Serfas Thunderbolt (UTL-6) Taillight gives you style and safety in one high-powered and affordable package.
Being seen on your bike at night never looked so good with Serfas' Thunderbolt (UTL-6) Taillight. This USB rechargeable gem comes with 35 lumens of firepower while giving riders' several different rear facing mounting options.
The 30 micro-LED strip will let your presence be known to cars and bikes alike. With 8 different color options, your bike will definitely find its match.
Charge up, light up and get riding safely with the Thunderbolt.
Very bright, I noticed cars slowing down to pass. On the first charge I got an hour on bright and another hour with bright blink. I didn't really read the time's it would last, so going forward, I'll likely set it to dim blink. Mounting is simple and it stayed where I put it despite several jarring bumps. Disconnected from the bike, the straps come completely off and would be very easy to lose if I walked away with it and wasn't paying attention to securing them. Charging time from completely dead took 2-3 hours.
A Martz (Hamburg Twp, MI, USA)
Very Nice light, I live in Seattle & it works really good, I am certainly impressed and so are others who see it. The package had no Instruction Pamphlet, but there was one Caution printed on the box. It states as follows >'CAUTION: Do not look at or shine this lamp directly into eyes.'< Well as usual I ignored the caution print & was seeing red lines for sometime. This maybe a little over kill for a tail light so when you see it in the flesh do take the precaution, I wish I had done so. Worth every penny, 5 Stars from me.
Razer (Seattle, WA, USA)
bob (hamburg ,, PA, USA)
Easy to take from one bike to a other.
Doug (Kansas city, MO, USA)
I love it, I am told I can be seen very well. The only thing is that I can't tell when the battery is low.
stefan k (culver city, CA, USA)
Great light. Bright, versatile, well designed. My only complaint would be the use of the mini USB rather than a more common micro USB. I would really like to be able to charge it with one of the many cell phone chargers I have lying around at any given time.
Jason (Kalamazoo, MI, USA)
Purchased both front and rear lights. These lights are amazingly bright. They are easy to mount anywhere on the bike. USB rechargable (2 to 3 hrs charging gives 9 hrs of light) and lightweight. Easily removed for recharging or theft prevention. Highly recommend these lights to everyone.
Ron (Chesapeake, VA, USA)
Very impressed with the brightness and viewable angles of the light.
The only downside, those straps. I didn't realize at first that the small round hole was to hold the straps (semi-)permanently to the light. I lost one right off the bat (fortunately was found and returned to me a couple of days later).
James Parsons (Portland, OR, USA)
Would love to give this 5 stars because it's the most intense light I've seen that is usb rechargeable. However, I had to return the first one to the dealer because it stopped working and I'm having the same problem with the second one, although I seem to have found an after the fact fix. The problem is that if I ride in the rain or if the street is wet from rain the light stops working. If I plug it in to recharge it starts working again. But that's only after I get home or to the office. So I have to have use an older taillight simultaneously in case the Thunderbolt stops working. Not that it's bad to have two taillights but it's disappointing that this one will not work consistently. Prior to this Serfas I had the TL-STN which I also liked a light, especially for the price, but it stopped working the first time I rode in the rain and I just had to toss it because it was not rechargeable. I see that it now has a "more water resistant Silicon casing" so maybe you will also find a way to make the Thunderbolt waterproof (my guess is water getting into the usb port). Hope you figure it out because otherwise it's a fantastic light.
Mark (Atlanta, GA, USA)
AWESOME LIGHT !!!! I ride to work early in the morning its dark. Riding through the hills people come around turns and actually see me its super bright. you would have to be blind to not see me from a good distance. i can actually see it lighting the ground on my sides while im riding. AWESOME!!!!! well worth the price..thanks "SERFAS" and thanks ernie @G's cyclery in whittier, ca
chris (whittier, CA, USA)
Disclaimer: I work at Bicycle Garage Indy, and these are -so- much better than any other rear 'blinky' that they are flying off the shelf.
