Buying a light bulb is easy until the base does not fit the socket. In South Africa, B22 bayonet and E27 Edison screw fittings are common, but GU10, MR16, G4, G9 and E14 also turn up in downlights, decorative fittings and table lamps. The fitting is the mechanical connection; voltage, wattage and dimming compatibility still need their own checks.
Light bulb fittings at a glance
| Fitting | How it connects | Where you may see it | Check before buying |
|---|---|---|---|
| B22 | Push in and twist | Older ceiling lights and lamps | Bayonet pins and voltage |
| E27 | Screw in | Pendants, table lamps and ceiling fittings | 27 mm base, wattage and dimming |
| E14 | Smaller screw in | Compact decorative lamps | 14 mm base and available space |
| GU10 | Push in and twist | Mains-voltage spotlights and downlights | Pin spacing, beam and fitting depth |
| MR16 | Two-pin push fit | Low-voltage spotlights | 12V system and driver compatibility |
Start with the fitting on the old bulb
Switch the light off, allow the bulb to cool and remove it without forcing the base. Look for B22, E27, E14 or another code printed on the metal cap. If there is no clear marking, compare the shape and connection with the table above, then check the fixture's instructions. A photo of the old bulb beside a ruler is useful when you need to confirm a small cap.
Do not choose a bulb from the glass shape alone. Two bulbs can look similar while using different caps, and an adaptor can change the fit without solving voltage, clearance or heat issues. Once you know the cap, browse the LED bulbs collection by the fitting you need.
B22 bayonet cap: the push-and-twist fitting
B22 bulbs have two small side pins. You push the bulb into the holder and twist it until it locks. They remain common in older South African homes and in fittings designed around bayonet lamps. Never twist a bulb that does not seat correctly; inspect the holder for damage instead.
E27 Edison screw: the larger screw-in standard
E27 is a 27 mm screw cap used in many pendants, table lamps and decorative ceiling lights. It is a practical choice when you want a wide range of LED filament, frosted, dimmable or smart bulbs. A screw cap still needs a firm, straight fit. Stop if the threads bind or the holder moves.
For a warm decorative result, compare the finish and shape of the bulb with the shade, then check whether the fitting and bulb are both rated for dimming. A dimmable bulb does not make a non-dimmable circuit safe to dim.
Smaller screw fittings: E14, G4 and G9
E14 is the smaller Edison screw fitting, often used in compact decorative lamps. G4 and G9 are different small fittings, usually found in decorative or specialist luminaires. Their similar size can be misleading, so match the actual base and pins rather than relying on the bulb's overall shape.
Measure the available height and width inside the shade. A correct cap can still be unsuitable if the bulb touches the glass, blocks ventilation or sits too close to the fitting. For a small lamp, an E14 LED bulb can be a better fit than forcing an E27 adaptor into a tight space.
GU10 and MR16: do not confuse the two
GU10 spotlights use two short pins that lock into a mains-voltage holder. MR16 lamps use two thin pins and are commonly part of a 12V system. The bases are not interchangeable. If the old lamp is MR16, check the driver and the system voltage before changing to another lamp type. For bathroom or damp locations, the fitting, holder and installation zone all need to be suitable; the bulb cap alone does not provide the protection.
Voltage, wattage and dimming checks
Most household fixtures use mains voltage, but low-voltage spotlights may use a driver. Read the fitting label and the bulb packaging together. Stay within the holder's maximum wattage, even when an LED bulb uses less power than an older incandescent lamp. For dimming, confirm that the bulb, dimmer and driver are compatible as a set.
Which bulb fitting should you choose?
Use the existing fitting as the starting point, not the trend or the bulb shape. This comparison keeps the decision simple:
| If the old fitting has... | Start by looking for... | Do not forget... |
|---|---|---|
| Side pins and a twist action | B22 bayonet bulb | Pin condition and holder rating |
| A broad screw thread | E27 bulb | 27 mm cap and dimming status |
| A small screw thread | E14 bulb | Shade clearance |
| Two locking pins | GU10 spotlight | Mains voltage and beam angle |
| Two thin pins | MR16 lamp | 12V driver compatibility |
Common fitting mistakes
- Buying by the glass shape while ignoring the base code.
- Putting a 12V MR16 lamp into a mains-voltage GU10 fitting.
- Assuming every LED bulb can be dimmed.
- Exceeding the holder's wattage or enclosing a bulb that needs ventilation.
- Using an adaptor without checking clearance, heat and electrical compatibility.
Match the bulb to the room
Bedrooms and living rooms often suit warm white bulbs, while work areas may need a clearer light. Decorative fittings benefit from a bulb that looks right when switched off as well as when it is glowing. For large or less common bases, check the dimensions and product notes before adding the bulb to your basket.
Future Light's LED bulb range is the sensible first stop for standard caps. The E40 LED bulb is an example of why the base code matters: a large lamp base belongs to a different class from household E27 or E14 bulbs.
Frequently asked questions
What is the difference between B22 and E27 fittings?
B22 is a bayonet cap that pushes in and twists, while E27 is a 27 mm Edison screw cap.
Can I use an E27 bulb in a B22 fitting?
Not directly. An adaptor may be available, but check clearance, heat, voltage and the holder before using one. Matching the original fitting is usually the safer route.
Do LED bulbs fit in all light fittings?
No. The cap, voltage, wattage, dimensions and dimming requirements must all match the fitting.
How do I know which bulb fitting I need?
Read the marking on the old bulb or fitting, identify the base shape and compare the dimensions with the product listing. If it is unclear, ask for help before ordering.
Are smart bulbs available with E27 or B22 fittings?
Yes, smart bulbs are available in common caps such as E27 and B22. Confirm the fitting, voltage, app or hub requirements and whether the bulb is dimmable before buying.
What is the difference between GU10 and MR16?
GU10 uses locking pins for a mains-voltage spotlight fitting. MR16 uses two thin pins and is commonly used with a 12V driver. They are not interchangeable.
