Quick answer: E27 is a large screw base, E14 is a smaller screw base, B22 uses side pins with a push-and-turn connection, and GU10 uses two short twist-lock pins underneath. Match the base code, operating voltage and fitting requirements before ordering. Shape alone does not establish compatibility.
Buying a replacement light bulb should be straightforward. Yet many customers know the wattage and colour they want without knowing whether their fitting requires an E27, B22, E14 or GU10 base. That detail determines whether the globe will fit.
An E27 bulb cannot be installed in a B22 holder. An E14 bulb may look similar to an E27, but its screw base is considerably smaller. A GU10 spotlight may resemble an MR16 lamp from the front while using a different connection and supply arrangement.
Match the new bulb’s base code to the existing bulb or lamp holder before comparing wattage, lumens or colour temperature.
Quick comparison: E27, B22, E14 and GU10
| Base | Common name | How it connects | Typical applications |
|---|---|---|---|
| E27 | Edison screw | Screws into the holder | Pendants, table lamps, ceiling and wall fittings |
| B22 | Bayonet cap | Pushes in and turns to lock | Household ceiling fittings and general-purpose lamps |
| E14 | Small Edison screw | Screws into a smaller holder | Chandeliers, candle fittings and compact lamps |
| GU10 | Twist-lock spotlight base | Pushes in and twists to lock | Compatible downlights, spotlights and directional fittings |
What does a light bulb base do?
The base, or cap, is the section that connects the globe to its holder. It holds the lamp in position and makes the electrical connection. A mechanically matching base is only one part of compatibility: voltage, dimensions and the fitting’s operating requirements still matter.
The base is separate from shape, brightness and lighting technology. For example, standard A60 lamps, decorative filament globes, G125 globes and some reflector lamps can all use E27 bases. Two A60 bulbs can look similar while one has an E27 connection and the other has B22. Never identify a replacement by shape alone.
What is an E27 bulb?
E27 is an Edison screw base with an approximate diameter of 27mm. It screws clockwise into a compatible threaded holder. E27 is commonly found in pendants, table and floor lamps, ceiling fittings, wall lights and decorative exposed-bulb fittings.
How to identify E27
- Look for a relatively wide metal screw thread.
- Check for “E27” on the bulb, packaging or fitting.
- Do not confuse it with the narrower E14 screw base.
Decorative G45, ST64, G95 and G125 globes may use E27, but confirm the individual product specification rather than relying on shape.
Choosing an E27 replacement
Browse screw-in bulbs and check the E27 base specification. This collection also includes other screw-base sizes, so confirm E27 on the product you choose.
Compare an opal lamp for diffused light with a clear filament lamp where the bulb forms part of the visual design. Then check light output, colour temperature, overall size and dimming requirements.
What is a B22 bulb?
B22 is a bayonet-style base with two small pins projecting from opposite sides of its cap. A compatible holder uses a push-and-turn locking action rather than a screw thread. The number refers to an approximate cap diameter of 22mm.
You may see “B22d” in technical information. Check the complete designation and the fitting requirements when choosing a replacement.
How to identify B22
- Two pins on opposite sides of the cap.
- A smooth metal body without a screw thread.
- For common B22d lamps, two separate contacts underneath.
- A B22 or B22d marking and a matching bayonet holder.
Customers sometimes call B22 “clip-in” or “pin-type”, but bayonet is the clearer term. It is used in many household ceiling fittings, pendant holders, table lamps and utility lights.
Choosing a B22 replacement
Browse bulbs and globes and check for a B22 base. The collection contains multiple connection types. Confirm the product’s base, voltage, dimensions, light output and colour before ordering.
E27 vs B22: which one do you need?
Neither base is inherently better. Choose the type required by the existing holder: E27 for a compatible threaded holder, or B22 for a compatible bayonet holder. They are not directly interchangeable.