Even the low-output setting is brighter than most other lights. The viewing angle is very close to 180 degrees-- whereas most lights have a focused beam, and are really dim when viewed from the side. Also, most seatposts and seatstays are not vertical, so this is even more important for a light that mounts w/ straps like this one. I love that the black one pretty much disappears on a black seatpost-- very stealthy.
I wish for three improvements:
1) Micro USB
2) USB port on the end, so it could be charged on the bike.
3) An extra strap included w/ the light, because I'm pretty sure I'll lose one...
The verdict: I even bought one for myself, and I'm jaded! Also, I think I'll be buying a front one when the Monon Trail (our local bike/hike/jog/stroll/dog/rollerblade/birding/ice-creaming hangout) gets crowded this spring. Nothing "parts the waters" like a decent front flasher!
Mark (Indianapolis, IN, USA)
Its a nice light, the battery life could be better, thats why 4 stars. On low solid I have only gotten about 3 hours of life off a fresh charge, definitely no where near the 7 hours they advertise. I like the mount options, I agree with others about improving and attaching the straps and changing the charging receptacle to one of the ends. For the money its a good buy.
Kevin (Murrieta, CA, USA)
WOW - Totally love this light. Easy to mount. I put this light on my seat stays. It holds in place (even over some less friendly pavement). This light is BRIGHT (with a capital B)! I wanted a rear light that is light and powerful. Magic! As a guy that rides to work and back, it's nice to know that I'm seen from at least a half a mile (probably more) with this light. The flash mode gets attention (in a good way). I've had other lights, but this is by far the most powerful and bright. I would strongly recommend. My safety is worth the price.
P.S. the usb charging option is sweet (no more batteries hurray).
MDubois (Sandy, UT, USA)
I can't really add anything more to what has already been stated. It's the best rear light ever!!!
S.C. (Where I Live, UT, USA)
This thing is awesome!!! I don't have to use batteries all the time and it charges while I'm on the computer. Very bright and visible. I like the options for settings. I was caught in a long rain storm and 0 issues
Jason Bailey (Holland, MI, USA)
I haven't owned too many rear taillights for my bicycles, but when I went into my LBS and asked what would be their best option for my safety and to compliment my new road bicycle, they clearly pointed towards the THUNDERBOLT. I am very satisfied with my purchase... Although the price was higher than expected, but I'm not going to argue with that too much since my safety is priceless. I know everyone reading this is more interested in the faults of this system, so here are a few: On the brightest flash setting, the battery goes out too fast. It lasts much longer in the low-power flash setting, and that mode is still plenty bright in catching everyone's attention from behind. Also, there isn't a very solid warning to let me know when the battery is running low. I realize that a warning light may flash from the mini side display, but I fail to see how that's helpful when I'm always looking forward when riding (maybe a nice and clear beeping would be a good idea?). At first I was worried about not charging this system after every usage because I didn't want the battery charge life to falter... But that's not a good idea... It's absolutely a must to charge after every reasonable use just to be on the safe side. As others have mentioned, the two plastic straps are prone to getting loose and lost, therefore I try to be extra careful in making sure I don't misplace them. It would be nice if Serfas could've provided an extra strap or two. Other than all this nitpicking, the THUNDERBOLT is well-suited to being strapped to a nice performing road bike. It's not bulky at all, and it has high-quality lighting which I am thoroughly impressed with. I definitely am looking forward to buying a second one in the future because of my long and consistent daily riding. Thank you, Serfas!
Nawaaz Ismail (Plano, TX, USA)
Waiting to see how it performs in the 7 month raining season with usb port. Same concerns as others about straps (now have small hole around one of the cleats) and battery life (I've ridden with high blinking, lasted about an hour. have been using at low-blinking and was dead at the end of 4 hour ride this morning.)
Recharging - recharging light fades in and out while charging, and stays solid when fully charged?
Jim Henry (Portland, OR, USA)
The brightness is AWESOME -- guaranteed to be seen. Mounts easily, however, it slips off if the jarring is hard enough or rains heavily. It sucks because I just lost mine that way :(. It would be nice to have a better re-design of the casing to include a secure, quick-release clip or extra anchoring.
