Bulb Base Types (E27, E14, E40, GU10, MR16, G9, G13) and Kelvin–Lumen Selection Guide
IEC 60061 lamp cap dimensions and voltage rules (230 V E27/E14/GU10/G9 vs 12 V MR16/G4), LED lumen-to-watt equivalents, and 3000K–4000K–6500K CCT selection.
Choosing the right lamp base and LED bulb requires verifying both mechanical cap geometry and operating voltage (direct 230 V AC mains vs 12 V AC/DC driver). Under IEC 60061, the prefix letter identifies the cap mechanism (E = Edison screw, G / GU = bi-pin, B = bayonet) while the number specifies thread outer diameter or pin center-to-center spacing in millimeters (`mm`).
> Related Category: Browse lamp holders and compatible LED families in Lamp Holders, LED Bulbs, and Bulbs.
IEC 60061 lamp base dimensions and 12 V vs 230 V rules
A frequent field error is confusing 50 mm reflector spotlights (230 V GU10 vs 12 V MR16/GU5.3) or miniature capsules (230 V G9 vs 12 V G4):
| Cap code | Mechanism & dimension | Operating voltage | Typical luminaire / lamp family |
|---|---|---|---|
| E27 | Standard Edison screw, Ø27 mm | 230 V AC | Residential/office ceiling fixtures, wall sconces, A60/globe LEDs |
| E14 | Small Edison screw (SES), Ø14 mm | 230 V AC | Chandeliers, table lamps & LED candle bulbs |
| E40 | Goliath Edison screw, Ø40 mm | 230 V AC | High-bay warehouse, street & high-wattage industrial LED lamps |
| GU10 | Twist-lock mushroom bi-pin, 10 mm | 230 V AC | Mains-voltage 50 mm recessed/surface downlights (no external driver) |
| GU5.3 (MR16) | Push-fit slender bi-pin, 5.3 mm | 12 V AC/DC | Bathroom Zone 1/2 SELV downlights (requires 12 V driver) |
| G9 | Looped/flat bi-pin, 9 mm | 230 V AC | Glass-globe pendants & mains LED capsule bulbs |
| G4 | Fine miniature bi-pin, 4 mm | 12 V DC/AC | Cabinet, marine/RV & decorative low-voltage capsules |
| G13 / G5 | Double-ended bi-pin, 13 mm (T8) / 5 mm (T5) | 230 V AC (ballast-bypass LED) | Batten fixtures & fluorescent / LED tube lamps |
LED tube (G13) retrofit note: When retrofitting legacy magnetic/electronic fluorescent battens to direct-mains LED tubes, bypass the ballast and verify whether the LED tube is single-ended powered (`L` and `N` wired strictly to the marked input cap) or double-ended powered. For 12 V MR16 and G4 drivers, apply the 20–25% headroom rule in our LED Strip & 12 V/24 V Power Supply Sizing Guide.
Lumens vs Watts: LED brightness equivalency chart
Watts (`W`) measure electrical power draw, whereas Lumens (`lm`) measure total visible light output:
| Legacy incandescent | CFL equivalent | Modern LED power | Luminous flux (Lumens) |
|---|---|---|---|
| 25 W | 5 – 6 W | 3 – 4 W | 250 – 350 lm (multi-arm chandeliers, accent) |
| 40 W | 8 – 9 W | 5 – 6 W | 450 – 550 lm (hallways, bedside lamps) |
| 60 W | 11 – 13 W | 8 – 9.5 W | 800 – 860 lm (standard bedrooms & rooms) |
| 75 W | 15 – 18 W | 11 – 12 W | 1050 – 1200 lm (kitchens, home offices) |
| 100 W | 20 – 23 W | 14 – 16 W | 1500 – 1650 lm (large living areas, retail) |
Choosing Kelvin (CCT) color temperature
- 2700 K – 3200 K (Warm White): Relaxing amber-warm tone suited for bedrooms, living rooms, restaurants, and hospitality spaces.
- 4000 K (Neutral / Natural White): Clean balanced white (especially with CRI ≥80–90) ideal for kitchens, vanity mirrors, offices, classrooms, and retail displays.
- 6500 K (Cool Daylight): Crisp high-contrast bluish white preferred in workshops, garages, warehouses, and inspection benches.
Frequently asked questions
Can a 50 mm MR16 downlight be converted to GU10?
Yes. Because both MR16 and GU10 lamps share a 50 mm reflector bezel diameter, you can remove the 12 V transformer and replace the push-pin GU5.3 socket with a ceramic GU10 mains lamp holder wired to 230 V AC (provided bathroom IP/SELV zone rules permit 230 V).
When are ceramic (porcelain) lamp holders necessary?
Use ceramic E27/E40/GU10 lamp holders inside enclosed glass globes, high-wattage industrial lamps, oven/hood environments, and outdoor fixtures where heat ages thermoplastic holders.
Can any LED bulb be used on a wall dimmer?
No. Non-dimmable LED drivers flicker or fail on phase-cut dimmers; always pair explicitly marked Dimmable LED bulbs with trailing-edge LED dimmers.
What happens if 230 V AC is applied directly to a G4 or GU5.3 LED bulb?
A 12 V G4 or MR16/GU5.3 lamp connected directly to 230 V AC will suffer immediate catastrophic driver failure and trip the circuit breaker.