Which Rear Bicycle Lights Should I use?

This is the companion article to Which Front Bicycle Lights Should I Use? Some of the background information and discussion of specific lights is covered in depth there and only peripherally referenced here. For best results start with that article and move on to this one afterwards.

… And Whats The Best Way To Use Them?

Just like in the companion article on front lights, I can’t tell you what the best lights are, or what the best lighting scheme is. What I can do is describe – as a daily commuter who has been refining his lighting setup slowly but surely for years – what I do and why. Use this as a guide to help pick out what you want your choices to be.

Executive Summary

Lets skip right to the good part. You can read the background info below if you feel like it.

• All light choices have been in use in all weather … except sub freezing sleet/snow. I live in California and while it gets down to freezing, thats about it. Rain but no snow.
• Use a pair of lights that display steadily. Either on the seatstays if you don’t have a rack, on your rack supports or best: out wide on your wideloaders.
• Where legal to use, add a blinking light (that does not blink steadily, but rather blinks in a varying pattern). Put it dead center in the back, between the two steady lights.
• Do not try and use lights that piggyback power off of your ebike battery or controller unless you have electrical skills and the desire to truly build something tailor made.
• Do use USB rechargeable lights. Invest in a powered (plugin) USB hub and set aside one day per week (assuming 2x daily commuting use) to charge up all your lights (I use this one).
• Pick lights that can be used as daytime running lights – use them on every ride day or night. So that means you want bright ones.

To Blink Or Not To Blink?

The reasoning and issues that cover blinking lights are covered completely in the companion post on front lights. Just refer to that. Here is a direct link to that section.

As described in that post, the best blinkers are the kind that use irregular, or ‘interruptive’ blinks.

Lights In Use or Worth Mentioning

I am using three different lights these days, and thought I would also mention the cheap ones that got me thru a few years of commuting safely, as well as another that turned out to be something of a dud.

The Knog Blinder Square (steady and blinkie)

This is now my favorite all-around go-to light for the back of the bike. It really shines (see what I did there?) as a steady light, but one of its many modes is as an irregular/interruptive blink that is very different from the Bontrager Flare RT described below. Is it better? Possibly not but if you find these lights on sale (as in: ebay) and you are willing to wait for delivery they are half the cost of the Bontrager light. Even at full price on Amazon they are significantly less expensive than the Trek/Bontrager light.

I made a short video showing the blink pattern below. My cell phone camera was unable to catch the fact that the inner and outer halves of the square are blinking alternately, so there is that added differential that is visible to the naked eye but not the camera.

The Bontrager Flare RT (blinkie)

This is probably the best-researched rear light on the market. Is it the best? Blinkwise, definitely maybe. Mounting-wise – definitely not. I certainly do like the one I have on my Surly Big Fat Dummy, but I had to get creative to get the thing mounted. The issue is its designed – pretty much exclusively – to be mounted on your seatpost under your butt. Thats great if you have no rear rack, or no saddle pouch under your seat for your tools and tube repair stuff.

Because I was mounting to the back of my Big Fat Dummy, I was able to fashion my own mount using a combination of a handlebar extension, a single Grin Technologies Handlebar Bob, a couple of zip ties and some gorilla tape.

Essentially, I used these parts to mimic an angled seatpost (the Flare RT mount is offset to point straight back behind the bike – assuming the seatpost is at its usual slant). If I had a normal bike rack I would have likely needed more tape (to build up the mounting surface for the Handlebar Bob to glom onto) and attached it to an existing rear horizontal surface of the bike rack.

In terms of the light it provides, it is strictly a blinkie, but it is one that is visible from a considerable distance without being particularly bright – In absence of brightness it provides a tightly focused beam that is visible from longer distances. I’m not sure if this is ideal in a busy urban environment, but it surely is in a rural setting.

One big negative of the Flare RT is it does not hold a charge during a period of inactivity. When taking the above pics, I tried switching my light on – to make a blink video like I did with the Blinder Square – and it was dead as a doornail. The light did recharge but the Knog lights sitting next to it – for just as long of a time unused – fired right up and worked fine.

The Knog Big Cobber (blinkie)

As noted in the article on front lights, I am using a couple of these on the front of a couple of bikes as front blinkers, and they might be overkill. The same is true in the back. I bought these before I found the irregular blink mode of the Blinder Squares, and before I had some time to evaluate the light. I am using it with its full 330-degree arc enabled, and in its short, sharp, intense ‘day flash’ mode. That may be ideal for daytime, but as winter commuting is here now I need to shift to one of its softer-transition blink modes for what is now a morning and evening commute in the dark.

