E27 (ES) Bulbs

How to tell an E27 fitting

An E27 cap is a screw thread 27 millimetres across, which is where the name comes from. It screws clockwise into the lampholder and has no pins. The easy mistake is confusing it with E14, the small screw cap, which looks the same but is roughly half the width. If the old bulb has a large thread about the width of a thumb, it is E27; if the thread is closer to the width of a little finger, it is E14. A bayonet cap has two pins on the side instead of a thread and is a different fitting altogether.

ES, E27 and Edison Screw are one fitting

The same cap is sold under three names, which causes more confusion than it should. ES stands for Edison Screw, E27 is the metric designation, and packaging uses either or both. They are interchangeable: an ES bulb fits an E27 lampholder and an E27 bulb fits an ES one. The larger E40 cap, sometimes called GES, is used for high-bay and industrial lamps and is not the same fitting.

Shapes in this cap

E27 comes in more shapes than any other fitting. The classic GLS is the everyday pear-shaped bulb for a shade or an enclosed fitting, and spreads light in every direction. A globe is larger and rounder and is often chosen to be seen, in a pendant with no shade. Golf ball and candle bulbs are smaller and suit chandeliers and wall lights where a full-size bulb would crowd the fitting. Check the length against the lampshade as well as the cap: a bulb that pokes below the shade throws glare into the room.

Standard LED or filament

A standard LED has an opal or frosted glass that spreads the light evenly, and it is the better choice inside a shade or a closed fitting. A filament LED copies the look of an old clear bulb, with thin glowing strands inside, and it is the one to choose where the bulb is on show. Both are LEDs underneath and both draw a fraction of the power of the incandescent bulb they replace. In a clear glass pendant the filament version usually looks better; behind a fabric shade the difference is invisible.

Warm white, cool white or daylight

Colour temperature changes the feel of a room more than brightness does. Warm white is closest to the light of an old filament bulb and suits living rooms and bedrooms. Cool white is crisper and suits kitchens and hallways. Daylight is the bluest and is best kept for workspaces, garages and anywhere detail matters. Keep one colour temperature across a room: a warm bulb beside a cool one is the most common reason a new set of bulbs looks wrong.

Brightness, dimming and choosing the right bulb

Shop by lumens rather than watts, because an LED breaks the old link between the two. Match the lumens of the bulb you are replacing and the room will look the same, at a small part of the running cost. If the circuit has a dimmer, choose a bulb marked dimmable, since a non-dimmable LED on a dimmer will flicker or fail early, and older dimmers built for incandescent loads can misbehave even with dimmable LEDs. A modern trailing-edge dimmer is the reliable pairing. On an ordinary switch, a dimmable bulb works perfectly well and simply never uses the feature.

When the fitting and the bulb do not match

Sometimes the bulb you want is made in a different cap from the lamp you own: a decorative filament globe that only comes in E27 for a lamp that takes a bayonet, for example. A socket converter solves that by screwing or pushing into the existing lampholder and offering the other cap on top. It adds a little height, so check the bulb will still clear the shade, and respect the maximum load printed on the converter. For a permanent fixture it is usually better to choose a bulb in the fitting the lamp was built for. Converters earn their place for a single lamp you are fond of, or for a period fitting where the original cap is no longer made. Never use one to force a bulb into a fitting rated for less power than the bulb draws.