Quick answer: Choose a light bulb by matching four things in order: the base (E26 or E27 for most lamps, E12 for chandeliers, G9 or GU10 for small fixtures), a shape that fits your fixture, brightness in lumens — 800 lumens replaces a classic 60W bulb per ENERGY STAR — and a color temperature like 2700K–3000K for warm living spaces or 4000K–5000K for kitchens and work areas. Check dimmability and your fixture's max wattage marking before buying.
1. Match the base first — this is non-negotiable
Every bulb carries a letter-and-number base code: the letter names the connection type, the number the diameter in millimeters. No match, no install.
| Base | What it is | Where you'll find it |
|---|---|---|
| E26 | 26 mm Edison screw | Standard lamps and fixtures in North America, rated for 120V |
| E27 | 27 mm Edison screw | European, Asian and Oceanian fixtures, rated for 220–240V |
| E12 | 12 mm candelabra screw | Chandeliers, wall sconces, small decorative fixtures |
| E14 | 14 mm small Edison screw | Chandeliers, pendants and sconces, common in Europe |
| G9 | 9 mm bi-pin capsule | Small pendants, under-cabinet lights, compact fixtures |
| GU10 | Twist-and-lock pins | Track heads and recessed spotlights |
| G4 | 4 mm bi-pin capsule | Tiny decorative fixtures and display lighting |
One common question: can you swap E26 and E27? The threads are nearly identical, so they often fit each other's sockets — but the voltage ratings differ (120V vs 240V). The safest rule is simple: use the base and voltage your fixture was built for.
2. Pick a shape that fits — and flatters
Bulb shapes follow the same idea: the number is the diameter in eighths of an inch — an A19 is about 2.4 inches wide, a G25 globe about 3.1 inches.
| Shape | Look | Best for |
|---|---|---|
| A19 | Classic pear bulb | The default for table lamps, floor lamps and shaded fixtures |
| B10 / CA10 | Candle or bent-tip flame | Chandeliers and sconces where the bulb is visible |
| G25 | Globe | Bathroom vanities and pendants with exposed sockets |
| BR30 | Bulged reflector flood | Recessed ceiling cans |
| PAR20 / PAR30 / PAR38 | Parabolic spot or flood | Track lighting and outdoor security lights |
Shape matters for fit as well as looks: an oversized bulb may not seat fully in an enclosed fixture, and in a clear glass fixture the bulb becomes part of the décor — this is where globe and filament styles earn their keep. Fully enclosed fixtures need enclosed-rated bulbs, since trapped heat shortens LED life.
3. Think in lumens, not watts
Watts measure energy used; lumens measure light produced. Because LED bulbs sip power, a 9-watt LED can easily outshine a 60-watt incandescent — which is why the watt-equivalent on the box is only a rough guide.
| Old incandescent | Lumens needed | LED wattage range |
|---|---|---|
| 40W | 450 lm | 9–13W |
| 60W | 800 lm | 13–15W |
| 75W | 1,100 lm | 18–25W |
| 100W | 1,600 lm | 23–30W |
| 150W | 2,600 lm | 30–52W |
Pick your target lumens first, then choose the lowest-wattage bulb that delivers them — that is the most energy-efficient option.
4. Choose your color temperature
Lower Kelvin numbers read warm and golden; higher numbers read cool and crisp:
| Kelvin | Name | Where it works best |
|---|---|---|
| 2700K | Soft/warm white | Living rooms, bedrooms — closest to classic incandescent |
| 3000K | Warm white | Dining rooms, hallways, general home lighting |
| 3500K | Neutral white | Bathrooms, closets |
| 4100K | Cool white | Kitchens, laundry rooms |
| 5000K–6500K | Daylight | Garages, workshops, reading and detailed task work |
Two finer points worth the extra minute: CRI (Color Rendering Index) rates how truthfully light shows colors, on a scale of 100 — look for 80+ generally and 90+ where color matters, like kitchens, vanities and artwork. And keep the temperature consistent within a sightline: a 2700K lamp next to a 5000K ceiling light looks broken, not layered.
5. Dimming, lifespan and traps to avoid
Dimming: only dimmable LED bulbs belong on dimmer switches, and they work best with modern LED-compatible dimmers — an old dimmer can make LEDs flicker, buzz or fail early. Lifespan: LED bulbs typically last 15,000–50,000 hours compared with 750–2,000 for incandescent, so a bulb in a hard-to-reach fixture is exactly where LED pays off. Fixture wattage: respect the maximum wattage printed on the socket, which is a heat limit, not a brightness limit.
6. Our light bulb picks
- Amara Rain Glass Light Bulb — available in E26/E27 medium screw bases and dimmable, it is the straightforward upgrade for standard table and floor lamps.
- Alina Vale Glass Light Bulb — E12/E14 candelabra bases with dimming, sized for chandeliers and sconces where the bulb stays visible.
- Luma Glow Metal Light Bulb — G4/G9/GU10 pin bases in 3000K, 4000K or 6000K, dimmable, built for track heads, under-cabinet fixtures and small pendants.
- Alden Rain Glass Light Bulb — E14/E26/E27 bases with dimming, a flexible pick when you need one bulb that spans chandeliers, pendants and lamps.
Related Lighting Library guides
- Lumens, Kelvin, CRI and Wattage: A Simple Lighting Guide — the deeper explainer on every spec term in this article.
- Integrated LED vs Replaceable Bulb Fixtures: What to Choose — decide whether your next fixture should take bulbs at all.
- How to Choose a Chandelier — the fixtures where candelabra-base bulbs like E12 and B10 shapes matter most.
FAQ
Can I use an E27 bulb in an E26 socket?
They often fit each other's sockets, since the threads are nearly the same — but the voltage ratings differ (120V vs 240V). Match the bulb to your fixture's voltage and country instead.
How do I know what base my fixture takes?
Check the markings printed near the socket or inside the fixture — most list the base type and maximum wattage. If there are no markings, compare the socket to a known bulb or measure the screw diameter in millimeters: 26 mm is E26, 27 mm is E27, 12 mm is E12.
Will a dimmable LED work with my old dimmer switch?
Sometimes, but not reliably. Older dimmers were designed for incandescent loads and can cause LEDs to flicker, buzz or shut off at low levels. Pair dimmable LEDs with an LED-compatible dimmer for smooth, silent dimming.
Are LED bulbs worth it for hard-to-reach fixtures?
LED bulbs typically last 15,000–50,000 hours compared with 750–2,000 for incandescent — that is where the upgrade pays off fastest. Just make sure the bulb is rated for the fixture: enclosed or damp-rated housings need bulbs rated for those conditions.
What does CRI mean on a bulb box?
CRI (Color Rendering Index) scores how accurately light reveals colors, out of 100. Aim for 80+ in general and 90+ in kitchens, bathrooms and anywhere you do makeup, cooking or artwork — colors look noticeably more true.