I think I have already made that clear in my posts above.

I wouldn't run only a single taillight because I've had them fall off or batteries go dead during rides. Personally, I use 3 taillights while commuting. One is on my helmet, one on my rear rack, and the other attached to the left seat stay. My rack light is non-flashing, and the other two pulsing.

Five or more taillights are more than I would want to deal with, particularly charging all of the batteries, but turning them all on and off would also be a hassle.

I like to alternate which light is on steady and which one pulsates, to try to equalize the battery life. Easy to do since both lights are the same.

Lol I like to specifically avoid equalizing battery life. Non-equal battery life means that if one runs out of juice, unlikely the other will as well. It would be hard to actually have them run out of battery at the same time, but the odds go up a little if you're switching between them.

So the simpliest way may be the best: pay no attention which light has more battery. Use them randomly.

I go with two this time of year, as well. Mainly for the reliability aspect: More than likely one will still be working when I get home.

Lol I prefer to use them the same all the time, that if one stops working I still have 50% life left in the other one to get home with, which will remind me to charge both. :-)

I have my single bright (Serfas 60 lumen) taillight cable-tied to my seat bag (see image). It isn't going anywhere (lesson learned the $ hard way). I take my bag off to recharge it In blinky mode it lasts a very long time so I have no problem with keeping it charged up. A co-worker said he saw it about 1/2 mile away in the daylight.

As a commercial truck driver in Portland and bike commuter, I completely agree with Patrick. Flashing blinkies are more difficult to place on the roadways. Much better then nothing, but slow pulsing or random flash with steady between flashes works best. Since switching years ago to a Hot Shot from Superflash and switching to a slow pulsing setting, I get much more room from passing vehicles.

It's also much better driving/riding behind none flashing lights.

Flashing lights cause me to look away from the light source, not what you want drivers to do.

Commercial truck driver in Seattle, and a bike commuter myself.

I like my combination of a steady dyno powered fender light, and a rack mounted multi function Cateye Reflex tail light. Th Cateye has a combination of a central focused beacon, and 4 wide beam emitters surrounding it.
My preferred setting, which is good for 120 hours, is a slow flash of the beacon, and the 4 surrounding emitters flashing in a random pattern best described as "glittering".

What about using two same taillights, both flashing in the same rhythm but opposite way: when one is on, the other off, and vice versa? Would it be closer to a solid one and help drivers tell the distance?

Splitting hairs, while adding complication?

Simply running a solid, and a flasher is the short way around the barn.

Based on previous posts up the thread, this evening I purchased a CygoLite HotShot 50 (https://www.cygolite.com/product/hotshot-50-usb/) from our local MEC store.

Wow, this is one bright taillight... 50 lumens, six modes including pulse, adjustable pulse and flashing rates, USB charging, all for $37.50 CDN.

Highly recommended!

Both flashing would save more battery than 1 solid and 1 flashing. Your solid one will go dim or off sooner.

The original HotShot was very directional, not much side visibility. How is this one?

Regular flashing modes are probably best for daylight riding. At night, I have two rear red blinkies. One flashes at a relatively low rate. The other is a PDW Dangerzone. It has two LEDS and there is a mode that has irregular flashing mode which makes it stand out from brake lights going on and off. You can see the flashing mode at 4:40 into this youtube video: https://www.youtube.com/watch?v=Nt72iJ2kWBI.

Amber lights.... no. You just look like the blinker on a car!

The other day I saw a cyclist with solid red leds on pant clips. The lights were pretty bright, and the two legs going up and down really got my attention. There wasn't a lot of traffic, but I found this a compelling add on.

This photo shows the tail light on the floor, shining up to the ceiling 101" away. The outer diameter of the ceiling circle is 40", the inner (brightest) diameter is about 16". Having said that, when looking at the light along a line just inside the outer diameter it is still very bright. So not much side visibility, but very effective across two or three lanes behind the bike (16'-20' wide at 100', 30'-40' wide 200') with a bright spillover width at least twice that.

