Light Bulb Specifications Explained: A19, E26, Lumens, Watts, Kelvin & CRI

LafoHome Lighting Guide

What Do Light Bulb Specifications Actually Mean?

Quick answer: A light bulb specification tells you a different part of the bulb's performance or compatibility. E26 or E12 identifies the base, A19, ST19, G25 or B11 identifies the bulb shape, lumens measure brightness, watts measure power consumption, Kelvin (K) describes how warm or cool the light appears, and CRI describes how naturally colors appear.

If you're trying to understand the numbers and codes printed on a light bulb package, this guide explains what each one means—and which specifications actually matter when comparing LED bulbs.

What Specifications Should I Look for When Buying an LED Bulb?

Start with lumens, color temperature, CRI, dimming performance, bulb shape and base type. Lumens tell you how bright the bulb is, Kelvin tells you how warm or cool the light looks, and CRI indicates how naturally colors appear. Then make sure the bulb shape and base fit your fixture.

For many everyday residential spaces, a 2700K warm-white, CRI 90+, dimmable LED bulb is an excellent starting point. Choose the lumen output and bulb shape based on the room and fixture rather than buying by wattage alone.

TL;DR — Light Bulb Specifications at a Glance

The most important rule: don't judge an LED bulb by wattage alone. Check base → shape → lumens → Kelvin → CRI → dimming compatibility.

1. What Does E26 Mean on a Light Bulb?

E26 is the standard medium screw base used by many household light fixtures in the United States.

The “E” refers to the Edison screw design, while “26” refers approximately to the base diameter in millimeters.

E26 bases are commonly found in:

• Table lamps
• Floor lamps
• Pendant lights
• Ceiling fixtures
• Some chandeliers

What Does E12 Mean?

E12 is a smaller candelabra screw base commonly used in chandeliers, wall sconces and decorative fixtures.

Important: E12 and E26 describe the base, not the bulb shape.

Should I Buy an E12 or E26 Light Bulb?

Choose the base that matches your fixture socket. E26 is the common medium screw base used in many U.S. table lamps, floor lamps, pendants and ceiling fixtures. E12 is the smaller candelabra base commonly used in chandeliers, sconces and decorative fixtures.

Do not choose the base by bulb appearance alone. Bulb shapes such as A19, B11, G25 and ST19 describe the shape of the bulb, while E12 or E26 describes how the bulb connects to the fixture.

2. What Does A19 Mean?

A19 describes the shape and approximate size of a standard household bulb.

The “A” refers to the traditional A-series bulb shape, while “19” refers to the bulb's diameter measured in eighths of an inch. Nineteen eighths equals approximately 2⅜ inches.

A19 bulbs commonly use an E26 base in the United States.

Is A19 the Same as E26?

No. This is one of the most common light-bulb specification misunderstandings.

A19 = bulb shape.
E26 = bulb base.

A bulb can therefore be described as an A19 bulb with an E26 base.

3. What Do ST19, G25 and B11 Mean?

Like A19, these codes describe bulb shapes rather than brightness or color temperature.

The bulb shape matters especially when the bulb itself is visible. An exposed pendant or chandelier makes the bulb part of the fixture's design.

For a deeper comparison, see our Light Bulb Shapes & Sizes Guide.

4. What Are Lumens?

Lumens measure the amount of visible light produced by a bulb.

More lumens generally means more light output.

How Many Lumens Should I Buy?

For most everyday home lighting, about 800 lumens is a good starting point and is similar to the traditional brightness of a 60W incandescent bulb. Choose around 450 lumens for softer lamps, 1100 lumens for brighter general or task lighting, and 250–300 lumens when the bulb is mainly decorative or used for mood lighting.

Tip: Choose lumens based on the brightness you need—not watts. Watts tell you how much electricity the bulb uses.

5. Lumens vs Watts: What's the Difference?

Lumens measure light output. Watts measure electricity consumption.

This distinction is especially important with LEDs.

For example, an LED bulb consuming only 9 watts can produce around 800 lumens—similar to the light output historically associated with a 60-watt incandescent bulb.

Therefore:

Use lumens to compare brightness.
Use watts to compare energy consumption.

A label such as “60W equivalent” is a familiar brightness reference; it does not mean the LED actually consumes 60 watts.

6. What Does Kelvin Mean on a Light Bulb?

Kelvin (K) describes the color appearance of white light—not its brightness.

2700K vs 5000K: Which Light Bulb Should I Choose?

Choose 2700K warm white for living rooms, dining rooms, bedrooms, chandeliers and other spaces where you want a warm, comfortable atmosphere. Choose 5000K daylight for garages, workspaces, home offices and task-oriented areas where a crisp, brighter-looking light is preferred.

If the bulb itself is visible in a chandelier, pendant or decorative fixture, 2000K–2700K generally creates a warmer, more inviting appearance.

A 5000K bulb is not automatically brighter than a 2700K bulb. Two bulbs can have the same lumen output but very different color temperatures.

Read our complete Color Temperature Guide for a deeper comparison.

