The Topeak TailLux 40 DF is a bright and compact taillight designed to specifically work with Topeak’s Duo Fixer Mounting System. If you’re not familiar with the system, it’s a saddle rail mounting bracket that offers quick-release attachments for a variety of accessories. The TailLux 40 DF uses the upper slot of the Duo Fixer mount and offers a number of modern features. Topeak offers the TailLux 40 DF for $44.95 and includes a Duo Fixer bracket along with the taillight. It’s a 40 lumen taillight and offers three different output modes from constant to flashing. An integrated 160mAh Li-Ion battery provides up to 40 hour runtime when in the flashing mode. You don’t have to worry about charging cables as the TailLux 40 DF has a built-in USB-A connector that can be directly plugged into a USB port.

The Topeak TailLux 40 DF is a compact taillight that fits underneath your saddle using the Duo Fixer mounting system.

Retail Price$44.95
Measured Weight (in g)28 (taillight) / 32 (Duo Fixer bracket)
Likes+ Sleek mounting with Duo Fixer mounting system
+ Built-in USB connector eliminates need for charging cables
+ Curved lens improves side visibility
Dislikes– No mode memory means you have to cycle through all modes to turn light off
– Lacks a multi-level battery status indicator
Where to Buy (US)Todson


The Topeak TailLux 40 DF comes in a simple cardboard sleeve with specs and branding printed on it. Inside the box you’ll find:

  • TailLux 40 DF taillight
  • Duo Fixer mounting bracket

Interestingly, Topeak includes the Duo Fixer bracket with nearly every accessory which means you’ll probably have quite a few extra if you purchase multiple accessories. There is no taillight-only option currently available which could theoretically have a lower price.


One of the unique features of the Topeak TailLux 40 DF is the fact that it’s designed to work with Topeak’s Duo Fixer mounting system. It’s a clever dual-slot bracket that attaches to the rear of the saddle rails. The TailLux 40 DF slides into the top slot of the bracket and is secured in place with a spring loaded tab. Pushing down the release button on the bracket unlocks the taillight and allows it to be pulled out of the slot. The dual slot design of the Duo Fixer allows you to combine the TailLux 40 DF with a variety of accessories such as saddlebags (i.e. the Topeak SideKick) or fenders. The taillight tucks underneath the saddle for a sleek appearance. Note, the Duo Fixer mount requires 15mm of flat saddle rail and 38mm spacing between rails.

Topeak TailLux 40 DF Bike Taillight Review - Closeup
The Taillux 40 DF has a torpedo-like design that hides right underneath your saddle for a sleek look.


The Topeak TailLux 40 DF has a sleek torpedo-like shape that hides under your saddle. It’s a single LED design with a highly focused lens and curved lens to achieve a 240 degree visibility. The housing of the light is plastic with a matte black finish and the model name printed on the top. Branding is limited to Topeak on the rear of the taillight which isn’t even visible when mounted on the bike. There are two pieces to the taillight, the Duo Fixer attachment bracket and the taillight itself. Rotating the outer portion clockwise unlocks it from the base and reveals the built-in USB port which can be directly plugged into a USB Type-A port for charging. There are two markers on the base to visually identify if the taillight is unlocked or locked. The design is similar to the Light and Motion Vya and Topeak Headlux 100 and eliminates the need for a charging cable.

Topeak TailLux 40 DF Bike Taillight Review - Duo Fixer Setup
With the Duo Fixer mounting system you can mount the TailLux on the upper slot and accessories such as a saddlebag underneath it.

The user interface of the TailLux 40 DF is a simple one-level menu with one button interface. Rather than a separate button, the entire taillight lens acts as the button and can be depressed slightly downward. Topeak has utilized a simple short press design to cycle from off through the three output modes and back to off. This means there is no mode memory, you always have to cycle through all the modes to shut the light off. We would have preferred a more standard long press to shut the light off in any mode and mode memory to turn it back on in the last mode. Unlike the Magicshine Seemee taillights, there is no multi-level battery status indicator. Instead there is an easy to miss low-battery status indicator light on the body of the lens that illuminates when the battery is low.


Topeak has incorporated three output modes with the TailLux 40 DF: constant, flashing and pulse mode. Constant mode is 10 lumens with a claimed 3.5 hr runtime. Flashing mode is also 10 lumens but achieves the highest 40 hr runtime. Finally, pulse mode is a low-high style flash that achieves the full 40 lumen output with 20 hr runtime. Although there are no side cutouts on the taillight, the convex lens allows the taillight to be visible from side angles as well. The single LED design is quite focused which helps the TailLux 40 DF be visible at further distances. At only 40 lumens it would be a stretch to call the taillight day-time visible (i.e. compare it to the 450 lumen Moon Helix Sense) but it’s bright enough for nighttime riding or low visibility conditions.

Topeak TailLux 40 DF Bike Taillight Review - USB Connector
Topeak has integrated a USB connector directly into the taillight which means you don’t have to worry about charging cables.


Overall, we found the Topeak TailLux 40 DF to be a simple and well designed Duo Fixer compatible taillight. At 40 lumens the taillight itself lacks the power to be daytime bright and instead has a simple one-level menu and focused lens that’s well suited for nighttime riding or commuting. Aside from the clever built in USB connector, we’d score the taillight on its own an average score as the features and design don’t stand out in such a crowded marketplace. The main selling point for the TailLux 40 DF is the Duo Fixer compatibility which allows it to tuck underneath the saddle using the upper slot of the Duo Fixer bracket. It’s a clever mounting system that eliminates the need for fragile rubber straps or tools. The main negatives we found with the taillight is the fact that you can’t do a long press to turn off the taillight (e.g. you have to cycle through all modes to shut it off) and the lack of a multilevel battery status indicator. That said, if you’re looking for a solid taillight that’s compatible with the versatile Duo Fixer mounting system then the Topeak TailLux 40 DF is a good option.

Disclaimer: The product for this review was provided by Topeak. The views expressed on this website are solely those of the authors and are here to help people make an informed choice before a purchase. The authors or the blog itself does not get any monetary compensation from the product manufacturer or third-party websites/vendor links that are posted here.

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