use a higher-wattage LED bulb in a fixture designed for lower wattage incandescent bulbs?
    • It’s generally safe to use a lower-wattage LED bulb in a fixture designed for higher wattage incandescent bulbs, but you should avoid exceeding the fixture’s recommended wattage.



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