Solar string lights have a failure mode that nobody puts on the box. They don't usually die. They just get quietly dimmer, month by month, until one November evening you realise your whole garden is glowing like a dying phone screen.

Here's the part the marketing sheets skip: almost none of that dimming has anything to do with the LED. The diode is fine. The wire is fine. What's failing is the single hour of real sunlight the little panel on the end of the string never actually got.

The machine you're actually buying

A solar light is not a light. It's a four-part machine: a photovoltaic cell, a rechargeable battery, a light sensor, and an LED. The cell turns sun into electrons, pushes them into the battery, and a sensor flips the LED on when it gets dark. Break any one of the four and the whole thing runs dim or dead.

Now here's the trap. The three failures most of us can see — a cracked panel, a corroded clip, a browned wire — are the ones that are easy to spot. The one that actually ruins most installations is invisible: the battery is simply being undercharged because the panel never sits in the sun for the full window it needs.

The 6-hour rule

Manufacturers who tell you a solar string fully charges in a day are doing you a disservice. A sealed NiMH or NiCd cell (the 1.2V packs inside almost every unit) wants a solid 6 to 8 hours of direct, unfiltered sun to reach a full charge. Not "outside somewhere." Not "in the garden." Not "under the eaves where it looks bright enough." Direct sun, panel flat and facing the light, for the whole window.

Your balcony, your shade tree, your north-facing wall — those are all partial charge. And here's why partial charge compounds instead of just "lasting a bit less": a battery that only ever reaches 60% charge runs at a lower voltage the moment the sensor kicks it on, and the LED current drops. Your dimming isn't decay. It's a voltage floor you never climbed above.

The November effect

This is the part that catches people off guard. In summer, even a badly placed panel steals enough sun to stay bright. Then the sun drops, the angle steepens, the day shrinks from fourteen hours to nine, and the exact same panel — the exact same "good spot" — can no longer deliver those 6 hours. That's why a string that looked fine in July starts dying in November.

You didn't lose your lights. You lost the sun they were counting on. The unit hasn't aged. The geometry changed.

The battery is the weak link, and it leaks

Here's the bit that costs people more than it should. When a rechargeable cell dies — or when it's undercharged so badly it sits at a deep-discharge state month after month — it can begin to leak. A dried NiMH pack is a known source of the kind of acid that eats the contact spring and the little control board. By the time the light stops responding, the battery has usually already corroded the socket, and now a "cheap" fix is a new board.

Two practitioner rules. First, a dead or leaking cell comes out the same day you spot it, not "later." A defunct battery is a slow acid drip aimed at your electronics. Second, if you store any of these through winter, pull the battery. Leaving it in is how people wake up to a swollen cell and a ruined contact.

How to actually fix the dimming (in this order)

1. Clean the panel first, before anything else. A film of dust, pollen, or hard-water spots on a photovoltaic cell is a direct percentage of charge you lose every single day. A microfiber cloth and a wipe is the single cheapest brightness boost that exists. Do this before you spend a penny on hardware.

2. Move the panel, not the lights. The panel and the string can be on different parts of the garden. Put the panel where it gets the full 6–8 hours of direct sun and run the LEDs wherever they actually look good. This is the move that fixes more "broken" solar strings than any other, and it costs nothing.

3. Check the sensor is really seeing the sky. The light sensor decides when to switch on. If it's facing a lit doorway, a security light, or a bright window, it thinks it's still daylight and throttles or refuses to run. Point the sensor at open sky, not at another light.

4. Only then swap the battery. If the panel is clean, well placed, and the sensor is correct — and it's still dim by the middle of the night — the cell has genuinely lost capacity. Replace it with the same chemistry (1.2V NiMH/NiCd), and check the new one for a pull-tab that needs removing before it can make contact.

5. Look for the corrosion before it looks for you. A faint white or green residue on the contact spring is a battery that has already been leaking. Wipe it clean, dry it, and swap the cell. That residue is not a coating. That is the beginning of a short.

When solar is the wrong call

Being honest for a change: solar string lights are the wrong product for some jobs, and pretending otherwise is how people end up disappointed. If the string lives in permanent shade, on a north wall, or under a dense eave, no panel placement is going to save it and you should have bought a low-voltage plug-in run instead. If you want a reliable, every-evening glow, that's a different machine.

And where you do want guaranteed light in a spot that can't charge — a covered porch, an indoor table, a shaded nook — that's where a sealed flameless LED candle or a mains-powered set from our outdoor lights range is the honest answer. Don't force the sun into a shadow.

The test you can do tonight

Here's the clean way to tell what your string is actually doing. Give the panel a full day of direct sun, then cover it at dusk and time how long the LEDs hold brightness. If they're strong through midnight and gone by 2 a.m., you don't have a dead string — you have an undercharged one, and the fix is placement and a fresh cell, not a new box. If they're weak the moment the sun goes down even after a full day of sun, the battery has given up and it's time to replace it.

Solar lights aren't magic. They're a battery, a panel, and a clock. Treat them like that and they'll outlast the plug-in sets people brag about. Ignore the six hours and they'll dim to a whisper by November — not because they're cheap, but because they were never fully fed.