Maybe yes, maybe no.
The Cateye Reflex flasher is good for 120 hours on the setting I use. My solid OE fender light is dyno powered, therefore has unlimited run time. I'm sure with a little research one could find flasher, and solid lights with similar run time if that's a concern.
While I have observed that a solid and flasher used together offer the "best" perceptive visibility, that in no way means two flashers are "bad", especially if using 2 flashers with dissimilar patterns.
It really is splitting hairs. The only really bad options are little or no lights, or lights that overwhelm those viewing them.

Very helpful perspectives from a cyclist and driver, thanks.

How's the actual run time per charge? The specs show up to 4-1/2 hours (presumably steady/bright) and 500 hours (not sure which mode).

I'm using a combination of a Blackburn 2'Fer on my helmet in flashing mode, and a no-name red LED in rapid flashing mode on the rear rack. In my videos it seems pretty much any combination of two rear lights helps give the viewer some sense of perspective and distance. As the distance increases/decreases the relative gap between the lights helps judge distance. Mostly I run both in flashing mode to extend battery life.

Regarding apparent brightness, I was a little concerned at first based on looking at the lights indoors. But outdoors in my video tests the lights didn't seem too bright, confusing or likely to cause a driver to avert his/her eyes - the LEDs are nowhere near as bright as typical emergency vehicle lights, street construction flashing lights or traffic lights. Perception seems to be relative to ambient light, iris dark-adaptation, etc.

There are a few tail lights that can put out an incredible amount of light which is fine in daylight, but very disruptive at night. Those that I've seen have a lower setting for night use, and the majority of users have the sense to use the appropriate setting.
One time I did need to stop after a cyclist passed me while using a ultra bright light as I couldn't see anything, and the flashing was giving me a mild case of vertigo.

Thats kinda the idea of using reflectors on the pedals. I've got reflective stripes in the crank arms as well. Not sure, though, how effective they are. But it is a cumulative effect, isn't it?

How does the higher seat height while in your truck affect your ability to see bicycle lights?

In general ones ability to see cyclists ahead of the cab is significantly better then average and easy to spot if using lights of any kind.

On the other hand, considering that semi trucks have 6 to 8 mirrors, cyclists using extremely bright, poorly aimed, or flashing headlights are a real and significant problem. it makes it virtually impossible to determine the location, and speed of a cyclist. It also conceals other cyclists and pedestrians from the drivers view.
Being 1 of 2 full time cyclists at a terminal of nearly 100 drivers, headlight overkill and helmet headlights are one of the biggest complaints I hear. When a coworker who just received his 25 year safe driver award, which means no tickets or incidents, on or off duty, says he finds them very disruptive, I take notice.

Ironically when showing a coworker, who is the other full time cyclist, my new Specialized Flux headlight, the first thing he said is "so you're going to be one of those guys with an obnoxious light?". Since he's on the driver safety board, I took the time to show him, and explain its not "one of those lights".

It would be next to impossible to keep both lights in proper sync. Even if they're just the tiniest bit out of sync, they will gradually go from flashing opposite each other, to flashing simultaneously, and back again. I've been in my car behind work trucks with flashing lights such as that, and it causes me to almost have target fixation as I watch the lights go between flashing directly opposite and in sync with one another. Extremely distracting.

While the beam appeared pretty narrow from a short distance (across a room), in practice from several hundred feet away it was still extremely visible. I want the new Pro 80, however, specifically because it has a diffuser lens in front of the LED. The 50 doesn't have that, but from the pic above it looks like it might be a little wider beam than the original.

Good observation. I make sure the hot spot circle of my headlight is entirely below the horizon, so to truck drivers it shouldn't appear any brighter than car headlights.

Would be interesting to know which is brighter:
Serfas 60 lumen or 80 lumen --versus-- HotShot Pro 80. I have the Serfas 60 shown in GeneO's picture in the above poast #58 , which is very bright. Anyone has both?