All shapes and sizes are represented by 2 & 4-pin bulbs, though the majority of them are Compact Fluorescent Lamps (CFLs) in various forms. These include 2 and 4-pin single, double, and triple tube designs. A single-tube version of a 2 or 4-pin lamp is turned so that it actually resembles two tubes, and this is generically known as a ‘Biax’ bulb. A double tube is commonly called a ‘Double Biax’, and a triple becomes a ‘Triple Biax’. Because each tube is doubled and resembles two tubes, you may encounter some confusing nomenclature (e.g. a Double Biax is occasionally called a Quad Tube Lamp).
Note that different manufacturers label these bulbs differently, as follows: Biax (GE), Lynx (Sylvania), Dulux (Osram), PL (Philips).
Also under the 2 & 4 Pin Bulb heading are Double D lamps (also called 2D), which come in either classic CFL guise or, more recently, in LED form with significant energy savings possible. These lamps are designed specifically for their low profile. The LED 2D lamps are retrofitting alternatives to CFLs, generally offering an energy-saving advantage of over 50%, as well as twice the lifespan, greater resilience to shock and vibration, reliable cold weather performance, lack of mercury, and instant full-power without the warm-up time required by fluorescent lamps. Some of the LED models also incorporate microwave motion sensors, which trigger the light when movement is detected. This is made possible through the sensor’s ability to penetrate the diffuser of a light fitting (PIR sensors cannot do this).
In all of these lamps, a selection of light colour temperatures is possible, and many of them are dimmable. Fluorescent lifespans tend to be from 6,000 to 15,000 hours in these lamps, whilst LEDs can easily extend to 30,000 hours.
Biax, Dulux, Lynx, PL, or Cluster bulbs (Philips tend to call multi-Biax bulbs ‘Clusters’) are commonly used in recessed ceiling lights, wall lights, and table lamps. Double-D or 2D lamps are specifically designed for use in low profile surface and recessed fittings, and are often used in bulkheads.
GR10q (4-pin); GR8 (2-pin); GX24d-1; GX24d-2; GX24d-3; G23; 2G7