PL Lamp Bases Explained: 2-Pin vs 4-Pin and G23, GX23, G24d, G24q

Plug-in compact fluorescent lamps — better known as PL lamps — power countless downlights, wall sconces, stairwell fixtures, and commercial troffers. Now that fluorescent lamps are being phased out, people are scrambling to find LED replacements. The single biggest source of confusion is the base: PL lamps use several similar-looking pin bases that are not interchangeable. This guide makes it simple.

First: Count the Pins

Every PL lamp plugs into its socket with pins rather than a screw thread. The first thing to check is how many pins it has:

  • 2-Pin lamps have a built-in starter and run on the fixture's magnetic ballast.
  • 4-Pin lamps have no internal starter and run on an electronic ballast — they're the type used in dimmable and programmed-start fixtures.

Pull the lamp out and look at the base. Two pins or four? That one observation eliminates half the catalog.

Then: Read the Base Code

PL bases carry a letter-number code stamped on the lamp or listed on the old packaging. The most common:

  • G23 — 2-pin, typically on 5W–13W twin-tube CFLs (small downlights, desk lamps).
  • GX23 — 2-pin, a slightly different keyed version, common on 13W twin-tube lamps.
  • G24d — 2-pin, used on 13W/18W/26W twin and quad-tube CFLs (magnetic ballast fixtures).
  • G24q — 4-pin, the electronic-ballast version of the same 13W/18W/26W lamps.
  • GX24q — 4-pin, used on higher-wattage triple-tube ("PL-T") lamps.

The letter "d" generally signals a 2-pin (two contacts) base, while "q" signals a 4-pin (quad-contact) base. The keying notch differs between them so the wrong lamp physically won't seat — a built-in safety feature.

Tube Shapes: Twin, Quad, and Triple

PL lamps also differ by how the tube is folded, which affects light output and fit:

  • Twin-tube (PL-S) — a single U of two parallel tubes; the most compact.
  • Quad-tube (PL-C) — four tubes folded together for more output in a short length.
  • Triple-tube (PL-T) — six tubes (three U-bends) for the highest output, common in commercial downlights.

Matching an LED PL Replacement

Modern LED PL lamps replace these CFLs while using far less energy and containing no mercury. To choose the right one:

  1. Match the base exactly (G23, GX23, G24d, G24q, GX24q). This is non-negotiable — it must seat in your socket.
  2. Match or exceed the lumens, not the wattage. A 9W LED PL typically produces 900–1,100 lumens, replacing an 18W–26W CFL.
  3. Pick your color temperature — warm 2700K–3000K for living spaces, cooler 4000K–5000K for offices, garages, and commercial areas.
  4. Choose Type A or Type B depending on whether you want to keep the existing ballast (Type A, plug-and-play) or bypass it (Type B, more efficient — covered in our Type A vs Type B guide).

Not Sure What You Have?

Bring the old lamp with you (or photograph the base and read any code printed on it). The base code plus the wattage is all you need. Browse our LED PL Lamps collection — every listing names the base, pin count, lumens, and color — and check the Bulb Bases & Filaments guide or our glossary for help. With fluorescent PL lamps disappearing, switching to LED now keeps your fixtures lit for years.

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