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Which cap type do I need on my energy saving light bulb?

There are a wide range of cap types available for use in different situations. For ceiling lights, table lamps, chandeliers and other fittings which use "traditional" bulbs, the cap will most likely be a bayonet or screw thread cap, either BC, ES, SBC or SES.

For modern spotlights, downlighters and low voltage lighting, it is more likely the cap will be GU10, MR11, MR16 or G4/G9.

  • Diagram of a BC light bulb cap

    BC / B22

    These are the traditional bayonet caps commonly found on British light fittings. They are 22mm in diameter and should not be confused with SBC caps, which have a smaller diameter.
  • Diagram of a ES light bulb cap

    ES / E27

    Edison screw bulbs are screw threaded bulbs and are becoming more popular, especially on European-manufactured lamps. They are 27mm in diameter in contrast to SES threads, which are 17mm in diameter.
  • Diagram of a SBC light bulb cap

    SBC / B15

    These are the small versions of the bayonet BC cap. They are 15mm in diameter and commonly found on smaller bulbs in chandeliers and wall lights.
  • Diagram of a SES light bulb cap

    SES / E14

    These are the small versions of the ES cap. They are 14mm in diameter and commonly found on smaller bulbs in chandeliers and wall lights.
  • Diagram of a GU4 light bulb cap

    MR11

    This low-voltage halogen fitting comprises of two pins 11mm apart. Usually only found on halogen or LED halogen-type bulbs, the lamp is smaller overall than the larger MR16 fitting.
  • Diagram of a MR16 light bulb cap

    MR16

    This low-voltage halogen fitting comprises of two pins 16mm apart. Usually only found on halogen or LED halogen-type bulbs, the lamp is larger overall than the smaller MR11 fitting.
  • Diagram of a GU10 light bulb cap

    GU10

    This mains-voltage fitting comprises of two sturdy pins 10mm apart. Also known as Twist-and-Lock because of the way the bulb is inserted, the GU10 fitting is found on halogen, LED halogen-type and CFL reflector bulbs.
  • Diagram of a R7S light bulb cap

    R7

    This mains-voltage halogen fitting is found on outdoor floodlight bulbs.
  • Diagram of a G9 light bulb cap

    G9

    The G9 fitting is a halogen pin fitting, with the pins 9mm apart. The fitting is found on mains-voltage capsule lamps.
  • Diagram of a G4 light bulb cap

    G4

    The G4 fitting is another halogen pin fitting, with the pins 4mm apart. The fitting is found on low-voltage capsule lamps.
Need more help? See our guide to energy saving light bulbs