Lezyne Femto Duo

I like the Lezyne Femto Duo: it's a simple design with a range of blinky and constant settings that you fit to your helmet to use as a secondary light for both front and rear. It's mostly good news, but the Femto has historically had issues with waterproofing due to its combined lens/switch design and it continues to be an issue here. Unless you're planning to avoid wet weather riding you'll need to be vigilant to dry them out if they get wet.

Effectively this is just two single Femto lights with the backs removed, screwed onto a single helmet mount. Simple enough, and it works. You stick it on your lid by feeding a Velcro strap through the vents, so if you're using an aero/pisspot helmet you might be out of luck unless you stick the mount on with VHB tape or something similar. Anyway, if you have holes, it's easy. The width of the mount keeps it pretty stable but it does mean you can't fit it to the underside of your drop bar and use it as a running light there, which would be a useful second string to its bow.

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Using the lights is simplicity itself: hold down the lens to turn them on, click the lens to change modes, hold down to turn off. The two lights work independently so you can have any combination of the four flash modes and static beam. Lezyne claims a 60-hour runtime on two 2032 button cells, so if you're commuting half an hour a day you'll probably make it through the winter without having to replace them, and they're cheap as chips when you do.

You can't legally use this as your only light but it's more of an extra bit of visibility at a different height, to complement your main light. The fact that it's higher up means it's visible over stuff, and through stuff, that your main light might not be. So it's a helpful extra visibility aid after dark. And it's so light that you'll not even notice it on your helmet.

There's a thorn in the Femto Duo's side, though, and that's waterproofing. The lens has to move against the body to work as a button and water, it seems, can creep in there. After five minutes with me in the shower (and it's not even a very good shower) there was water in both front and rear compartments. Not much, but it will corrode the electrics and short the batteries if you leave it in there.

> Need more power? Check out our guide to the best front lights and our beam comparison engine

I dried my Femto Duo out on the radiator and it suffered no ill effects at all. If you're fastidious about doing that each time it gets wet then you'll probably have no issues, but really you want the Femto to be a fit-and-forget light, not one you have to remember and care for.

Verdict

Good extra visibility aid and easy to use, but waterproofing issues mark it down