This is my personal view as a cyclist/commuter who also drives and has professional experience as a transport/highways engineer.
A decent amount of white light on the front in a fairly wide beam (lets say 200-500 lumen) improves safety and makes the cyclist visible, especially e.g. to drivers pulling out of side roads at T- junctions. As a further example from my experience if I use just a 'normal' > 200 lumen light on a country road then over half motorists coming the other way don't don't dip their headlights, thus dazzling me - either they don't see me at all (very dangerous) or more likely it is seeing the bright light coming towards then that triggers the average driver to dip their headlights.
Going beyond this to very intense lights, either through focussed beams or 1000+ lumens then rider has to be careful where they direct that light, shining bright light onto drivers eyes either through the windscreen or via their rear view mirror is simply hazardous, it does nobody any favors and is no better behavior than motorist dazzling cyclists with full beam headlights.
I dislike all flashing lights, I think they are just distracting and annoying. 1 or 2 decent solid red LED lights, set to constant mode, on the back is enough to make the rider conspicuous IMHO. I understand people who think a blinky rear light helps them be seen, especially if it is not particularly powerful and is supplementing another constant rear light. However on a few occasions I've cycled behind bikes decked out with multiple very bright flashing LED's and I've found the experience frustrating, it also affected my vision to all the other hazards on the road that I need to pay attention to as a cyclist.
As for flashing white lights on the front, (or I've even seen flashing red lights on the front) I really don't see the point and I just find these annoying and distracting. As a cyclist it is important to be seen, decent constant lights front&rear and reflective clothing do this. IMHO blinking lights at the rear and especially at the front don't add any value and actually increase hazards rather than reduce them.
I agree.
This is the main reason I despise LED bike lights, they are overcompensating for lack of light quality (even high cri LEDs are pathetic at showing the difference between oil and water etc.) by making LEDs brighter. (Generator run infinite runtime) incandescent lights and hid lights are much better around the 200 lumen level than LEDs.
But etiquette for cycling lights on the road starts there, lumens. No matter where the light is pointed, lumens matter. Because of rain (reflection) and hills, even with all the light pointed on the road in front of you, more than 200 lumens maybe 300 is too bright. It appears six to ten times as bright as a car light when at the same lumen level because the source is tighter( generally a car with halogen will be 400 lumens each normal headlamp, so a 400 lumen flashlight will damage the eyes 6x as much.) So, using more than that has to be angled with optics not reflectors, and only when the time is right. Using flashing is much better than strobe. Slow flashing where the light never completely fades off is best, and not more than one flashing unless somehow synched, or if both are flashing at far apart frequencies.
As a cyclist with years of expert experience headlamps are silly to wear. Never seen it save someone's life. Maybe a flashing light as headlamp on 50 lumens or less but never as your source of light.
When stopped at a stoplight, turn off or cover flashing lights, but keep solids on. Don't track stop at night, and always keep headlight pointed straight and away from any mirrors.
In tunnels, turn only solid on, as well as single-lane roads that are two way, so as to prevent the flashing from throwing off driver's vision and let it adapt to your light.
Do not run flashing when in sidewalks, and in general, never ride on crosswalk-crossing sidewalks. Don't run flashing headlights on pedestrian trails either, mountain bikers should only run solid.
IMO best frequency is between 2ps and 5ps. Lower than two can work but over 5 per second is too fast. Rear light should always be flashing as to not be confused with normally-moving cars. Rear light power should be unlimited, still, more power than a Surfas Thunderbolt is too much for city commute, and again, try to cover it while stopped.
I've seen death and serious accidents. I know what cycling is in a medium sized city. Above is what I've learned to be polite and safe. Safety before politeness, it is safe to be polite though.
