Caravan Light Bulb Types Explained

We often have a number of people enquire about the correct sizes and how to determine their light bulbs. There are a multitude of standards, bulb, and lighting types, which can become quite confusing.

Fortunately Caravans and RVs only use a limited few, and once you can identify the system employed, you only need to choose between fluorescent, incandescent, halogen and LED.

This guide covers the following common systems:
1) Edison Screw
2) Bayonet
3) Bi-Pin (includes G4 and MR's)
4) Festoon
5) Wedge

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1) Edison Screw

Developed by Thomas Edison, the creator of the electric light bulb, this standard continues to be used throughout the world today.

The most commonly used in households is the E27. E standing for Edison, and 27 relates to the size in millimetres across the thread. While these do exist in some RVs they are not as common as the other styles.

Above: The Edison Screw is not sold at Caravans Plus.

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2) Bayonet

This system is pretty much the standard for countries of the former British Empire such as Australia, with the most common sizes in Caravans and RVs being BA9, BA15s, BA15, BAY15 and BA22d. BA standing for Bayonet, the size in millimetres, and s for single contact or d denoting double contact.

12V Bayonet fittings with a single contact are identified by one contact plate on the base of the globe (see BA15s in image). This is the positive connection, whilst the outer metal shell offers an earth. The double contact has two contact plates. One being the positive while the other provides an earth.

In addition, BAY15 bulbs are also double contact. These 12V units are normally found in the tail lights of your Caravan, RV, or tow vehicle. The double contact points allow for dual function within a single globe. They are commonly used in tail and brake lights and can be identified by two filaments being present inside the globe. The side pins are offset on these so they can only be inserted one way.

BA22d is normally a 240V globe that fits most light fittings found in Australian residential dwellings. They are also used as the 240V function in many oyster style light fittings found in Caravans. While they are shown here with a filament, they are increasingly being replaced by fluorescent for cheaper running costs.

As with all bayonet fittings, the wattage can be found either printed on the base of the bulb or the glass itself.

Above: Bayonet fittings can be incandescent, LED, or fluorescent

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3) Bi-Pin

Bi-Pin or Bpin was first seen in 1893, and designed for Westinghouse as opposition to the Edison Screw. This standard is commonly used on globes such as halogen lamps and fluorescent tubes. The pins on some lamps (especially halogen) are placed closer together. This eliminates the possibility of using the incorrect type which could result in excess heat causing possible fire.

With the advent of LED, the Bi-Pin system is still used, however the heat generated is much lower than the output of halogen lamps. The use of the G4 standard with LEDs is simply to allow the LED version to fit into the existing receptacle.

The most commonly used standards in Caravans and RVs are G4, G5 and GX5.3 (there are others). The G prefix stands for glass, and the number, i.e. 4, means the pin centres are 4mm apart.

Apart from the multitude of smaller G4 based lamps, the MR or Multifaceted Reflector globes are probably the most common interior lighting system you will find in Caravans and RVs produced in the last 10 years.

Although there are three types, MR8, MR11 and MR16, the latter two are the most common you will encounter. The numbers represent the diameter. For example, the MR16 is 51.2mm. The 16 represents 16 x 1/8th of an inch. i.e. 3.2mm x 16 = 51.2mm.

Many Caravans and RVs may also make use of the G5 fluorescent tubes. These are usually around 16mm wide and 30mm in length.

In addition, there is also quad-pin base with two bi-pin pairs. These are used with compact fluorescent tubes that plug into a light fixture that has a permanent ballast such as the interior 12V caravan light pictured below.

Above: Samples of the globes that use the Bpin, additional forms are listed on our website.

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4) Festoons

Festoons, are an automotive standard bulb available in 6V / 60V configuration. In Caravans & RVs, these are mainly used in 12V clearance and marker lights applications.

They are measured by length, and width of glass. There are a number of sizes available ranging from 6.5mm to 15mm in width, and measure 24mm to 44mm in length. Wattage is normally printed on the metal cap ends.

Caravans Plus recommends using Bayonet or fixed LED for auto-lights due to vibrations effecting the reliability of festoon connections and filaments.

5) Wedge Bulbs

These low voltage bulbs have become common place within the automotive industry, and therefore have carried through to the Caravan and RV industry.

They work similar to the Bi-Pin system, however they have a sturdier base, and the wires run inside the globe itself. The body that holds the bulb in place is spring actioned, ensuring a positive grab. Wedges may also be double filament.

Wedges are commonly found in many Australian built caravans (including Jayco) who fit the Narva internal ceiling light systems.

By far the most common size is the T10. Always use a bulb of the same candle power to ensure the bulb does not burn back into its housing.