8+ Light Bulb Shapes and Code Meanings

Light bulbs come in a variety of shapes and sizes, each with their own unique code and meaning. Understanding light bulb codes can help you choose the right bulb for your lighting needs. Here are 8+ common light bulb shapes and their code meanings explained:

A-Shape Bulbs

A-shape bulbs, also known as pear-shaped or “standard” light bulbs, are the most common household light bulb shape. They have a rounded top and taper down to a narrower bottom.


  • A15 – Smaller standard home bulb with a 15/8 inch (38mm) diameter. Used for appliances and decorative fixtures.
  • A19 – Standard household light bulb with a 19/8 inch (60mm) diameter. The most common bulb.
  • A21 – Larger standard bulb with a 21/8 inch (53mm) diameter. Used for brighter task lighting.
  • A23 – Extra large standard bulb with a 23/8 inch (60mm) diameter. Provides maximum light output.

A-shape bulbs are omnidirectional, meaning they cast light in all directions. They are suitable for table lamps, overhead fixtures, and more. Common types of A-shape bulbs include incandescent, LED, halogen, and CFL.

Globe Bulbs

Globe bulbs have a round, globe-like shape. They cast light evenly in all directions, producing a soft ambient glow.


  • G16.5 – Smaller globe bulb with a 16.5/8 inch (42mm) diameter.
  • G25 – Standard globe bulb with a 25/8 inch (64mm) diameter. The most common size.
  • G30 – Larger globe bulb with a 30/8 inch (76mm) diameter, providing more light output.
  • G40 – Extra large globe bulb with a 40/8 inch (102mm) diameter. Used for maximum light levels.

Globe bulbs work well in pendant lights, chandeliers, vanity lights, and exposed bulb fixtures. Popular globe bulb types include LED, incandescent and CFL.

Reflector (R) Bulbs

Reflector bulbs have an internal reflective coating that directs light forward in a narrow beam. This makes them ideal for directional lighting such as recessed cans and track lighting.


  • BR30 – Common 65mm reflector bulb equivalent to a 50W BR30 incandescent.
  • BR40 – Larger 84mm reflector bulb equivalent to a 65W BR40 incandescent. Provides increased light output.
  • R14 – Mini 50mm reflector bulb for smaller directional fixtures.
  • R20 – Standard 79mm reflector bulb equivalent to a 50W PAR20 halogen.

Reflector bulbs come in a range of beam spreads from spot (narrow) to flood (wide). LED and incandescent are the most common options.

Candelabra Bulbs

Candelabra bulbs have a small profile and pointed tip, designed to fit in chandeliers and decorative fixtures with candle-like sockets. They are smaller than standard A-shape bulbs.


  • E12 – The common candelabra base with a 12mm diameter.
  • E17 – A mini candelabra base with a 17mm diameter, used for smaller chandeliers.

Popular candelabra bulbs include 60W equivalent LED, 40W incandescent, and 7W CFL types. Their pointed shape helps direct light downwards.

Flame Tip Bulbs

Flame tip bulbs have a tapered, flame-shaped tip that mimics the look of a candle flame. They provide accent lighting in chandeliers and wall sconces.


  • T4 – Mini flame tip bulb with a 4mm diameter base. Provides a delicate flame effect.
  • T6 – Small flame tip bulb with a 6mm diameter base, common in chandeliers.
  • T8 – Standard flame tip bulb with an 8mm diameter base.

These decorative bulbs have a distinct, elegant look. LED and incandescent types are available.

Tube Bulbs

Tube bulbs have a long tubular shape and come in straight and u-shaped varieties. They provide uniform, widespread lighting.


  • T5 – Slim 5/8 inch (16mm) diameter straight tube bulb, commonly used for undercabinet lighting.
  • T8 – 1 inch (25mm) diameter straight tube bulb, the general standard for fluorescent tubes.
  • T12 – Wider 1 1/2 inch (38mm) straight fluorescent tube bulb that provides more light.
  • T2, T3, T4 – Miniature U-shaped tube bulbs used decoratively in fixtures.

Fluorescent and LED are the most popular technology options for tube bulbs.

Candle Bulbs

Candle bulbs resemble a candle flame with a rounded top and cylindrical profile. They give a warm, vintage look.


  • B10 – Shorter 1 1/4 inch (32mm) diameter candle bulb.
  • B11 – Taller 2 inch (51mm) diameter candle bulb provides more light.

These stylish bulbs work well in chandeliers and sconces. Incandescent and LED types are common.

Spiral CFL Bulbs

Spiral CFLs have a twisted spiral shape that provides 360° lighting coverage. The compact spiral design allows them to fit in tighter spaces.


  • 2D – Mini 9 watt spiral CFL bulb equivalent to a 40 watt incandescent.
  • 4D – 18 watt spiral CFL equivalent to a 75 watt incandescent. Common for table lamps.
  • 5D, 6D, 7D – Larger 26, 32, and 42 watt spiral CFLs available for increased brightness.