At $125 for a pair of front and rear Big Cobbers, this is a very expensive light (the Amazon link above is – at time of publication – the best price you are going to find for a pair of them). This light is an excellent option, but its lack of an irregular blink – and the inability to add one in via the mode designer app – is a weird omission that makes the half-the-price Blinder Square or the Bontrager perhaps a better value.

These lights have many modes, and while I could use them as steady lights, I don’t. Two Big Cobbers in the back replacing the Blinder Squares on my cargo wideloaders – plus a third blinking in the middle – would be ideally visible… but at a cost that makes a trip to the emergency room a bit less expensive. If money is no object, these behemoths with their 330-degree light throw are as good as it gets.

RETIRED: The Night Provision LINE-120R

I used these on many bikes over a period of three or four years as both a side steady and a center blinkie. They are rated for 120 lumens, but those are Chinese marketing lumens and not standard ANSI lumens. These lights are bright, but they aren’t any 120 lumens.

At less than $13 each, they are cheap. They have enough battery capacity that they last an entire week of daily use (my standard for convenience is to charge once per week; charging all lights in my office garage via a USB hub). Lastly, having had them sitting on the back of one bike or the other for years in all weather commuting, grime and crud did not seem to faze them – even if the flimsy rubber cover over the USB charging port comes off (which it did on about half of them).

Bottom line: These are good, cheap, dependable lights. You get way more than you are paying for here (especially compared to the Blitzus I tried to upgrade into below). Of the 9 of these lights I own, only one went dead recently after three years of service. Not bad for $13.

The reason I spent the bucks and replaced them with Knog Blinder Squares is … the Knogs are bigger, brighter and more visible in broad daylight. This is where these lights fall down. They are visible in bright summer sunlight, but they more or less blend in with the bike rather than jumping out at you. The Knogs are similar… but they are a bit brighter, and more is better during the daytime. The added safety is worth that price to me. In addition to that they are notably larger and more visible at night and twilight.

BLAH: The Blitzu Cyborg 168T

I am listing this one as an example of what I considered to be a failure. Its a halfway decent light, but its not up to the task of daily use. I tried these out as an upgrade to the Night Provision lights. Just like the Night Provisions, I used them both for steady and blinkie lights.

On the plus side:

• At $16.95, its still cheap.
• It claims 168 lumens, which is more than the 120 of the Night Provisions. However once again these are Chinese marketing lumens and not ANSI lumens.
• It is physically larger for a further improvement in visibility over the Night Provisions.
• It uses exactly the same mount as the Night Provision lights, which gives me spares just in case.

On the minus side:

• Battery life at the more useful, brighter levels is poor
• Battery life from one light vs. another bought at the same time varies – some would last for half as long as another bought at the same time.
• I’ve had one die on me soon after putting it into service.
• The soft rubber battery cover can easily come off and result in a failure from water spray (a second failure in addition to the one that died for no reason).

In the end, these lights provided a minor improvement in visibility but battery life sucked and they were not reliable. For an occasional ride to the grocery store on a nice evening every once in a while they’d be fine. But nothing more.

Spreading Them Wide

Here’s something I have been doing that may or may not have any scientific basis. I asked myself what kind of light arrangement are drivers accustomed to seeing? Well … they see the taillights on other cars. And those consist, generally, of two steady lights, at the same height from the ground, spread widely apart. So I set out to try and replicate that layout as closely as possible.

In pre-dawn commutes I have come across recreational cyclist diehards out on their morning rides. Since I’m a fast ebike I’m able to approach and pass them fairly easily. In that overtake, where the two of us may be alone on a rural, dead-straight road with few or no street lights, I have personally experienced the issue that studies show blinkie lights suffer from when used alone: You know the bike is there because you can see the blink, but its really hard to figure out how far away it is or how fast its going until you get right up on it and light the rider up with your headlights.

For this reason, I want steady lights – in visual stereo to aid in motion tracking as much as possible. Admittedly that ‘stereo vision’ benefit is not a lot, but you do what you can.

I am of course also putting a blinkie in the center which is not something you see on a car. But that is a function of being a 2-wheeled bicycle sharing the road with 2-ton, 4-wheeled ICBMs crewed by inattentive pilots who – often as not – regard a bicycle as an annoyance unworthy of sharing the same road.

Is this the best way to do it?

Beats the hell out of me. With any luck – and I haven’t been hit from behind yet after almost 40 years of commuting in the saddle – I’ve given myself a fighting chance to keep the tire tracks off my back.