This is a topic that comes up a lot in online cycling forums and always seems to garner a rather polarized response - and I don’t get why. With the advent of new compact, high-wattage lighting systems cycling commuters have become either the haves or the have-nots. I’m a have-not by choice. I have a Light and Motion Vega light that only puts out 85 lumens. I can see fine with it on low power on the trail(1), reserve the high setting for rainy nights(2), and the flashing mode only when on city streets(3). The whole point of the light is for safety, and I outline my usage to maximize for each of these conditions below.
Trail use - this is where I hate the “me-first” Haves. They use their 700 lumen High Intensity Discharge (HID) light in conditions that do not warrant it. As the commuter density reduces, this is less of any issue, especially if the Haves use common courtesy and occlude their light with a hand over the bulb. My preferred usage here is to shield the left side of the light (right in UK/Aus) so that it doesn’t shine in the eyes of the oncoming rider. You still get to see with the rest of the light generated by your light, without blinding your commuting brethren. The worst offenders are the guys with helmet mounted lights that say hi to you as they pass and stare you in the face. Good luck people might as well ask me to ride while staring directly at the sun. Cover your light. Use a dim setting. Be considerate of others PLEASE.
Rain is tough. Seeing through fogged glasses, rainy conditions, and wet pavement can be a challenge. On those nights I skip the trail and go for a less-traveled road. You need the higher setting to pick your way through all the optical noise, but running a high setting can be brutal to the others who then have to add your bright beam to the mix of challenges.
City riding is the only use for a strobe flasher. It is intended to get the attention of drivers and is not to see by. You don’t need to get the attention of other cyclists on the trail, so turn off your damn flasher when on a trail. The only thing more blinding than a HID light is a flashing HID.
So please Haves - a little courtesy. It takes no effort to shield your light. There are plenty of Have-nots out there riding with 10 lumen lights with every right you have to the road/trail.
Oh - and for gods sake. Do NOT put a red blinker on your front. Red is for the rear, white for the front.