Light Bulb Fitting Guide: E27, B22, GU10, G9 and More

2026 Update: Light bulb fittings are still one of the easiest things to get wrong when replacing a globe. The shape of the bulb matters, but the base matters more: screw, bayonet, pin, GU10, G9 and a few less common holders all fit differently.

Key takeaways

• Check the old globe base before buying. Do not rely only on the bulb shape.
• E27 is a large screw fitting, while B22 is the common bayonet fitting used in many South African homes.
• GU10, G4 and G9 fittings are common in downlights, cabinet lights, pendants and decorative fittings.
• Use the same voltage and fitting type unless a qualified electrician confirms a safe change.
• Adaptors can help in some cases, but they do not solve every size, heat, shade or compatibility issue.
• Once the fitting is correct, choose the right colour temperature: Warm White, Cool White or Daylight.

What is a light bulb fitting?

A light bulb fitting is the base that connects the globe to the light fitting and electrical contacts. It decides whether the bulb screws in, twists in, clips in or pushes into place.

Customers often say "bulb shape" when they really mean "bulb fitting". A round globe, candle bulb or vintage filament bulb can come with different base types, so shape alone is not enough. The safest habit is simple: check the code on the old bulb, or compare the base before ordering a replacement.

If you are replacing several globes in one room, check each fitting. Homes and guesthouses often have a mix of bayonet pendants, screw-base lamps and GU10 downlights.

Which light bulb fittings are most common in South Africa?

The most common household fittings are E27 screw, B22 bayonet, GU10 twist-lock, E14 small screw, G9 capsule and G4 low-voltage pin fittings.

E27 and B22 are the ones most people run into first. E27 is the larger Edison screw base used in many lamps, pendants and decorative fittings. B22 is the familiar bayonet cap, where the globe pushes in and turns to lock.

GU10 is common in mains-voltage downlights. G9 is often used in compact decorative fittings and some pendants. G4 and similar small pin globes are commonly used in low-voltage fittings, under-cabinet lights and older display lighting.

How do I know if I need E27, B22, GU10 or G9?

Look at the base of the old globe and match the connection style before choosing a replacement.

An E27 globe has a wide threaded screw base. A B22 globe has two side pins and locks with a push-and-twist movement. A GU10 globe has two thicker pins with widened ends, also fitted with a twist. A G9 globe has two small looped pins and usually pushes straight into the holder.

Do not force a globe into a holder. If it does not line up naturally, it is probably the wrong fitting or the old holder may be damaged.

In short: match the base first, then choose the bulb shape, brightness and colour temperature.

What is the difference between screw and bayonet bulbs?

Screw bulbs turn into a threaded holder, while bayonet bulbs push into the holder and twist to lock behind two small pins.

In South Africa, both are common. E27 is the larger screw fitting many people recognise from lamps and pendant lights. E14 is the smaller screw version, often seen in candle bulbs and compact decorative fittings. B22 is the standard bayonet size, while smaller bayonet fittings also exist in some lamps and older fittings.

If the old bulb says E27, replace it with E27. If it says B22, replace it with B22. If the label is gone, compare the base visually before buying.

When should you use a lamp holder adaptor?

A lamp holder adaptor can be useful when the fitting and globe base do not match, but the physical size, heat clearance and installation still need to make sense.

For example, an adaptor may let an E27 globe fit into a B22 holder, or change one common lamp-holder type to another. That can help when you have bought the right bulb style but the wrong base. It is not a fix for every problem. A large globe may still touch the shade, sit too low, block a diffuser or look wrong in the fitting.

Browse globe, bulb and lamp holder adaptors only after you know what base you have and what base you need. If the fitting is enclosed, old, cracked, heat-damaged or outdoors, rather ask before using an adaptor.

Which bulb fitting is used for downlights?

Many replaceable downlights use GU10 or MR16-style lamps, but newer LED downlights may have integrated LEDs with no replaceable globe.

GU10 lamps usually run directly from mains voltage and twist into place. MR16-style lamps often use two small pins and may be linked to a transformer or driver. Do not swap low-voltage and mains-voltage lamps casually; the fitting and supply must match.

If you are replacing a full downlight rather than just the globe, check ceiling cut-out size, driver requirements, dimming, colour temperature and whether the room needs a specific IP rating. For layout help, use our downlight spacing calculator.

In short: downlights are not all the same, so check the lamp base and the fitting type before buying.

What else should you check before buying a replacement bulb?

After the fitting is correct, check the bulb shape, size, colour temperature, dimming needs and whether the fitting is open, enclosed, indoor or exposed to moisture.

Some shades only accept narrow candle bulbs. Some outdoor fittings need a bulb that fits behind the diffuser without pressing against it. Some dimmers need compatible dimmable LED bulbs. If a fitting is marked for a maximum wattage, do not ignore it.

Colour temperature also matters. Future Light uses Warm White for 3000K, Cool White for 4000K and Daylight for 6000K. Warm White usually feels better in bedrooms, lounges and restaurants. Cool White is practical for kitchens, bathrooms and work areas. Daylight suits task-heavy spaces where a crisp look is wanted. For a deeper explanation, read our colour temperature guide.

Can you replace old incandescent bulbs with LED bulbs?

Yes, in many household fittings you can replace an old incandescent globe with an LED globe that has the same base, suitable shape and suitable electrical requirements.

The main mistake is buying by old wattage only. LED bulbs use far less power than incandescent bulbs, so compare the light output and the intended room use rather than assuming the same wattage number. Also check whether the old fitting is on a dimmer, because not every LED bulb is dimmable.

If you like the old warm look of a visible filament bulb, LED filament and vintage bulbs are usually the better place to browse than standard utility globes.

What should you do if the old bulb has no label?

If the label is missing, compare the base shape and measure carefully rather than guessing from the lamp or shade style.

Take a clear photo of the old bulb base and the holder. If possible, take the old globe with you when comparing options. For online orders, compare the product photos and fitting code. If you are still unsure, send Future Light a photo before buying.

This is especially useful for older chandeliers, imported lamps, bathroom fittings, cooker hoods, display cabinets and low-voltage downlights.

In short: a quick photo can save you from ordering the right-looking bulb with the wrong base.

Quick fitting guide

FAQs

What is the most common light bulb fitting in South Africa?

E27 screw and B22 bayonet fittings are both common in South African homes. The right one depends on the holder, so check the old bulb base before ordering.

Can I use an adaptor instead of buying the correct bulb?

Sometimes, but only when the adaptor fits safely and the bulb still has enough space. It is usually better to buy the correct fitting if you can.

Are E27 and B22 bulbs interchangeable?

No. E27 screws in and B22 uses a bayonet cap. They only become interchangeable if a suitable adaptor is used, and even then the physical fit must be checked.

Is GU10 the same as MR16?

No. GU10 and MR16-style lamps have different bases and may use different supply arrangements. Check the existing lamp and fitting before replacing a downlight bulb.

What colour temperature should I choose for replacement bulbs?

Choose Warm White for a softer home feel, Cool White for practical work areas, and Daylight for crisp task lighting where a bright appearance is wanted.

Should an electrician change a light bulb fitting?

Yes, if the holder itself must be replaced or the wiring needs work. Replacing a globe is simple, but changing the fitting is electrical work.