Sorry if this is a bit preachy, but I have ridden quite a few night rides these last few months and the standard of lighting adopted by fellow audaxers is somewhat mixed with some being appalling. I find this surprising, because as soon as the sun goes down then most audaxers put on all sorts of reflective gear, so it's clear they understand the issues, it's just clear that some don't understand how to maximise (or don't care about doing so) their lights to minimise the risks from other road users (including cyclists).
Front lights have their own problems, the mains one being getting a light that's bright enough to light the moon and yet doesn't dazzle oncoming traffic: just get a decent B&M dyno lamp, they have a cut-off at about 4º above the horizon, just like a car's dipped headlight (although without the "kick"), and are more than bright enough to ride solo in mid-Wales in absolute darkness at 50kph (they haven't discovered street lighting there yet*). Problem solved.
The aims of rear lights should be:
- Be seen by cars
- Don't blind other cyclists
- Be at least a bit legal
The big problems with rear lights appear to be:
- Crap lights
- Lights in a crap position
- Good lights on crap settings
So start with a good light: the best rear lights have a large surface area and aren't very bright: these give other road users the greatest chance to see you and to judge distance to you accurately. Cateye do some pretty decent rear lights like the Reflex, as do Busch & Müller: particularly the ones that include a reflector, which increases the surface area of the bit of red you're showing to road users behind and may even be road-legal**. Smart R1s are good lights as well, but you must use a reflector as well (they aren't road-legal on their own). Preferably have two lights for redundancy as well as emphasising you're a bike. Fibre Flares are rubbish as a rear light, because you don't look like a bike with them and as a car driver they are difficult to gauge distance to in the dark because the light is too soft; they're also not legal, so you still need a proper rear light; they
are friendly to other cyclists, though. Those pathetic little single-LED blinky lights embedded in a rubber assembly are rubbish verging on "just run me over, I deserve it"; most single-LED lamps are about as bad, even when set up correctly.
Set the lights up one above the other: as simonp pointed out, side-by-side and you look like a car in the distance, so drivers behind may overestimate your speed and come up behind rather sharpish; one-above-the-other and you look like a bike. The biggest mistake I have suffered from (on others' bikes) is that the lights are attached to the seat stays using compact brackets, which prevents the lights being pointed down far enough: the rear lights MUST point straight backwards, NOT upwards or downwards. If the bracket prevents you achieving a horizontal light beam then it's either the wrong light or the wrong bracket (for that part of the bike). If you have Smart R1s then you can get brackets designed for seat stays,
like these on eBay. If you have the 5-led Night Flares then these should NOT be mounted on the seat stays, because there isn't a bracket available to make them properly vertical in order to shine their light straight backwards (and they're not legal on their own either), although mounted to a rack they are very effective.
The point about rear lights is for other road users to see you, recognise what you are, and to cooperate on the road with you appropriately. Drivers are just like you and me and if flashing lights are annoying to cyclists, they are annoying to drivers too. The biggest problem with flashing lights is that when the light goes out, drivers behind can't see where you are; this is made even worse with flashing Smart R1s: the LED is soooo very bright that when the lamp is in the "on" state, it's blinding, and when it's in the "off" state then you can't see anything anyway, so really the worst of both worlds. Just set all your rear lights to steady and keep the laser-beam setting for high-risk situations, e.g. riding along dual carriageways, fog, heavy rain. If you have a legal reflector (you do have one, don't you?), car headlamps will light this up as well, adding to the overall effect of "cyclist". And nothing else quite screams "cyclist" in the dark as pedal reflectors, but that's a whole other topic ...
I have a
dyno-driven B&M Toplight Braketec just above the rear wheel (this is a German-legal light and reflector**); and because it's coupled to a B&M Luxos U on the front, which has an on-off switch on the handlebar, I can switch this rear light on while moving; the brake-light effect isn't very convincing, though. About 18" above that light
I have a Smart R1, which I don't usually use unless I am on my own, or the conditions require a "set-to-stun" light (fast and busy roads, poor visibility). And just above that
I have an old Cateye 5-LED LD500 set to steady (sometimes flashing in the day, but it's not very bright, just gets a bit of extra daylight attention). The overall effect is of two or three lights one above the other, none of them over-bright, none flashing, two are also reflectors, and enough light going backwards to alert other road users that I am there, that I am a cyclist, and for them to judge distance to me accurately in order to pass safely***.
The law is also quite clear: in the hours of darkness, you MUST have a red reflector on the rear and it must be visible only from the rear; you MUST have a suitable red light on the rear that must point backwards and be visible only from the rear. They can be one and the same unit. You don't need either during daytime.
As for group etiquette: if you set your lights up properly for road use on your own, the chances are you won't be causing any problems to other cyclists. If other cyclists are complaining then you really should look at your set-up, because firstly it's annoying other road users but more importantly it may be ineffective and even putting you in danger of getting knocked off. (When I rode London-Cambridge last year with my Smart R1 blinking away, I heard other cyclists saying "let's get in front of this bozo, his light's blinding me", and that was in the daytime! I switched it off after they'd passed and that was when I started thinking about effective lighting.)
As a footnote, I had an interesting conversation a few months ago in my LBS where I challenged them to sell me road-legal lights for use in the UK: they openly admitted that they couldn't. They could sell me lights that are legal reflectors (Cateyes), but not legal lights. All the lights that blinked also had a steady mode and so are required to satisfy British Standards. And they didn't stock German dyno lights off the shelf. Apparently nobody would buy the legal lights, because the standards are a bit out of date and so the lights are rubbish, they always buy the blinky LED ones instead. No bike shop I have been into since has stocked both a legal front and a legal rear light. Go figure.
And one more thing: don't forget to check your side-on lights/reflector profile, because cars pulling out of junctions (who are neither in front of or behind you) need to be able to see you as well.
* Not strictly true.
** Because of EU cross-border trading law, a lamp or reflector designed and built to an alternative European spec of an equivalent safety standard to British Standards is also legal for use in the UK. Only one reflector and light on the bike must be legal in the dark, the rest can be anything, so long as they don't dazzle or otherwise adversely affect other road users. Don't quote me on this, I read it somewhere.
*** Nothing's foolproof, though.