7. What Does CRI Mean?

CRI stands for Color Rendering Index. It describes how naturally colors appear under a light source compared with a reference source.

Higher color-rendering quality can be especially noticeable with skin tones, food, artwork, wood finishes, fabrics and interior décor.

LafoHome EcoBright clear-glass filament bulbs use CRI 90+ light to provide more natural-looking color in residential and decorative applications.

Is CRI 90+ Worth It?

CRI 90+ is a good choice when accurate, natural-looking colors matter. It is especially useful in dining rooms, kitchens, living spaces, chandeliers and decorative lighting, where food, furniture, wood tones, fabrics and skin tones should look natural.

For utility spaces where color quality is less important, CRI 80+ may be sufficient. For visible decorative lighting and rooms where appearance matters, CRI 90+ is generally the better choice.

8. What Does “Dimmable LED” Mean?

A dimmable LED bulb is designed to operate across a range of brightness levels when paired with a compatible dimmer.

However, a dimmable bulb does not guarantee perfect performance with every dimmer switch.

If LEDs flicker while dimming, the bulb itself is not always the cause. Dimmer compatibility and minimum electrical load can also matter.

See our guide: Why Do LED Lights Flicker?

9. What Does “Flicker-Free” Mean?

LEDs require electronic circuitry to convert household AC electricity into power the LEDs can use. Poor driver design or incompatible dimmers can cause visible fluctuations in light output.

For decorative and everyday home lighting, stable light output becomes particularly important when several bulbs are installed together in chandeliers, pendants or multi-bulb fixtures.

10. What Does Beam Angle Mean?

Beam angle describes how widely a bulb distributes its light.

A narrow beam concentrates light into a smaller area, while a wide beam spreads illumination more broadly.

Beam angle is especially important for spotlights, track lighting and directional lamps. Traditional clear-glass filament bulbs are generally designed for broad, room-filling illumination rather than a concentrated spotlight effect.

11. What Does Rated Life Mean?

Rated life is an estimate of how long a bulb is expected to operate under specified test conditions.

It should be treated as a performance benchmark rather than a guarantee that every bulb will operate for exactly that number of hours.

Actual life can be influenced by heat, fixture ventilation, switching frequency, dimmer compatibility and electrical conditions.

12. How Do You Read a Light Bulb Package?

Instead of looking at one specification, read the package in this order:

1. Base: Will it fit the socket?
2. Shape: Will it fit and look right in the fixture?
3. Lumens: Is it bright enough?
4. Kelvin: Do you want warm, neutral or daylight-colored light?
5. CRI: How important is natural-looking color?
6. Dimming: Will it work with your lighting controls?
7. Actual watts: How much electricity does it consume?
8. Rated life: What is its expected operating life?

In short: the best bulb isn't defined by one number. The specifications work together.

Common Light Bulb Specification Mistakes

• Buying by watts instead of lumens — watts measure energy, not brightness.
• Confusing A19 with E26 — A19 is the shape; E26 is the base.
• Assuming Kelvin means brightness — Kelvin describes color appearance.
• Ignoring physical bulb size — the correct base doesn't guarantee the bulb fits inside a shade.
• Ignoring CRI — two bulbs with similar lumens and Kelvin can render colors differently.
• Assuming every dimmable LED works with every dimmer — compatibility matters.

Which Specifications Matter Most?

If you're simply trying to buy the right bulb rather than decode its specifications, start with these six:

Base → Shape → Lumens → Kelvin → CRI → Dimming

Then consider decorative style, filament design, lifespan and other performance characteristics.

For a room-by-room buying process, use our complete guide to choosing the right light bulb.

LafoHome Specification Examples

Here are three examples showing how these specifications work together:

Explore LafoHome EcoBright LED filament bulbs or browse bulbs by A19 shape.

Frequently Asked Questions

What is the difference between A19 and E26?

A19 describes the bulb's shape and approximate dimensions. E26 describes the screw base. Many U.S. household bulbs are therefore A19 bulbs with E26 bases.

Does higher wattage mean a brighter LED bulb?

Not necessarily. For LEDs, compare lumens to determine light output. Watts tell you how much electrical power the bulb consumes.

Is 800 lumens bright?

About 800 lumens is a common level for everyday general lighting and is roughly associated with the traditional 60W incandescent brightness category.

Is 2700K brighter than 5000K?

No. Kelvin describes color appearance rather than light output. A 2700K and 5000K bulb can produce the same number of lumens.

Is CRI 90 good?

Yes. CRI 90+ generally provides very good color rendering and is especially useful where the appearance of food, skin, artwork, fabrics and interior finishes matters.

Can an E26 bulb fit an E12 socket?

No. E26 and E12 are different screw-base sizes and are not directly interchangeable.

What specifications should I check before buying an LED bulb?

Start with the socket base and physical bulb shape. Then compare lumens, Kelvin, CRI, dimmability, actual wattage and rated life.

Reviewed by LafoHome Lighting Specialists. Updated August 2026.