An adaptor adds length and may affect clearance, heat management and mechanical support. Do not assume an adaptor makes an otherwise unsuitable lamp safe for the fitting. Buying the correct base is usually the simpler route.
What is an E14 bulb?
E14 is a small Edison screw base with an approximate diameter of 14mm. It is also called SES, or small Edison screw. It is commonly used in chandeliers, decorative wall lights, bedside lamps and compact fittings.
How to identify E14
- A narrow threaded metal base, smaller than E27.
- “E14” or “SES” on the bulb, packaging or fitting.
- Often a candle, golf-ball, pygmy or reflector shape, although shape alone is not proof.
E14 is a connection type, not a guarantee that a lamp is suitable for an appliance. Ovens and other specialist applications require lamps rated for their operating conditions.
Choosing an E14 replacement
Compare screw-in bulbs and check for E14 compatibility. Check that the selected product is E14 rather than E27 or E40. For a chandelier, confirm bulb dimensions and dimmability as well as appearance.
E14 vs E27: what is the difference?
Both use screw connections, but their base diameters differ: approximately 14mm for E14 and 27mm for E27. E14 commonly suits compact decorative fittings; E27 is used in many larger household fittings. They are not directly interchangeable. Never force a bulb into a holder.
What is a GU10 bulb?
GU10 is a two-pin twist-lock base commonly used on mains-voltage spotlights and downlights. Its two short bottom pins have widened ends that lock into a compatible holder. Unlike E27 and E14, it does not screw in; unlike B22, its pins do not project from the sides.
How to identify GU10
- Two short pins underneath the lamp.
- Widened or mushroom-shaped pin ends.
- A GU10 marking on the lamp or packaging.
- A compatible push-and-twist holder.
Typical applications include recessed downlights, surface spotlights, track lights, accent lighting and outdoor fittings specifically designed for GU10 lamps. Outdoor suitability depends on the complete fitting and its requirements, not the base alone.
Choosing a GU10 replacement
Browse replacement bulbs and check for GU10 compatibility. Compare beam angle, lumens, colour temperature, dimensions and dimmability after confirming the base and operating voltage.
GU10 vs MR16: do not rely on the bulb shape
MR16 describes a reflector format, not one single electrical base. Many lamps described as MR16 use a GU5.3 base. Similar-looking reflector lamps can have different connections and supply requirements.
| Feature | Common GU10 lamp | Common GU5.3 MR16 lamp |
|---|---|---|
| Connection | Short twist-lock pins | Two thin straight pins |
| Fitting action | Push and twist | Straight pin connection |
| Typical supply arrangement | Mains voltage | Low-voltage supply with compatible equipment |
These are common arrangements, not a substitute for the lamp label. Confirm the exact operating voltage and any transformer or driver requirements. Do not replace GU5.3 with GU10, or vice versa, because the front of the lamp looks similar. Changes to fixed wiring or supply equipment need professional assessment.
The base does not determine brightness
Once the connection is correct, compare these separate specifications.
Lumens: how much light does it produce?
Lumens describe visible light output. Two LEDs with the same wattage can produce different lumen outputs. Use our lumens-versus-watts guide to compare brightness and power consumption.
Wattage: how much electrical power does it use?
Wattage describes power consumption. Stay within the fitting manufacturer’s permitted wattage and operating requirements. An LED-equivalent brightness claim does not change the lamp’s actual electrical rating.
Colour temperature: warm or cool light?
Colour temperature is measured in kelvin. Around 2700K–3000K gives a warm-white appearance; around 4000K is commonly described as neutral white; 6000K–6500K looks cooler or daylight-white. These describe colour appearance, not brightness. Choose for the room, task and your preference rather than the base type.
Dimming compatibility
Only use a lamp with a dimmer when it is specified as dimmable, and confirm compatibility with that dimmer. A dimmable LED can still flicker, buzz or dim poorly on an unsuitable control. The base alone says nothing about dimmability.
