Choosing Halogen Bulbs

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Mains Voltage - GU10

The GU10 has two studs at the bottom of the bulb and a twist-lock action to insert and remove from the fitting. The reflector will generally measure 50mm across the face of the bulb, but other sizes are also made. It is a 240V mains halogen and is quite different from the 12V versions. The 10 in GU10 means there is a 10mm gap between the centres of the two studs.

Mains Voltage - G9

The G9 has two flat pins at the bottom and simply pushes into the fitting. The buld is a 'capsule' only and is very compact in size.

Low Voltage MR16 / GU5.3

The MR16 has 2 sharp pins on the bottom of the bulb and is simply a push fit into the fitting. This is a 12V lamp which requires a transformer and quite a bit larger than the MR11. It measures 50mm across the face of the bulb. The 5.3 in GU5.3 means that there is a distance of 5.3mm between the two pins.

Low Voltage MR11 / GU4

The MR11 has 2 sharp pins on the bottom of the bulb as well and is also a push fit into the fitting. It is a 12V lamp which requires a transformer, but what makes the difference between this and the MR16 is the width of the bulb. This measures 35mm across the face of the bulb. The 4 in GU4 means that there is a distance of 4mm between the two pins.