A flashlight for the car: what it must have

A car light has a different job from a hiking one. You do not use it every day, but you need it at the moment things get unpleasant: a flat tyre on the hard shoulder in the dark, a breakdown in an underground car park, hunting for something under a seat. That gives three requirements which have nothing to do with lumens – it must be charged, it must be within reach, and it must make you visible, not just the road.

When you are standing by a broken-down car at night beside a road, the biggest risk is not the dark. It is the car doing eighty that cannot see you. That is why a car light should have a hazard mode – a flashing or steady side light that marks you out from a distance.

The FL4 handles this with a side LED strip and a hazard light mode. The main reflector gives 310 lumens with a 150 m beam, which is enough to change a wheel or find your way on the shoulder; the side strip is there to show that someone is present. It also has a siren – sound works where light cannot reach, around a bend for instance.

One thing has to be said plainly. A flashlight's hazard mode does not replace the warning triangle or the high-visibility vest required by law. It is an addition that works on top of them, not instead of them.

The FL4 has a safety hammer for breaking a window and a seatbelt cutter in its tail cap. These are things you will never use – and if you do, it will be once and it will matter. Two practical consequences follow:

• It must be within reach from the driver's seat. In the boot under the spare wheel such a light is useless; it belongs in a door pocket or the glovebox.
• You must know where each function is without searching. Pick it up once when calm, find the hammer and the cutter, and try it dry.

Here is the biggest trap for a light kept in a car. A lithium-ion cell hates heat, and the cabin of a car parked in the sun reaches sixty degrees, the dashboard more. The cell will not be destroyed in a day, but it loses capacity far faster than in the shade. After two years on the dashboard, an FL4 will give you nowhere near what it would from the glovebox.

In winter the problem is reversed but milder. In frost the cell delivers less current and the light runs for less time. Warm it in your hand and the output returns.

The practical conclusion is simple. The glovebox or a door pocket, not the dashboard. And check and charge the light twice a year – the best moment is the seasonal tyre change, because you remember that anyway. We cover the behaviour of Li-ion cells in more detail in the article on Li-ion batteries in flashlights.

The FL4 has a solar panel on the body and it is worth knowing what it is for. It is trickle charging that offsets the cell's self-discharge – not a source that will fill the light from empty. Full charging runs over USB-C. So treat solar as insurance against the light being dead after a year in the car, not as a reason to stop charging it.

A second, ordinary light is worth having. The FL4 is a tool for an emergency; for everyday “let me see into the boot”, a small light you do not mind holding is better. The FL6 weighs 94 grams, gives 780 lumens and runs 18 hours at 120 lumens in Eco.

And if you drive long distances, the FL1 is worth considering. Besides 5,000 lumens and a 600 m beam it has a power-bank function and four 18650 cells totalling 8,800 mAh – you can light a whole accident scene and still charge a phone.

The FL1's power-bank function sounds like a guarantee that you will not be left without a phone – and that holds. What does not hold is what some people imagine: a light with a USB output is not a jump starter and will not start an engine. That takes a booster capable of hundreds of amps, which a Li-ion cell over USB-C will never deliver.

The siren gets overrated in the same way. It is a short-range signal to draw attention, not a device that summons help. And the hazard mode works at night; by day it shows little, and there the vest and triangle do the work.

With a car light, where you keep it matters as much as the specs, and there are three rules:

• Within reach from the driver's seat. The glovebox or a door pocket. The boot suits the second, ordinary light, not the one with the hammer.
• In the shade. The dashboard is the worst possible spot – it combines heat with sunlight, and the cell pays for it.
• Secured so it does not fly around the cabin under braking. A loose 255-gram light becomes an object that injures someone in a crash.

It fits into five points that take two minutes and are easiest to remember at the seasonal tyre change:

• Switch it on at full output and let it run for a minute.
• Test the hazard mode and the siren, not just the main light.
• Charge it fully over USB-C, even if the indicator claims it is nearly full.
• Check that the port flap closes and that the port is clean – the IP44 rating only holds with the flap shut.
• Put it back in its place, not in the boot “for now”.

In winter add one thing. If the car is parked outside, expect shorter runtime in frost. It is not a fault, it is chemistry – and after a few minutes in your hand or a warm cabin the output returns.

A checklist to finish. It lights, it is charged, it is within reach of the driver's seat, it has a hazard mode and it sits in the shade. Five points that will keep you from standing on a dark hard shoulder without light on a bad day.