Bulb dimensions and enclosed fittings
An E27 A60 and an E27 G125 can share a connection but have very different dimensions. Check overall height, globe diameter, shade opening, clearance and manufacturer requirements for ventilation or enclosed fittings.
Beam angle
For directional lamps such as GU10 spotlights, a narrower beam concentrates light over a smaller area, while a wider beam spreads it further. Choose according to the intended task and fitting, not wattage alone.
How to identify your bulb base before ordering
- Make access safe. Switch off and allow the lamp to cool. Do not work on energised equipment. If safe isolation, access or the fitting condition is uncertain, ask a qualified electrician.
- Read the existing markings. Check the lamp, original packaging and accessible fitting label for the base code and operating specifications.
- Check the connection. Compare the screw thread, bayonet pins or twist-lock pins. Never force a lamp that does not move normally.
- Record the specifications. Note base, voltage, lumens, wattage, colour temperature and dimmability.
- Check dimensions and application. Confirm the bulb fits and is suitable for enclosed, outdoor or specialist use where applicable.
- Ask before ordering if uncertain. Have clear photographs of the old bulb, base and printed markings ready. Do not dismantle a fitting or expose wiring to obtain a photo.
Can you change a fitting from B22 to E27?
Replacing a lamp holder is different from replacing a bulb. It involves electrical connections and may change the fitting’s suitability. Do not modify a fixed fitting simply because a preferred globe has a different base. Ask a qualified electrician to assess any proposed change. For a normal replacement purchase, matching the existing holder avoids unnecessary alterations.
Common bulb-base buying mistakes
- Ordering by shape: A60, candle and golf ball describe shape, not necessarily the base.
- Calling every screw bulb E27: E14 and other screw sizes also exist.
- Assuming B22 and E27 interchange: they require different holders.
- Confusing GU10 and GU5.3: similar reflector fronts do not establish electrical compatibility.
- Choosing watts instead of lumens: power consumption and light output are different measurements.
- Ignoring fitting limits: check dimensions, permitted wattage and operating conditions.
- Buying a decorative lamp for an appliance: ovens, heat lamps and other specialist applications may require purpose-designed lamps.
Frequently asked questions
Is E27 screw-in or clip-in?
E27 is a screw connection for a compatible E27 holder.
Is B22 screw-in?
No. B22 is a bayonet connection with side pins and a push-and-turn locking action.
Can I use an E14 bulb in an E27 holder?
Not directly. They have different base diameters and require matching holders. Do not force an incompatible bulb into place.
Is GU10 the same as MR16?
No. GU10 identifies a base; MR16 describes a reflector format. Check the actual base and voltage rather than the reflector shape alone.
Does the base tell me whether a bulb is warm white?
No. Read the kelvin rating for colour appearance and the lumen rating for light output.
Can every E27 or GU10 LED be dimmed?
No. The individual lamp must be specified as dimmable and compatible with the dimmer.
Can a bulb with the correct base still be unsuitable?
Yes. Voltage, dimensions, dimming, heat, enclosure and specialist application requirements can still make it unsuitable.
Final buying checklist
- Matching base and operating voltage.
- Suitable lumens and preferred colour temperature.
- Correct dimming specification and control compatibility.
- Appropriate shape, dimensions and beam angle.
- Compliance with the fitting’s wattage and operating limits.
- Suitability for enclosed fittings, outdoor use or specialist appliances where applicable.
Find the correct globe the first time
Compare bulbs and globes, or browse screw-in bulbs once you know the required base. Confirm all specifications on the selected product before ordering.
Not sure which replacement you need? Have a clear photo of the old bulb, its base and printed markings ready when asking the Whitehouse team for help. Include the fitting model, preferred colour and whether you use a dimmer. Do not expose wiring or dismantle a fitting to take a photograph.
Continue reading: LED vs Filament Bulbs: South African Globe Guide and Lumens vs Watts: How Bright Should an LED Globe Be?.
