Rocking a tail light day or night is the new normal. I’ve done it for several years now and find myself feeling ultra-vulnerable on the odd instance I ride without one. The Specialized Flux tail light is bright and tailor-made to work on most seatposts — even the aero Venge.

Specialized Flux Expert Tail Light Features:

  • Maximum safety — even in bright sunlight
  • 110 lumen max output
  • 1km visibility in midday
  • Dedicated mounts for 27.2, 30.9 and Venge seatposts
  • Light sensor increases output by 50% automatically
  • Flip-out USB port to charge in under 90 min
  • Three operating modes: Steady, 25 Lumens Surge, 5-55 Lumens Flash, 55-110 Lumens
  • MSRP: $100
Specialized Flux Expert Tail Light Review

Bright tail light on a rainy ride home.

Blinky blink-blink says Flux

If you have yet to hop on the tail light train, there’s something you should know: get one that is truly visible in the day because that’s when it counts. There was a time several years ago when I was riding through the rolling farmlands of South Dakota. When I got to a rare intersection, a farmer stopped alongside and commented on how bright my Bontrager Flare R tail light was. He said he could see me from miles away. If I wasn’t sold on daytime running lights prior, that sealed the deal.

Specialized is not being left behind the light revolution with the metal-cased Flux Expert. Boasting a bright 110 lumens, Specialized states that it’s visible up to 1km away in bright sunlight. That kind of visibility is always welcomed and is accomplished using a unique reflector system.

How does the reflector system work, you ask? Well, have a look at your car’s headlights. If it’s a few years old, chances are it uses a halogen reflector beam design. While the Flux doesn’t use halogen bulbs, it uses a single LED bulb for longer battery life in an ultra-compact design.

Specialized Flux Expert Tail Light Review

Simply plug it in and the blinking light says it’s charging.

The metal casing looks sleek and has a premium feel. Instead of mounting straps, the Flux uses dedicated mounts for 27.2, 30.9 and Venge-specific seatposts. While these mounts will work with many bikes on the market, I couldn’t test it on my BMC Roadmachine 01 because it uses a D-shaped seatpost and had to work out a shim of electrical tape aboard the new Cannondale Synapse (which uses a 25.4mm seatpost). It did work straight-up with the Ridley Fenix SLX Disc, so one of three worked out-of-the-box.

Again, if you ride a Specialized Tarmac, Venge, or Roubaix, you’ll be able to use one of the included mounts straight from the box. And, to be honest, a few wraps of electrical tape was all it took to get it to fit on the Synapse.

Popping the unit out from the mount and charging it is simple, and you don’t even need a separate USB cable. The Flux plugs into any of the hundreds of AC charging blocks you have lying around. The flip-out USB tab does require a butter knife or something similar to flip outwards — good for preventing mid-ride extension, but bad for fingernails.

Specialized Flux Expert Tail Light Review

Locked-and-loaded aboard the new Cannondale Synapse.

How about brightness?

Side-by-side with the Bontrager Flare R, the brightness looks about the same, but the blinking pattern is not quite as obnoxious, to be honest (obnoxious is a good thing in this case). The focused beam of the Flux doesn’t have as wide of a viewing angle, but it is very bright and visible. Have a look at the two compared side-by-side below. The brightness of the Flux pretty much dominates — so much that you can’t really make out the Flare R’s blinking until I move the camera angle.

There are four modes: Solid, 25 lumen surge, 5-55 lumens flash and 55-110 lumens (daytime flash). The brightest mode gets selected automagically in bright sunlight.

The Good

  • Solid-feeling metal casing
  • Integrated USB makes or easy charging
  • Ultra-bright for daytime use
  • Rapid 90min to recharge
  • Secure mounting system

The Bad

  • Fixed mounts limit usage
  • Upward-mounted design can interfere with saddle bags
  • Blinking pattern could be more random and attention-getting

The Bottom Line: Specialized Flux Expert

Bright and sleek, the Flux Expert tail light looks the part of a premium light and has several unique features as well. It is on the expensive side, but if you’ve got a Venge, this is your best option.

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About Author

A native of the Pacific Northwest, Jason quickly developed a love for the outdoors and a thing for mountains. That infatuation continues as he founded this site in 1999 -- sharing his love of road biking, mountain biking, trail running and skiing. That passion is channeled into every article or gear review he writes. Utah's Wasatch Mountains are his playground.

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