after about 26 years of riding without a light I finally bought one.

it has two settings...flashing/pulsing or solid.

what are the reasons why one better than the other or which situations call for either ?

Flashing can be more noticeable ... but very annoying when you ride in a group.

I use both. Flashing lights by themselves are hard to judge distance to, but are definitely the most visible at longer distances. In some parts of the world (NL for example) they may be illegal to use. My typical setup is a dyno hub driving a decent quality fixed tail light, then something like a Radbot or PB Superflash in blink mode on the seat post. I agree with Machka that they are annoying in a group situation.

I use a flashing during daylight hours, especially if it is overcast. It is amazing how far you can see a flashing taillight.

Aaron

Agree with above. Flashing for conspicuity. Steady to help others judge your position and speed. The steady light isn't really needed during the day, but helps a lot at night, IMO. Intensity is a major factor. In bright sunlight, you need a very bright blinky. Riding in and out of shadows during a sunny day, a bright blinky really helps drivers spot you when you happen to be in a shadow while their windshield is brightly illuminated by sun. At night, it might be too much and can dazzle drivers.

My .02¢ on the matter is that, aside from situations like Machka described where you don't want to annoy other riders, or perhaps pedestrians if you're on a bike path, you want to use the flashing mode primarily.

Looigi said the magic word: conspicuity. Typical city night riding is flush with light sources, and particularly steady ones, so a flashing light is more conspicuous in that setting. Rural night riding, where there are much fewer light sources and it's darker, either steady or flashing taillights are going to be easy to see (assuming decent and equal brightness in all of this).

I also agree with Looigi's assertion that a steady source is easier to judge location of (or distance to, in the case of a car driver approaching from behind), but I don't think that confers any additional safety in most circumstances. I don't have any facts to back that up, other than that I've never heard of that being the cause of collision ("I thought he was further away") and I've never experienced the phenomenon myself as a driver. So I won't argue the veracity of that claim, and I may be wrong, but given that we're probably talking about battery operated lights here, I'll just say weigh the potential of some gain in safety from a steady light against battery life and convenience; flashing mode will yield quite a bit longer battery life.

Compared to not using one at all, either mode is preferred, so just turn it on and hopefully enjoy many more years of safe riding.

I use a very strong rear light that I always set to "solid". It is really conspicious, even in the day (although I don't use it much in the day - mostly when I'm overly worried and have my daughter with me), but I think that being able to judge distances is one of the most important ones, as long as the light is strong enough to actually make you seen among the clutter of city lights.

My tail light is the Niterider Solas, and I am very happy with it. In fact, it is so strong, that I felt I had to point it ever so slightly downwards so as not to blind car drivers because their head is about the same height as the light is. It is also very visible from the sides, which I figure is at least as important as from the rear when riding in anything but the most rural areas.

My thoughts, flashing lights by day, solid at night.

I normally use blinking. Like the others said, it's more conspicuous; it's more likely to catch the attention of motorists. Also, it lends to longer battery life.

Yes. Some have touched on it already, but environment is a big factor. In a dark rural environment with no other vehicles, any light will stand out. In urban environments with many lights, illuminated advertising, and many vehicles' lights, a single steady light can just blend in. Flashing is good on emergency and law enforcement vehicles, school buses, road works, railroad crossings, airplanes, tall towers and buildings, life vests and rafts, etc...

My wired to dyno-hub head and taillight, are steady , because they are German made,

The accessory battery lights coming from Asian sources offer the flashing Option.

[Though Nightrider, I think is in San Diego, Cal]

How about one of each?

In many parts of Europe, flashing tail lights are not permitted.

Flashing mode usually extends battery life.

Red LEDs are already very low current draws ..

Yes. They want to reserve flashing lights for govt, law enforcement, road workers, emergency vehicles. As a cyclist, you're not entitled to a flashing light until after you've been hit and are in the ambulance.

Head light: steady for seeing, flashing for being seen. Use two after dark, and you have both bases covered.

Tail light: always flashing.

Front and Back Flashing if on the road. Both solid if on the bike trail. Especially in the winter (to see road, ice, etc. better...and be more noticeable) I'll also usually supplement with a dedicated headlight that is bright enough to see the road. I currently use a cygolite. I direct the cygolite towards to road (to see) and don't flash it (despite the setting)...it is painful in flash mode.

I always use a continuous light in the front. The rear light I leave on a blinking mode.

I'm among those that split the difference. During the day, I generally run with a flashing light on both the front and the rear. At night, I add a solid light to both ends. Only on relatively rare occasions will I set everything to flash, typically around dusk if there is an unusual amount of vehicular chaos present (commuting near the entrance of a large shopping mall on the run up to Christmas, etc.)

Flashing front and rear main lights in daylight hours. Both in steady mode in low light with 2 single LED lights of appropriate color at each end in addition to the main lights and lots of reflective tape on the bike and me. I just got a small LED light for my helmet as well.

+1

I have a flashing red light on the back of my helmet, and on the back of my rack.

I have a steady beam headlight on my handlebar and a white flashing LED on my handlebar.

I commute on a pretty busy road in the dark and have never had a problem.

Yep. It is used for some special conditions to attract attentions. Don't overuse it.

I have lots of reflectors facing aft - yellow on the pedals, one round red mounted on each seat stay, one round red on my seat bag, and one red on the back of the rack, and some white reflective tape on the rear rack stays. That is all in addition to the rear-facing yellow xenon strobe that is on day or night.

In the front I have a steady white LED light (used at night only), although I'm thinking of getting a new one that would allow for flashing mode as an attention getter for daytime road use.

I also always wear a reflective mesh safety vest, and reflective tape on my helmet that can be seen from all sides.

If a front light is bright enough, you shouldn't need a flashing light to get a driver's attention. And if the light isn't bright enough that you need to use the flash to get a driver's attention, you've wasted your money...especially in the day and age of $20 LED lamps that put out 600 or 700 lumens.

Rear lights are a different story. They aren't as intense (nor should they be) as front lights. Although the only thing I have to go on is personal observation, I run one rear light in steady mode so that drivers can judge the distance to me and several on flash to get their attention.

What you should need and what's best are two different things. Some motorcyclists have taken to running pulsing headlights to increase conspicuity and help prevent vehicles from pulling out or turning in front of them despite running high-beams during the day. It happens all the time; perfect visibility, you're there on your motorcycle plain as day with your highbeam blaring, and they still don't see you. Physically, the light travels through their eyes and forms an image on their retinas which send the info to the brain, but it doesn't register in their consciousness. Flashing/pulsing helps wake them up.