Home/Everyday/Light flickering

A failed filament stops. What flickers is a contact — and the contact is usually in the socket.

It flickers and then steadies · It flickers when the fridge starts · Only when dimmed, never at full · Several lights on the same circuit flicker together · The lamp has to be screwed in exactly right · It got worse over a few months · The socket looks brown inside · The bulb was changed and it still flickers · It stops if I tap the shade
FreeSwap the bulb to another socket — the flicker follows the fault
BoughtA new lamp, if the socket has gone brown
BoughtThe right dimmer for an LED load
Which part is flickering Why the socket goes first
Easy · 10 min · The test is one bulb moved from one socket to another, and nothing is opened

A pendant lamp: cord, conical shade, the socket below it and a bulb screwed in, with the filament visible inside the glass; below left, the socket in section — the threaded shell on both sides, the centre contact at the bottom, the side spring pressing on the shell and the terminals; right, three lamp bases side by side: a clean one, one with a pitted black centre contact, and one whose thread and shell are browned by heat

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what to touch fault correct Click the bulb, the socket or the lamp base

A contact fails slowly, and then fails faster

The spring that presses against the side of a lamp base is phosphor bronze, chosen because it holds its shape at temperature. But "at temperature" has a limit, and a lamp socket runs warm for hours at a time. Over years the bronze anneals — the internal stress that made it springy relaxes — and the contact pressure drops. Less pressure means a smaller contact area, which means higher resistance at the joint, which means more heat at exactly the point that is already hot.

That is a feedback loop, and it is why a flickering lamp gets worse over months rather than staying the same. The flicker itself is the joint making and breaking as the metal expands and contracts, and every break draws a tiny arc that pits the surface a little more. By the time you notice it, the socket is the part that has changed — the bulb is still perfectly good.

Which gives you a test that costs nothing and needs no tools: take the bulb out and screw it into a different lamp of the same type. If the flicker stays with the original lamp, the socket is at fault. If the flicker travels with the bulb to the new lamp, the bulb is. Nothing else in this job is as decisive, and it is the step people skip because changing the bulb feels more obvious than moving it.

The bulb's own contact, and the one that looks like a fault but is not

The centre contact of the bulb is a blob of solder, and repeated heating plus the pressure of the socket's centre contact flattens it into a shallow dish. A dished contact touches on its rim rather than its face, which is a small area and a poor joint. You can see it by looking at the base: a clean dome is fine, a flattened or blackened dish is not. If the flicker followed the bulb, this is why — and the honest repair is a new bulb rather than trying to build the solder back up.

And the case that is not a fault at all: an LED lamp on a dimmer. An LED draws a fraction of what the dimmer was designed for, so it may never reach the minimum load the dimmer needs to switch cleanly; and if the dimmer is an older leading-edge type it chops the supply in a way many LED drivers cannot smooth out. That flicker is worst at low settings and disappears at full — which is the signature, and no amount of screwing the bulb in tighter will change it.

Three rules, and the first is absolute. Switch off at the wall before you touch a bulb, and never open a socket or a fitting. Everything on this page is done with the switch off and the bulb in your hand; the terminals behind the socket are a different job with a different set of rules. If the socket is brown, brittle or smells hot, stop using the lamp. That discolouration is the plastic being cooked by a failing joint — a bulb screwed in tighter will not fix it and the next stage is a fire, not a flicker. Replace the lamp or the fitting. Do not "fix" a loose socket by bending the spring with a screwdriver while it is live. People do it, and it is the single most common way a flickering lamp becomes an injury.

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