Rheaah (Mesa, AZ, USA)
Light works great. I strongly agree with the other reviewers suggestions for improvements. An audible beep to signal that the battery is getting low is an extremely good idea. I've also found that this light can be easily attached to the back of a variety of helmet designs by simply using large size #64 RUBBER BANDS !!! Try it, it's awesome. I put this thing on the back of my helmet up nice and high then I put their 60 lumen rechargeable taillight on my seat post. Two taillights is definitely better than one. CAUTION: If you are thinking about running a flashing red taillight on the FRONT of your bike, think again. The COPS have a legal right to pull you over and ticket you if you do this on the street.
David B. (Newark, OH, USA)
Well Above Average.
Diego Alves (Porto Alegre, BRAZIL)
I sincerely feel safer as a result of this taillight. It is very, very bright. I like the fact it has multiple brightness levels as well as two different speeds for blinking. This is the first and only taillight I've ever purchased so I'm not sure how it compares to other products out there.
I purchased this along with two TSL-350 headlights and I can say this much: I am so happy thus far, barring catastrophic failures of the devices, Serfas has a life long customer in me.
Brandon S (Whitmore Lake, MI, USA)
I thought that I'd give this light 4 stars due to the battery life on high beam. However I should have fully read this when I bought the light!
I have noticed whilst cycling down pitch black country roads here in Warwickshire that the back of me is lit up red. You literally can't be missed. I'm currently using one of these with a fibre flare on the back stay. I want to buy another to cover the fork too.
Charging would be fine if you were using a computer at work, just keep the charger on you. Takes around 3 hours from dead.
Definitely worth the price.
Robin (Warwick, UK)
Personally I love this little gadget. I say little, in a Great way, for it installs so easily, is super small, really light, and nearly unbreakable; yet, puts out a tremendous amount of light. Do not be mislead by its size because it puts out all the light, with multiple settings, that one could ever hope for.
Steven Davis (La Jolla, CA, USA)
When I use the thunderbolt it looks like a motorcycle tale light. The thunderbolt stands out to the cars that are coming up behind you making you visible to traffic. The cars give you space and go by you slower this light is awesome!!
Cory Williams (Los Angeles , CA, USA)
Very bright, cars can see you perfect at night and in foggy days. Perfect to avoid cars pass you fast in days with no so many light.
Fabrizio Von Nacher (Irvine, CA, USA)
The Thunderbolt Taillight is the best taillight I've owned, With four different modes to choose from it makes it impossible for cars not to see you while riding at night.
Thomas Jondall (rancho santa margarita , CA, USA)
Slim, sleek, and stylish! The rubber mounts work great to keep the light secured to the seatpost. The included USB cable makes charging at your computer during the day a breeze. The light intensity is impressive for the compact design. Great job Serfas!
Matt (RSM, CA, USA)
Very bright and easy to install. what I like the most is that you can install it anywhere on the back of your bike and knowing that everybody can see you no matter the angle of viewing
Tom (Melbourne, AUS)
I love the brightness of this light!! Would recommend it even though I find the following problems. You really need to press the on/off button hard to get it on or off. If you work in a place that has secure computers you can't plug it into the usb for charging so an optional wall charger would be great!!! Also it needs a more visible charge indicator. Hard to see the one on it. That said, this thing is a blast of light and you can't be missed with it. So BUY it.
Daniel (Orangevale, CA, USA)
This is one bright ass light! Easy to mount with lots of battery life for most any type of riding.
Tim (Saskatoon, Saskatchewan, Canada)
Very bright and easy to recharge.
However, it recharges at the fairly slow rate of 2-2.5 watts. Lithium batteries should take a charge faster than that say 5-10watts.
Since it has a USB plug, could you also give it an app that would allow us to program our own light behavior. Like flash rate, dimming amount, fade in/out, flash pattern, behavior on restart (last used mode vs selected default), double click mode option. At least reprogram from the factory to start in low power flash mode.
