A solar light bulb is a self-contained LED light shaped like a traditional bulb: it charges from daylight and switches itself on at dusk, so it works with no electricity supply at all. It doesn't go into a lampholder like an ordinary bulb. Instead it carries its own solar cell, battery and light sensor, which is why people hang them in sheds, summerhouses, allotment huts, gazebos and tents – anywhere a cable run would be a nuisance or impossible.
The name covers both a fairy-light-style ornament and a genuinely useful work light, so it pays to know which one you're looking at.
All-in-one bulbs have the panel built into the cap, right above the hanging loop. They're light, cheap to run and purely decorative – a few LEDs giving a soft glow, often behind crackle glass or a fake filament. Hung in a cluster from a tree or pergola, they set a mood; on their own, they won't light a path.
Bulbs with a separate panel come with a small panel on a lead, usually a few metres long. You fix the panel to a sunny shed roof or fence and hang the bulb inside, out of the weather. These tend to have a bigger battery, a pull cord, switch or remote, sometimes a USB socket for topping up, and enough output – roughly 100–300 lm – to find tools on a bench or set a table in a gazebo.
You'll also come across bulbs on ground stakes for borders and pots, solar string lights made of bulb-shaped LEDs, and replacement solar tops that fit existing garden lanterns. Some separate-panel bulbs have what looks like an E27 screw cap; it's normally just there to fit the supplied hook holder. Don't screw one into a mains fitting unless the instructions say you can.
Ignore wattage claims such as "equivalent to 60 W" – on solar lights they're rarely meaningful. These are the figures that tell you how a bulb will actually behave in a British garden:
| Spec | Typical range | What it means in practice |
|---|---|---|
| Light output | 2–30 lm decorative; 100–300 lm with a separate panel | aim for 100 lm or more if you need to see what you're doing |
| Battery | NiMH 1.2 V (AA/AAA) or Li-ion 3.7 V | compare watt-hours, not just mAh: 1200 mAh at 3.7 V is about 4.4 Wh; 2000 mAh at 1.2 V only about 2.4 Wh |
| Run time | usually 6–10 hours after a sunny day | noticeably shorter from October to February |
| Colour of light | 2200–3000 K warm white; utility bulbs up to about 6500 K | warm white for patios and gazebos, cool white for sheds and camping |
| Weatherproofing | IP44–IP65 | IP44 under cover; IP65 if it hangs in open rain |
| Replaceable battery | yes or sealed | a swappable cell keeps the bulb going for years |
A shed or allotment hut is the classic case: running an armoured cable down the garden is costly and, for most people, a job for an electrician anyway. A remote-panel bulb gives you light at the flick of a switch for the few minutes you need it, and the battery stays topped up for the next visit. In a tent or campervan awning, a bulb with a hook and a switch does the same job as a lantern. Decorative bulbs, by contrast, belong where you sit in the evening – along a pergola beam, in a tree above the patio table, round the edge of a gazebo.
Most shells are plastic made to look like glass, which suits something that swings in the wind and may get knocked off its hook. Many decorative bulbs offer flicker or flame modes, and utility ones often have a dimmer setting that stretches the run time by several hours.
Face the panel south if you can, clear of overhanging branches, gutters and fence shadows. Behind a shed window it loses a good share of its charge, so mount it outside and run the lead in. Wipe it with a damp cloth every few weeks – pollen, dust and bird droppings build up faster than you'd think. If a security light or street lamp shines nearby, the dusk sensor may think it's still daytime and the bulb won't come on.
In winter, expect much less. Short days and a low sun mean a panel may only manage an hour or two of light. Before the first hard frost, charge the bulb, switch it off and keep it somewhere dry and frost-free until spring.
For a spot with no electricity, a solar bulb with a separate panel is the practical choice: it gives usable light and the panel can sit in the sun while the bulb stays dry. Where a mains supply exists, a weatherproof fitting with a standard LED bulb will always be brighter and more dependable.
Technically yes, but only a little. Indoor lighting delivers a tiny fraction of the energy of direct sun, so charging a solar bulb under a lamp is too slow to be useful. Models with a USB socket are the better answer on grey weeks.
For a shed, greenhouse or tent, one bulb with a remote panel usually is – it gives enough light to find tools or read a label. Decorative bulbs are a different matter: one on its own gives very little light, so they look best in groups of three or four.
Most are rated at least IP44, which copes with splashes and showers. For bulbs left hanging in open rain, look for IP65, and make sure the cap and battery compartment close firmly.
If the battery isn't sealed in, yes. Swap like for like – same chemistry and voltage – and never fit ordinary alkaline batteries. Cells usually wear out after a few hundred charge cycles, long before the LEDs do.
The LEDs themselves last for many years. The battery is usually the weak point and tends to need replacing after two or three seasons of regular use.
For conventional bulbs that run on the mains, from cap types to colour temperature, see light bulbs. If you'd rather charge from a USB lead than from the sun, read about rechargeable light bulbs.