With their efficient fluorescent technology, spiral CFLs work well in table lamps, fixtures, and more. The spiral shape distributes light in all directions.

Specialty Bulb Shapes

Beyond common household bulbs, there are many specialty and decorative bulb shapes for unique lighting applications:

  • Flamed Arrow Bulb: Arrowhead-shaped filament inside a rounded bulb.
  • Torpedo Bulb: Elongated with pointed ends, used in railroad signal lighting.
  • Mogul Base: Larger bulbs for track lighting and industrial fixtures.
  • Capsule Bulb: Ovoid shape for modern, exposed bulb fixtures.
  • Blob Bulb: Round shape with a unique melted look.
  • Lotus Bulb: Petal-shaped lines encircling an inner filament.
  • Silhouette Bulb: Profile-shaped bulbs for artistic fixtures.

Specialty bulbs allow creative applications for modern, artistic, and vintage lighting looks.

Light Bulb Buying Tips

Follow these tips when purchasing bulbs to ensure you get the right product:

  • Match the bulb shape and base to your lighting fixture. This is crucial for correct fit and function.
  • Check the lumens rating instead of watts to understand brightness. Lumens indicate actual light output.
  • Consider light color. Bulbs come in warm white, cool white, daylight, and soft white shades. Light color impacts ambiance.
  • Choose the correct beam spread if using a reflector bulb. Narrow spotlights or wide floodlights have different applications.
  • Calculate the lifespan in years from the lifespan in hours. LEDs can last decades based on average use.
  • Understand bulb dimmability if using a dimmer switch. Not all bulbs can be dimmed.
  • Buy from reputable brands for quality and safety. Avoid non-compliant cheap bulbs.

Following light bulb shape codes along with these tips will ensure you get the right bulbs for each lighting purpose in your home.

Frequently Asked Questions About Light Bulb Shapes and Codes

What do light bulb codes like A19 and BR30 mean?

Light bulb codes like A19 and BR30 refer to the shape, size, and type of the bulb. The letters indicate shape (A = Arbitrary, R = Reflector, etc) while the numbers reference the diameter in eighths of an inch. So A19 is an arbitrary/standard shape with a 19/8″ (2 3/8″) diameter. BR30 is a 65mm reflector bulb.

How do I determine what bulb shape I need?

Look at the existing light bulb you are replacing and match the shape, size, base style and diameter as closely as possible. Also check any markings on the light fixture socket and user manuals. Taking the old bulb with you to the store can also help ensure you get the right replacement.

What’s the difference between incandescent and LED bulbs?

Incandescent bulbs produce light by heating a filament, making them inefficient but providing a warm, natural light. LED bulbs are energy efficient and long lasting, but emit a cooler, more clinical light. Newer LEDs mimic incandescent qualities for the best of both technologies.

How do I choose the right wattage bulb?

Focus on lumens not watts. Lumens indicate the actual brightness of the bulb. Choose a bulb with similar or slightly lower lumens than the existing bulb you are replacing for the best light output. Generally lower watts use less energy for the same lumens.

Where should I use globe bulbs vs. standard A-shape bulbs?

Globe bulbs provide dispersed, ambient lighting since the light shines in all directions. They work best in open fixtures like chandeliers and pendant lights. A-shape bulbs direct light downwards so are ideal for table lamps, overhead fixtures, and recessed lighting.

What are G9 halogen bulbs used for?

G9 halogen bulbs have a small pin base and compact capsule shape, making them ideal for directional lighting in confined spaces such as track lighting, undercabinet lights and mini recessed cans where a brighter, focused beam is needed.

Why are there so many spiral CFL bulb shapes and sizes?

The spiral shape allows compact fluorescent (CFL) bulbs to fold up into compact shapes that can fit into tight spaces and fixtures designed for incandescent bulbs. The spiral CFLs come in many diameters, lengths and sizes to properly fit different lamp bases.

When should I choose R20 bulbs vs BR20 bulbs?

BR20 bulbs have a reflective coating to direct light forward in a spot beam pattern. R20 bulbs simply refer to the R shape and 20/8″ diameter, emitting an omnidirectional light pattern. If focused lighting is needed, choose BR20. For general ambient lighting, R20 works well.

Can I use a three-way bulb in a regular socket?

Yes, you can use a three-way bulb in a regular socket. The bulb will simply function as a normal one-brightness bulb. The third contact point will not connect to anything. The advantage is that three-way bulbs allow you to convert a regular socket to a three-way socket later if needed.


Understanding light bulb shape codes and meanings allows you to choose the ideal bulbs for your home lighting. Now that you know the common bulb types and terminology, you can shop with confidence and install bulbs that provide the perfect lighting ambiance and function. Following the tips above will ensure you get the right A-shape, globe, reflector or specialty bulb for table lamps, chandeliers, recessed lighting and more. Knowing how to decode bulb shape codes gives you the knowledge to upgrade your home lighting for maximum brightness, efficiency and style.