2D Lamps Explained: 2-Pin vs 4-Pin, Pictures, Wattages and Which One to Buy

2D lamps are still used across many UK homes and commercial buildings, especially in bulkhead fittings, communal corridors, stairwells, toilets, bathrooms, utility rooms and older low-profile ceiling lights. They give a broad, even spread of light from a compact square lamp, which is why electricians still get asked for them when maintaining older fittings.

The most common mistake is buying the right wattage but the wrong pin type. A 2-pin 2D lamp and a 4-pin 2D lamp can look similar from the front, but the base is different and they are not normally interchangeable. Before ordering, always check the wattage, colour temperature and whether the lamp has 2 pins or 4 pins.

You can buy 2D lamps from APM Plumbing & Electrical in Acton or order online using the product links below.

What is a 2D lamp?

A 2D lamp is a compact fluorescent lamp with the tube folded into a flat square or double-D shape. This design gives a lot of light from a shallow fitting, making it useful where a normal long fluorescent tube will not fit.

2D lamps are commonly used in:

• Communal hallway and stairwell bulkheads
• Bathroom and toilet ceiling lights
• Utility-room and store-room lights
• Outdoor bulkheads and porch fittings
• Commercial corridors, flats and landlord maintenance jobs

2-pin vs 4-pin 2D lamps: what is the difference?

The pin type tells you how the lamp connects to the fitting and control gear.

Important: do not force a lamp into the holder. If your old lamp is 2-pin, replace it with 2-pin. If your old lamp is 4-pin, replace it with 4-pin. The wattage and colour also need to match the fitting.

2-pin 2D lamps

2-pin 2D lamps are often found in older bulkhead fittings. The starter function is usually part of the lamp/base arrangement, and the fitting normally uses older-style control gear. If a customer brings in a failed lamp from a communal hallway or bathroom bulkhead and it has two pins, this is the section to check first.

Buy 2-pin 2D lamps

• Crompton CFL 2D 16W 2-Pin Warm White — useful for warm-white replacement jobs.
• CED 2D Lamp 16W 2-Pin 3500K White — good general replacement for many 16W 2-pin fittings.

4-pin 2D lamps

4-pin 2D lamps are common in fittings with electronic control gear and some emergency lighting applications. They are often marked as GR10q. The pins are arranged as a square group, so they are easy to spot once you remove the old lamp.

Buy 4-pin 2D lamps

• 2D Lamp 28W 4-Pin 4000K Cool White — GR10q — a strong replacement option for 28W 4-pin fittings.

Which wattage do I need: 16W, 28W or 38W?

The wattage should match the original lamp and the fitting. The most common sizes are:

• 16W 2D lamps — smaller bulkheads, bathrooms and compact fittings.
• 28W 2D lamps — larger bulkheads, corridors and communal areas.
• 38W 2D lamps — higher-output commercial fittings, where supported by the control gear.

If the old lamp says 16W, use a 16W replacement. If it says 28W, use 28W. Do not fit a higher wattage lamp just because it physically fits; the ballast and fitting must be rated for it.

What colour should I choose?

Colour temperature affects how the area looks:

• 2700K warm white — softer yellow-white light, often used in domestic areas.
• 3500K white — neutral white, common in corridors and general maintenance.
• 4000K cool white — cleaner white light, useful for commercial, utility and communal spaces.
• 6400K daylight — very cool/blue-white light, often used where a brighter daylight effect is wanted.

Can I replace a 2D fluorescent lamp with LED?

Sometimes, but not always directly. LED 2D replacement lamps can save energy, but the control gear must be compatible. Some LED replacements need the ballast bypassed, and some are designed for specific 2-pin or 4-pin fittings. If the fitting is in a communal area, emergency light, landlord property or commercial building, it is best checked by a competent electrician before changing the lamp technology.

For simple maintenance, the safest route is often to match the old lamp exactly: same wattage, same pin type, same colour temperature and same base.

Quick checklist before buying a 2D lamp

• Remove the old lamp safely and check the label.
• Count the pins: 2-pin or 4-pin.
• Check wattage: 16W, 28W or 38W.
• Check colour: 2700K, 3500K, 4000K or daylight.
• Check the fitting and ballast condition if lamps fail repeatedly.

Buy 2D lamps from APM Electricals Acton

APM stocks 2D lamps for electricians, landlords, maintenance teams and local customers in West London. If you are not sure which lamp you need, bring the old lamp into our trade counter at 24 Western Avenue, Acton, London W3 7TZ and we can help match the pin type and wattage.

Shop online:

• Crompton CFL 2D 16W 2-Pin Warm White
• CED 2D Lamp 16W 2-Pin 3500K White
• 2D Lamp 28W 4-Pin 4000K Cool White — GR10q
• Browse/search all 2D lamps on APM

APM Electricals — 24 Western Avenue, Acton, London W3 7TZ
Phone: 020 8702 8080 | Web: www.apmi.uk
Same-day collection available for West London trades.