Light Bulb Specifications Explained: Bases, Shapes, Lumens, CRI, LED Types & More

Buying a light bulb can feel more complicated than it should. A package may show codes such as E26, E12, A19 or ST19, followed by lumens, watts, Kelvin, CRI, beam angle and rated life. Each number answers a different question.

This guide helps you compare the specifications that matter most, avoid common buying mistakes, and choose the right light for your fixture and room.

Light Bulb Specifications at a Glance

1. Light Bulb Bases: E12 vs. E26 vs. GU10

The base is the first specification to check because it determines whether the bulb can physically and electrically connect to the fixture. Bulbs with different bases are not directly interchangeable.

LafoHome options: EcoBright B11 E12 candelabra bulbs and EcoBright E26 household bulbs.

2. Bulb Shapes: A19 vs. ST19 vs. G25 vs. B11

Shape affects more than appearance. It can determine whether a bulb fits inside a shade, whether the filament is visible, and how naturally the bulb complements the fixture.

Read our detailed Light Bulb Shapes and Sizes Guide for additional dimensions and fixture examples.

3. Lumens vs. Watts: Brightness and Energy Use

Lumens measure visible light. Watts measure electricity use. With modern LEDs, you should compare lumens—not watts—when deciding how bright a bulb will be.

4. Color Temperature: 2000K to 5000K

Color temperature is measured in Kelvin. Lower values appear more amber and relaxing, while higher values appear whiter and more energizing. Kelvin does not measure brightness.

5. CRI 70 vs. 80 vs. 90+

CRI, or Color Rendering Index, describes how naturally a light source reveals colors compared with a reference source. The closer the score is to 100, the more accurately colors generally appear.

LafoHome EcoBright LED filament bulbs feature CRI 90+ light for natural-looking residential illumination.

6. Dimmability and LED Dimmer Compatibility

A dimmable bulb can reduce its light output, but the bulb and dimmer need to work together. An older incandescent dimmer may not provide stable performance with a small LED load.

7. Incandescent vs. Halogen vs. CFL vs. LED

Lighting technology influences efficiency, heat, visual appearance, startup behavior and lifespan. For most household applications, LED now offers the strongest overall combination of efficiency and versatility.

SMD LED vs. LED Filament

SMD LEDs mount chips on a circuit board, often behind a diffuser. They are highly versatile and work well for high-output, directional and smart-lighting designs. LED filament bulbs arrange many tiny LEDs along slender strips that resemble traditional filaments. They are especially attractive in clear-glass fixtures and can distribute light broadly around the bulb.

8. Beam Angle: Spot, Flood or Omnidirectional Light

Beam angle describes the width of the main light cone. A narrow angle concentrates light on a small target. A wider angle spreads light over a larger area.

A19, ST19, G25 and B11 filament bulbs are normally selected for broad general light and decorative appearance, rather than a tightly controlled spotlight beam.

9. Rated Lifespan: What Does 15,000 Hours Mean?

Rated life is an estimate based on testing—not a promise that every bulb will fail at one exact hour. Heat, airflow, voltage quality, switching, dimmer compatibility and enclosed fixtures can all affect real-world life.

10. Other Specifications to Check

11. Eight-Step Light Bulb Buying Checklist

1. Match the base: E12, E26, GU10 or another socket type.
2. Confirm dimensions: Check height and diameter, not just the shape name.
3. Choose lumens: Compare visible light output rather than wattage alone.
4. Select Kelvin: Choose warmer light for comfort or cooler light for visual clarity.
5. Check CRI: Choose CRI 90+ where natural color matters.
6. Confirm dimmability: Pair dimmable LEDs with a compatible LED dimmer.
7. Review fixture conditions: Enclosed, damp, wet or low-voltage installations need extra attention.
8. Compare lifespan and warranty: Consider long-term value, not price alone.

12. Which LafoHome Bulb Should I Choose?

Frequently Asked Questions

What is the most common light bulb base in the United States?

E26 is the most common medium screw base for household lamps, pendants and ceiling fixtures. E12 is the smaller candelabra base commonly used in chandeliers and sconces.

What is the difference between A19 and E26?

A19 describes the bulb's shape and approximate diameter. E26 describes the screw-base size. A standard household bulb is often labeled A19 E26 because it combines both specifications.

What is the difference between E12 and E26?

E12 has a small 12 mm screw base, while E26 has a medium 26 mm screw base. They do not fit the same socket without an adapter, and an adapter may not be appropriate for every fixture.

Do higher watts mean a brighter LED bulb?

Not necessarily. Watts measure energy use. Lumens measure visible light output. Use lumens when comparing brightness.

How many lumens replace a 60W incandescent bulb?

About 800 lumens is a common 60W-equivalent benchmark, although exact output varies by manufacturer and product.

Is 1100 lumens the same as a traditional 100W incandescent bulb?

It is a bright replacement category, but the traditional benchmark for a full 100W incandescent is often closer to 1600 lumens. Always compare the actual lumen number, not the equivalent-watt claim alone.

Is CRI 90 better than CRI 80?

CRI 90 generally renders colors more accurately than CRI 80. The difference is especially useful for skin tones, food, wood, artwork and colorful interiors.

Which color temperature is best for a living room?

Many households prefer 2700K warm white because it feels comfortable and inviting. A 2000K bulb is much more amber and is better used for decorative ambience.

Which color temperature is best for a home office?

Some people prefer 4000K to 5000K for a crisp, focused environment. Others prefer 2700K or 3000K if the office shares space with a living area.

Why does my LED bulb flicker when dimmed?

Common causes include an incompatible dimmer, an older dimmer designed for higher incandescent loads, insufficient minimum load or a bulb-driver compatibility issue.

Are LED filament bulbs only decorative?

No. LED filament bulbs range from low-output amber mood lights to brighter general-purpose bulbs. Check lumens, Kelvin and CRI to understand the intended application.

What bulb shape is best for a bathroom vanity?

G25 globe bulbs are a popular choice because their round form looks balanced around a mirror. High CRI is helpful for skin tones, grooming and makeup.

What bulb shape is best for a chandelier?

B11, BA11 and CA11 candle-shaped bulbs are designed to complement chandeliers and decorative sconces. Confirm whether the fixture requires an E12 or E26 base.

Can I use a higher-watt-equivalent LED in my fixture?

Check the LED's actual wattage against the fixture's maximum wattage and confirm that the bulb is physically suitable for the enclosure. Equivalent wattage is only a brightness comparison.

How long does a 15,000-hour LED bulb last?

At three hours per day, 15,000 hours equals approximately 13.7 years in theory. Real-world life varies with heat, fixture design, switching, voltage and dimmer compatibility.

Installation note: Product and fixture requirements vary. Always check the product page, package instructions, fixture label and dimmer manufacturer's compatibility information before installation.