Some tail lights have nice slow strobe patterns. Headlights that flash always flash in an annoying way. Why don't they make headlight that had slow strobe patterns like some tail lights? Like gradually getting brighter, then dimmer....

I'd say it's for a few reasons. One: If the biker is using the strobe to see (bad idea, but it happens nonetheless.) the slower the strobe the longer the biker is riding without light.

Slower strobes also increase the time to be seen by other cars. Say the strobe was at a frequency of 1 Hz (a slow strobe.) If the driver looked in the direction of the biker the moment the light turned off, it'd be a full half of a second before they'd be aware of the biker, assuming the driver couldn't see the biker otherwise. A half second at 30 MPH for the car and 15 MPH for the bike means ~33 feet can be covered between the two of them before the light comes back on. That even applies for dimming lights. Below a certain luminosity the light can't really be seen anyway.

Also, dimming lights is expensive and complicated. (In terms of mass production where saving fractions of a penny off of a part makes a huge difference.)

The strobe function is SUPPOSED to be annoying. That's it's purpose... It's attention grabbing.

My Light & Motion Urban 800 has a "slow strobing pattern" that is really more a "pulse" than a strobe. I greatly prefer it to front lights that strobe. I assume all of the L&M Urban lights have the same feature.

The Lezyne KTV headlight has a slow strobe; perhaps their more powerful lamps do as well.

Also, the Knog Road 2 & 3 models have dual emitters and their flash mode alternates between the two at a nice, calm, slow rate.

Dinotte has one...I use it at night with a steady head light.

Most of my cheap headlights have a 2 or 3 hz strobe, which IMO is about ideal. One has a very fast, about 10 or 15 hz strobe, which is horrible and I never use it.

Agree 2-3 Hz is best for conspicuity without being annoying. A trike rider around here has a bright front light that's about 1/2 Hz. I see a flash in my peripheral vision, look toward it, and it doesn't flash again until I'm looking somewhere else.

Yep, my Lezyne Super Drive XL does about 1-2hz in flash mode. It's really bright and noticeable even in direct sunlight. I won't buy a front light if it only offers the annoying strobe effect flash mode.

In case you, like me, didn't understand the Hz references:

Wikipedia says:

I think the new Specialized Flux has a "strobe" pattern that's more of a "bright to dim to bright to dim" progression that never turns the light off completely as well.

In the olden days we used to say c/s or cps (cycles per second). I think it was sometime in the late 60s when it was decided by some august deliberative body to change cps to Hertz (Hz) to recognize Heinrich Hertz's contribution to physics and radio.

"The SI unit hertz (Hz) was established in his honor by the IEC in 1930 for frequency, an expression of the number of times that a repeated event occurs per second. It was adopted by the CGPM (Conférence générale des poids et mesures) in 1960, officially replacing the previous name, "cycles per second" (cps)."

I like the periodic pulses rather than a constant flash. I don't know how people tolerate flashing lights, but I guess you can get used to anything.

Like the so-called "SOS" mode of some flashlights.

I think strobes are dumb.

I really like them, when in traffic, during daylight hours............ Try downtown Aurora on a busy day..........

How about design a headlight that is constantly on, but with changing patterns, such as slow circling patterns with LEDs arranged in circle (too fast would make it like emergency light), or slight change of color (say white/ivory/yellow, or bright/less bright)?

My cygolite has a different strobe mode. In one setting the light remains on, but then it flickers without dimming down or off.

My Magicshine 808ce has a slow pulse feature that's high/low instead of high/off. I can't tell if it's more or less effective than the faster strobes, but it works.

What makes strobing effective is that the on/off cycle looks like motion to the eye. Slight changes of color don't achieve that. Medium/fast circling patterns might.