Guide to Light Fittings, Caps and Bases

What Are the Different Types of Light Bulb Fittings, Caps and Bases?

When replacing a light bulb, choosing the correct light bulb fitting, cap, أو قاعدة is just as important as selecting the right brightness or colour temperature.

ال cap (also called the قاعدة) is the part of the bulb that connects to the light fitting. It provides the electrical connection while securely holding the bulb in place. Since different fixtures are designed for specific bulb types, manufacturers have developed a wide variety of light bulb bases to ensure only compatible lamps can be installed safely.

Whether you’re replacing a household bulb, a spotlight, or an LED tube, this guide explains the most common light bulb fittings, caps, and bases to help you find the right replacement.

Bayonet Cap

Bayonet caps are easy to recognize thanks to their push-and-twist locking mechanism. They remain popular in the UK, أستراليا, New Zealand, and several other countries because they are secure, موثوق, and simple to install.

BC B22 (Bayonet Cap)

القطر: 22مم

Pin-to-Pin Diameter: 27مم

Height: 26مم

ال BC B22, also known simply as ب22, is the standard bayonet cap used in many household light fixtures. It features two locating pins that lock into the socket with a short twist.

تشمل التطبيقات الشائعة:

• أضواء السقف
• مصابيح الطاولة
• Floor lamps
• Wall lights
• Decorative fixtures

Because of its durability and ease of installation, B22 remains one of the most widely used light bulb fittings.

SBC B15 (Small Bayonet Cap)

القطر: 15مم

Pin-to-Pin Diameter: 17مم

Height: 26مم

بصورة مماثلة, ال SBC B15 (Small Bayonet Cap) works in the same way as a B22 but is smaller in diameter.

It is commonly found in:

• الإضاءة الزخرفية
• شمعدانات الحائط
• إضاءة الأجهزة
• Small table lamps

Although most B15 bulbs operate on mains voltage, some specialist versions are designed for low-voltage applications.

Other Bayonet Variants

In addition to B22 and B15, several specialist bayonet fittings are available, مشتمل:

• B22d-3 – Often used in Fireglow and industrial mercury lamps
• BY22d – Commonly used for low-pressure sodium (SOX) إضاءة

Edison Screw Cap

Unlike bayonet fittings, اديسون المسمار (إس) caps screw directly into the socket. Named after Thomas Edison, they are now the most widely used light bulb bases worldwide.

ES E27

القطر: 27مم

Height: 26مم

ال E27 Edison Screw is the standard screw fitting throughout Europe, آسيا, أستراليا, and many other regions.

لكن, it is often confused with إي 26. Although the difference is only 1mm, the two bases are designed for different electrical systems.

• E27: 220-240 فولت
• إي 26: 110–120V (North America)

Always check both the fitting size and operating voltage before purchasing a replacement bulb.

SES E14 (Small Edison Screw)

القطر: 14مم

Height: 26مم

For smaller fixtures, ال E14 Small Edison Screw is the preferred choice.

You’ll typically find E14 bulbs in:

• الثريات
• Wall lights
• Decorative pendant lights
• إضاءة الأجهزة
• إضاءة مميزة

بفضل حجمها الصغير, E14 is especially popular for decorative LED filament bulbs.

Common Edison Screw Sizes

Capsule Lamps

Compared with standard bulbs, capsule lamps are much smaller and use two metal pins instead of a screw or bayonet fitting.

The model number simply refers to the distance between the two pins, making it easy to identify the correct bulb.

This design also prevents bulbs with different voltages from being installed in the wrong fixture.

G9 Base

تباعد الدبوس: 9مم

ال G9 fitting is designed specifically for 220–240V mains voltage.

You’ll commonly see G9 bulbs used in:

• Wall lights
• Decorative pendant lights
• الثريات
• Under-cabinet lighting

اليوم, LED G9 bulbs are widely available and provide an energy-efficient replacement for traditional halogen capsules.

G4 Base

تباعد الدبوس: 4مم

By comparison, ال G4 fitting operates on 12V and requires a compatible transformer or LED driver.

G4 bulbs are frequently used in:

• Cabinet lighting
• Display lighting
• Landscape lighting
• RV and marine lighting

GY6.35 Base

تباعد الدبوس: 6.35مم

ال GY6.35 capsule is another low-voltage fitting designed for 12V or 24V systems.

It is commonly installed in:

• إضاءة المهام
• Desk lamps
• Display cabinets
• إضاءة مميزة

لحسن الحظ, LED versions are available for all these capsule bases, making upgrades simple while significantly reducing energy consumption.

Linear Halogen

R7s Fitting

Cap Diameter: 7مم

Bulb Length: 78mm or 117mm

Unlike capsule lamps, R7s linear bulbs have contacts at both ends.

They are widely used in:

• Floodlights
• Security lights
• Work lights
• Uplighters

When replacing an R7s bulb, always match:

• طول
• القوة الكهربائية
• الجهد االكهربى

This ensures proper performance and safe operation.

Halogen and LED Spotlights

Spotlight bulbs are identified by the distance between their pins and the locking mechanism. بالتالي, different spotlight bases are not interchangeable.

GU10

يكتب: Twist & Lock

تباعد الدبوس: 10مم

Operating directly from 220–240V mains power, ال GU10 is the most common spotlight fitting used in residential and commercial lighting.

Nowadays, LED GU10 bulbs are available in various:

• Wattages
• Beam angles
• Colour temperatures
• Brightness levels

making them ideal replacements for halogen spotlights.

GU5.3 / السيد16

يكتب: Push Fit

تباعد الدبوس: 5.3مم

Unlike GU10 bulbs, السيد16 (GU5.3) spotlights require 12V power supplied by a transformer or LED driver.

They are commonly installed in:

• Kitchen lighting
• Display lighting
• Retail lighting
• إضاءة مميزة

GZ10

للوهلة الأولى, ال GZ10 looks almost identical to a GU10.

لكن, there is one important difference.

The GZ10 uses a dichroic reflector, which directs heat backwards rather than forwards. نتيجة ل, the base has a square profile that prevents it from being installed in fixtures not designed to handle the additional heat.

التوافق

• ✅ GU10 → fits GU10 and many GZ10 fittings
• ❌ GZ10 → should not be installed in GU10-only fixtures

Fluorescent Tubes and LED Tubes

Both fluorescent and LED tubes use two-pin caps at each end. لكن, different tube diameters require different base types.

G13 / T8

Tube Diameter: 25مم

تباعد الدبوس: 13مم

ال G13 fitting is the industry standard for T8 LED و أنابيب الفلورسنت.

After inserting the tube, simply rotate it to lock it into place.

The same fitting is also used on:

• T10 tubes
• T12 tubes

G5 / T5

Tube Diameter: 16مم

تباعد الدبوس: 5مم

في أثناء, G5 fittings are designed for slimmer T5 tubes.

These compact tubes are widely used in:

• مكاتب
• Retail displays
• Under-cabinet lighting
• Commercial lighting

The same cap is also found on some T4 fluorescent tubes.

الأفكار النهائية

ختاماً, identifying the correct light bulb fitting, cap, أو قاعدة is essential before purchasing a replacement bulb.

Whether your fixture uses a B22 bayonet, E27 Edison Screw, E14, G9, GU10, السيد16, R7s, أو G13 fitting, selecting the correct base ensures a safe installation and optimal performance.

أخيراً, if you’re replacing an older incandescent, halogen, or fluorescent lamp, consider upgrading to an LED equivalent with the same fitting. Not only will you enjoy lower energy consumption, but you’ll also benefit from a longer lifespan, reduced maintenance, and improved lighting efficiency.