A floor lamp that stays exactly where you put it is doing quiet mechanical work every time you nudge the shade. Behind that small movement sit two very different spring families: compression springs, which push back when you squeeze them, and torsion springs, which twist and return. They usually live in different parts of the same lamp, they are rated in different units, and they fail in ways that look nothing alike. Knowing which one is under load — and what it is expected to hold — turns a drooping arm or a slipping height adjustment from a mystery into a repair you can actually plan.

Where each type shows up on a lamp

A quick way to tell them apart is to ask what the spring is resisting: a straight push, or a twist.

Compression springs

These work along their axis and push outward. On floor lamps you will find them in telescoping poles, where a spring-loaded pin clicks into a row of holes; behind push-buttons that release a height lock; inside friction collars that grip the inner tube; and in the contacts of the lampholder or the switch. They are the springs of linear adjustment and snap-fit locking.

Torsion springs

These work around their axis and resist rotation. They sit at elbow and knee joints on articulated arms, at the pivot that holds the shade angle, inside clamp levers, and in toggle switches. Wherever a part rotates and must hold a position against gravity, a torsion spring is a likely candidate.

One clarification worth making, because it saves confusion during a repair: the long springs running along the arms of a counterbalanced task lamp are usually extension springs, a third family that pulls rather than pushes or twists. The advice below about preload and fatigue applies to them too, but do not order a compression spring for that job.

Load capacity: force versus torque

You cannot compare these two springs with a single number, and that is the first practical trap.

A compression spring is described by its free length, its rate in newtons per millimetre, and its solid height — the length at which the coils stack and the spring stops moving. In a lamp height lock, the spring has to hold the weight of the upper pole plus the shade with enough margin that the pin does not creep out of its hole, but not so much that pressing the release button requires two hands. Too stiff is a real fault, not a virtue.

A torsion spring is described by torque at a given angle, with a rate in newton-millimetres per degree. Its job is to balance a moment, and moment is force multiplied by distance. A shade weighing about a kilogram sitting 40 cm out from a joint imposes roughly 4 newton-metres on that joint, before any linkage multiplies it. That is why a small spring at an elbow can hold a large shade — and why moving the pivot a few centimetres changes everything.

Both types also get stiffer as they deflect. Torque rises as the spring winds; force rises as it compresses. This is why a well-made lamp feels consistent through its range while a cheap one feels slack in the middle and stiff at the ends, or droops just past the point where you need it most.

Preload matters as much as rate. A torsion spring is usually installed with a couple of turns already wound in, so the joint is never loose at rest. A compression spring is often fitted partly compressed, so the pin sits under tension and does not rattle in its bore.

How they wear

Wear follows stress, and stress concentrates differently in each design.

In a torsion spring, the highest stress is on the inside of the coils and at the bent legs. Those legs crack first, often right at the bend, or the spring simply loses torque after years of cycling and the arm starts to sag. Grit between the coils accelerates the process, and a dry spring wears faster than one with a thin film of grease.

Compression springs are more often victims of their surroundings than of cycling. A spring left compressed for years can settle and lose a little free length, though in lamp duty this rarely matters unless it was already close to solid height. Thin springs in long bores can buckle. Damp rooms bring corrosion. But the most common height-lock failure is not a broken spring at all — it is a plunger seizing in its bore, or chalky dust and hardened grease inside a telescoping tube.

Before ordering any part, clean and re-grease the mechanism. A surprising number of "broken" height adjustments are just sticky.

Which one is easier to repair

Compression springs win this comparison comfortably, for one reason: they store far less energy in a form that can bite you.

A torsion spring under preload is a loaded tool. Release it carelessly and the legs snap round hard enough to draw blood or send a small part across the room. You also have to match details that are easy to overlook: wind direction (left-hand or right-hand), leg angle, and how many turns of preload the joint needs. Fit a spring wound the wrong way and the joint will fight you through its whole arc.

Compression springs are closer to drop-in parts. Match the dimensions, match or slightly exceed the rate, and the mechanism usually behaves. That said, an exact match still needs measuring rather than eyeballing.

Whatever you remove, record these five things before it leaves the lamp:

1. Free length and installed length, measured with calipers.
2. Wire diameter and outside diameter.
3. Number of active coils — count the gaps, not the end coils.
4. Wind direction and leg orientation, for torsion springs.
5. Preload setting, marked with tape on the joint before you loosen anything.

If a torsion joint is worn beyond a simple spring swap, replacing the whole joint assembly is often more reliable than sourcing a perfect match. Friction washers are a legitimate fallback for a shade pivot that will not hold its angle, though they feel different in use.

Matching the spring to the mechanism

The job decides the type, and substitutions across the two families rarely work. You cannot replace a torsion spring in a rotating joint with a compression spring, because the motion is in the wrong direction. Use the short guide below.

• Holding an angle against gravity: torsion spring with preload, or an extension spring in a counterbalanced arm.
• Locking a sliding pole at a height: compression spring behind a pin or button.
• Push-to-release controls: compression spring, sized for comfortable thumb pressure.
• Gripping a tube with adjustable friction: usually a collar or clutch rather than a spring at all.
• Consistent feel across a wide arc: torsion spring with a well-chosen rate, since the torque curve must match the changing moment.

Before you take it apart

Work with the lamp unplugged and the shade removed, so the mechanism is carrying less weight and less stored energy. Photograph the joint from two angles. Loosen torsion joints slowly and keep a thumb over the coils, and wear eye protection — the legs are the part that lets go. For compression assemblies, catch the pin and any small ball or collar in a tray; they are the parts that vanish.

When you reassemble, test the mechanism through its full range before refitting the shade. A joint that holds at the angle you need and still moves smoothly by hand is the sign of a spring matched to its job. If it binds, sags, or feels abruptly stiff, stop and check the preload and the alignment before tightening anything down. Ten minutes of patience here usually saves a second disassembly.

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