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The Knog Plus Rear Light is an impressively simple light that weighs almost nothing, yet at 20 lumens is bright enough for a useful visibility boost. The magnetic mount, cable-free charging and decent battery life – given its tiny size – in the flashing modes make it perfect for winter training, though a limited burn time in steady mode can limit that option to commutes.
The key principle behind this is simplicity. The slim body is full of COB LEDs, and can be plugged directly into a USB port for charging, meaning no cable is required. Plus it's just 18 grams (including the mount), and the 'face' is only 66mm x 14mm.
The light attaches to its mount via a strong magnet, which loops via elastic band around your seatpost. Attachment is quick and easy, and the magnet means you can even reach back mid-ride and clip the light in. I really like how easy this is to pull out and charge directly from a USB socket.
The Plus can wobble more on aero seat posts than regular ones, giving the occasional rattle over sustained rough surfaces. You can clip it to a rear pocket, however, and it works well on the back of a helmet, too.
The Knog Plus takes four hours to fully recharge, and offers five modes. I favoured Pulse mode, which easily outlasts my winter rides with its claimed 8.5hrs. The longest claimed runtime is Eco Flash at 40hrs – it's still pretty visible, too – while the shortest is Steady at 2hrs.
I tested Steady mode at home and Pulse on my rides. Both matched the battery life claims, and a month's consistent use hasn't affected that. However, longer-term use can see that drop – while the light tested almost two years ago as part of the Knog Plus Twinpack is still in regular use, it now can't manage even 90 minutes on Steady.
That said, there's either variation between units, cold air really affects them or Knog has improved its batteries, as that original unit couldn't manage more than 1hr 45m while riding on Steady when new.
To be honest, personally I feel no need for a brighter rear light, as 20 lumens is easily enough for a driver to see me. Similarly, I have no need for a light to last longer than four hours.
Therefore, the Knog Plus meets my needs really well and is far less bulky than many brighter, more feature-rich and expensive lights.
The retail price for the Knog Plus is £17.99, and for that the value is excellent. The only cheaper one we've reviewed in the last two years is the BBB Spot Rear Light at £14.95, but that has a more awkward mount, only three modes and a build that feels cheap even at that price.
The Topeak Taillux 25, meanwhile, is £20, but bigger, heavier and not as bright as it should be.
I've been massively impressed with the Knog Plus rear light. It will appeal to both commuters and committed winter cyclists, and given its tiny size and weight (and affordable price) it's a great second light or emergency backup too. It's simple to use, easy to operate and a very handy thing to have.
Impressively simple rear light with good visibility and great design
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road.cc test report
Make and model: Knog Plus Rear Light
Size tested: 20 lumens
Tell us what the light is for, and who it's aimed at. What do the manufacturers say about it? How does that compare to your own feelings about it?
Knog says: "The Knog + (pronounced "plus") front bike light is a super-bright, 100% waterproof and totally versatile USB rechargeable bicycle light."
Tell us some more about the technical aspects of the light?
Dimensions: H: 66mm x W: 24mm x L:14mm
Weight: 18 grams
Charge Time: 4 hours
Modes (and lifetime)
Steady - 2h
Strobe - 8.5h
Pulse - 4.5h
Fancy Flash - 10h
Eco Flash - 40h
The Plus rear light pumps out an impressive 20 lumens of light and has 5 different light modes. It'll keep you lit up all night long, with run times of up to 40 hours on eco flash. Efficient Chip on Board (COB) LEDs designed to provide maximum brightness level for up to 90% of the battery burn time for each mode.
NO CHARGING CABLE REQUIRED
The integrated USB plug makes charging Plus is a breeze. No charging cable required, Plus plugs directly into USB ports & is designed to be exposed to the elements. Just remove from it's magnetic mount and you're ready to charge.
MULTIPLE MOUNTING METHODS
Where can you mount the Plus? Where can't you mount it! Handlebars, forks, seatposts, pannier racks and stays. Vertical and horizontal. Standard and oversize handlebars and seatposts (22.2 – 31.8mm+). Anything goes.
IT'S WEARABLE TOO
Swapping cycling for camping or running? No dramas. Remove the light from it's magnetic mount and it now doubles as a wearable night running light and versatile camping light. Use the clip to attach the light to your tshirt, shorts, socks, headband, backpack, dog collar (we could go on...)
Love how simple it is.
Charge time is four hours, and the run times match Knog's claims.
Steady - 2h
Strobe - 8.5h
Pulse - 4.5h
Fancy Flash - 10h
Eco Flash - 40h
The 20 lumens output doesn't sound much, but I found it highly visible.
No issues after a month of consistent use (and a previous test unit is still going strong after two years).
At 18 grams it's super light.
Compared to its competitors, a retail price of £17.99 is excellent
Tell us how the light performed overall when used for its designed purpose
Tell us what you particularly liked about the light
Slim, light and very easy to detach for recharging.
Tell us what you particularly disliked about the light
The mount could be more secure on aero seat posts... I got a few rattling noises over bumpy surfaces.
How does the price compare to that of similar products in the market, including ones recently tested on road.cc?
It's priced really well. The only cheaper one we've reviewed in the last two years is the BBB Spot Rear Light at £14.95, but that has a more awkward mount, only three modes and a build that feels cheap even at that price. The Topeak Taillux 25, meanwhile, is £20, but bigger, heavier and not as bright as it should be.
Did you enjoy using the light? Yes
Would you consider buying the light? Yes
Would you recommend the light to a friend? Yes
Use this box to explain your overall score
The Knog Plus light is exceptional. It does everything a commuter could want with ease, is tiny and weighs almost nothing, and is good enough for proper long winter rides too – in its longer-lived flashing modes, at least.
About the tester
I usually ride: S-Works Tarmac My best bike is:
I've been riding for: Under 5 years I ride: Most days I would class myself as: Expert
I regularly do the following types of riding: road racing, cyclo cross, club rides, Gravel on a CX bike