As other have said, I'd also like to see the USB connection be on one of the ends so it can be powered while on bike. Use the main LED as a battery meter on start up activating each led individually.
Including an accelerometer to use it as a brake light would be very cool.
Eric (anchorage, AK, USA)
Great light. It doesn't need to be on a perfectly vertical angle to be seen. It puts out a huge amount of light in every direction (high or low beam). I'm impressed with the amount of run time. I commute daily and this lasts 3 days for me on a 15 mile route. (and for the complaints about straps, no worries, just keep track of them). Ride on!
Charles Van Kempen (San Diego, CA, USA)
Awesome! Ridiculously bright. I can see light reflecting off of all the surfaces in front of and behind me. Tail light is just as great. Battery life can be a little short but it's convenient to charge up the light with a USB (though Micro USB, common for smart phones now, rather than mini, common for digital cameras, would have been better.) I actually didn't mean to drop $90 on lights, but I am really glad I did, and wouldn't be surprised if they pay for themselves in cost of batteries, or replacing other cheapo options when they get wet.
Mikhail (Berkeley, CA, USA)
Brightness and mounting convenience are top notch. Several riders in our cycle club have purchased these and use them regularly. Almost too bright at night on the high setting. I reserve that for bright summer daytime rides and use the lower settings for night time rides.
Doug Gerard (New Hartford, CT, USA)
Just Excellent! I have a head and a tail light for over a year. They are very bright and very easy to set up and remove from the bike. I've noticed cars slowing down and giving me enough space when passing by. A good set of lights such as this one can prevent accidents and save your life. Safety first folks!
Alex (Vancouver, BC/Canada)
The best and brightest! I put 2 on my bike and i feel so much safer.
Brad (monroe, NC, USA)
Check out how our new Thunderbolts turn this parking lot into a light show!!!
MTBR checks out the Thunderbolt at Interbike 2012
What a driver would see at 55 MPH riding up on our Thunderbolt Taillight.
Turbo Bob talking Serfas lights.
Review of the Thunderbolt.
Slowtwitch stops by at Interbike.
Scouting Magazine features the Thunderbolt.
New York Times features the Thunderbolt.
Review of the Thunderbolt.
Thunderbolt wins "Best Commuter Light" and "Most Innovative Light" award.
Texas Cyclist reviews the Thunderbolt Taillight.
Manhattan Magazine mentions our USB rechargeable lights in their March Issue (Page 50).
Turbo Bob's Bicycle Blog on the Thunderbolt.
Bicycling Magazine (South Africa)
Bicycling Magazine (South Africa) takes a look at the Thunderbolt.
Thunderbolt makes the LA Times.
Review of the taillight.
Featured on Men's Journal.com.
Men's Health Singapore (January)
Thunderbolt features in Men's Health Singapore (January Issue).
Tim Keith of LateNightParents.com reviews the Thunderbolt.
Cyclocross Magazine's Holiday Gift Guide.
Checking out the Thunderbolt
All Seasons Cyclist reviews the Thunderbolt.
Bike Rumor reviews the Thunderbolt.
"14 Cycling-centric gifts for the Rider on your list."
Billings Gazette offers "Tips for Seasonal Gifts."
Road Bike Action (January Issue)
Road Bike Action takes a look at 7 new lights including the Thunderbolt for the winter in their latest January issue.
Active Junky stopped by our Interbike Booth, and liked what they saw out of our Thunderbolt Taillight.
Road Magazine features the Thunderbolt.» Road Magazine
Urban Velo goes in depth on the Thunderbolt.
Bicycle Times Magazine
Thunderbolts featured in Bicycle Times Magazine.» Bicycle Times Magazine
Coming in at #20 on "25 Back-To-School Essentials"
Coverage of our Thunderbolt Taillight in Road Bike Action.
Coverage of our Thunderbolt Taillight on Kinetic Shift.
Coverage of our Thunderbolt Taillight on Bike Rumor.