Happened to me twice -- user error or light malfunction, I can't say for sure. What I do know is that on my evening commute, the tail light wasn't working when I arrived home.

Is there a simple method to ascertain the status of the light, while riding?

[EDIT]

Thanks for comments/suggestions. I've moved the tail light (Lezyne Femto) from the rear of the rear rack to the seat post. Now I can see the red light partially reflected by the rear rack, without having to stop or contort myself too much.

If it's located on the seatpost or thereabouts i just hold my hand behind it and make sure the light is shining on my hand.

I can't tell without looking.


Two blinkies helps solve the problem of batteries running out mid-ride.

Sometimes falling off the bike helps to see the light

most of my rear lights, I can tell just by looking down. I had trouble with my rechargeable lights dying on my fatbike in really cold weather, so now that bike has a dyno system. It was the last holdout because it costs so much. I really hated realizing I didn't have a rear light.

Go outside at night, turn the light on, sit on the bike next to something to hold onto, and look down to see if something like maybe the cassette gets any red light on it. Or get in line with something and look back to see if something is reflecting the red light. A road sign works for me sometimes. Then try it while riding. A good mirror makes this easy.

Good reason to have a second rear light and also a rear reflector. Note that using a dyno as the power source only eliminates one source of failure (the battery) and adds some wiring as an additional one. Still a good idea to have some redundancy since there are quite a few ways in which lights can fail.

This is an important comment. especially in the winter. In the low 20f temps batteries have greatly reduced run times. Important if you're on a long ride. Always have a back up light, front and rear. A good reflector can be extremely bright when hit by car headlights. I always have both. I do centuries in the winter, if the road is dry and no conditions that might make ice.

it's a hassle to stop & check your rear lights for sure. I do it tho. stop lights are a good time to do it. I dislike stopping tho. I use two, so redundancy helps. this fall, on my nite rides, I've been using them on steady, not strobe. been curious about battery life but didn't want to remove & test them. decided to ride them until 1 fails, then replace the batts in both. finally happened last week to one of them, so I have to re-batt them both after Thanksgiving

I use my mirror and look for reflections of the light.

I use two or more rear lights to minimize the risk of running ninja. My helmet always has front and rear lights that can be switched easily and visibly from steady to flashing.

Even my short hop local errand bike has two rear read lights -- a Planet Bike Rack Blinky 5, and a wheel powered magneto blinker. Usually I also wear a helmet with front and rear lights. My immediate neighborhood is the most dangerous part of any ride so I want to be seen. For the first mile in any direction it's all transient apartment complexes. Hardly anyone lives in this neighborhood longer than a year, they have no investment in any sort of "community" so most drivers nearby are reckless and indifferent. But as soon as I get a mile away we're into older stable residential homes and drivers are much more courteous and considerate.

When in doubt, I pull over to check.

With the Cygolite Hotshot I can check my mirror and see the light reflected off objects behind me, or even off the pavement. Unless I'm running steady-dim, which I use only for nighttime group rides or on the MUP. As soon as I'm in regular traffic I pull over for a moment to change modes.

With the helmet light, I can see the light and mode reflected off my shoulder or hand in my helmet mirror or handlebar mirror. Since I run a Blackburn 2'Fer with red/white-steady/flashing, my main concern is not inadvertently running it in white mode on the back of the helmet. It has a single button to cycle through all modes and a couple of times I've inadvertently switched to white steady or flashing when I was wearing gloves while operating the light without looking.

My lower power steady/flashers aren't readily visible through the mirror so I either trust that they're on, use a backup light, or stop to check. That includes my old style rear LED/reflector lights and flashing LED saddle light.

1. USB tail lights: battery can't jiggle loose
2. USB tails lights: not as big of a deal to recharge between every single ride, I keep the bike next to an electrical outlet with a usb charger and charge the light without removing it from the bike
3. Dynamo Tail Lights: the most reliable solution but also the most expensive by far
4. 2 Tail Lights: If one fails the other stays lit

I put my rear light on the left handlebar.

This provides two advantages:

1. I can easily see that it's on.

2. Drivers think that's the center of my bike and give even more room while passing.

Possible solutions:

• get a much brighter light like the Cateye Rapid X3, which will reflect on the surface behind and beside you
• get a app controlled rear light like the See.Sense or Garmin Vario

TL-LD720-R | CATEYE
https://seesense.cc/products/see-sense-icon-rear-light
https://buy.garmin.com/en-GB/GB/p/518151
https://buy.garmin.com/en-GB/GB/p/50.../010-01419-00#

Create a fiber optic sensor running back to your rear light, and make it such that you have a display where it's convenient.



Me , I can tell before i start out, my hub dynamo lights come on as soon as the front wheel turns.

And can later go out for various reasons. I've found both battery and dynamo lights to be pretty dependable but can't say I've found one type to be consistently more dependable than the other.

after 30 years one of the battery spring terminals on my Vista Light broke, but by then I had a spare light.

My '92 Univega came with a Vista light on the rear rack. Still works, although it's getting finicky -- the on/off button probably needs a squirt of electronic cleaner. The blinker has never worked, although it may be an earlier model that doesn't blink, dunno.

Not the brightest taillight but well suited to nighttime group rides and the MUP, and the reflector helps.

I have a Magnic Light in the rear. It works off the eddy current created by the alum rim and the magnets inside the light itself, which then turn and create usable current. I have it mounted on an extension off my rack since the light needs to be along the rim. Since the rim would get in the way somewhat if mounted on the brakes, this puts it where it is completely visible. No wires, no batteries. While the claim is "free energy", nothing is free. While I would challenge anybody to say they could feel the difference, that energy is coming from somewhere. I like to think it is coming from otherwise wasted energy.

And how do I tell it is working? I just look for the reflection in a parked car beside me.

cool, me too. not sure if we crossed paths before. I think I did meet 1 other BF member who does this. how is yours mounted? this is how I do mine

Once upon the time there was a suggestion on the Bikecurrent list to run an optical fiber from the back to the handlebars. I used that for a while. Then I ran a second pair of wires in my dynamo based system, from the rear light, back to the handlebars where I powered a small LED. Now I have a circuit that monitors how much current goes into the rear light. If all is good the indicator LED is on. If the current is too small, i.e. open circuit situation, or too high, short circuit, it goes off. I ride a lot in the darkness, so knowing that all is good and not needing to look at various side reflections and getting distracted is important for me.

If it's dark I can look down and see the glow on my hub, wheel, seat stays, etc. in the daytime I can see the glowing reflection on my brake caliper. It's too dim to spot while moving but it's something I can periodically check while stopped.

if you have a mirror you could also check the rear light with it.

For those with weak lights mounted out back; hang a foot out and see the light on your foot.