TonyR wrote:Another aspect of the problem is the 3.5º problem. Because lights have to be taken on and off bikes to avoid theft (dynamo lights excepted), even if you were careful, setting the lights when you put them back its unlikely you would be able to set them up to the necessary accuracy. And you just need to look at the number of people cycling around with their rear lights pointed at the ground, sky or sideways to realise the 3.5º measure is meaningless to most people.
Cyclists have a lot less trouble aiming their headlamps than rearlamps. It comes naturally. We've all done it, riding along, into the dark, oh whoops, my light isn't shining on the road (or too close to be useful), reach for the lamp, give it a twist, all good now.
And in any situation where the ambient light level is good enough that you can't easily see where your headlamp is pointed and don't need it enough to bother improving its aim, you won't be dazzling anyone anyway, because glare only happens against a much darker background.
People who've studied this, find that cyclists generally aim their front lights so the brightest bit of the beam hits the road 10m to 20m in front and have them mounted between ¾ and 1m above the road. In this very non-exact science of simply getting into the right ball-park, the assumption is made that bike headlamps are aimed down at 3.5º. (That's 12m throw for a lamp 0.75m above the road, 16m if it's 1m up, so you see, we're in the right ball-park.) The eyes of anyone who's in a position to be dazzled will be higher than the lamp, so regulations put a top limit on the intensity of light emitted in the zone 3.5º and higher above the beam centre.
That does not mean you have to mount your light at exactly 3.5º, or that the whole exercise is rendered completely pointless if you aim it higher. I aim my light a bit higher than that, because I like to see at least 20m down the road. But most observers' eyes are somewhat higher than where my lamp is mounted, so the angle subtended at the lamp may nevertheless be at least 3.5º. And if it isn't, that's not the end of the world, for if my lamp is non-dazzling at 3.5º it doesn't suddenly become a monster at 3.0º.
Glare is not an absolute phenomenon but a highly subjective matter that comes on gradually with increasing contrast between a light-source and the surroundings. The best that can be achieved is to reduce the number of times that someone will be dazzled and the severity of those events.
In the case of motor vehicles this is done by expecting that drivers will dip their headlamps for oncoming other road users and by not approving vehicles for use on the road if those lamps when dipped, emit more than 625cd in an offside above-horizontal direction.
In the case of pedal cycles, this is done in Germany by expecting that cyclists will aim their headlamps so as to see the road a sensible distance ahead and not approving any headlamps that emit more than 200cd at 3.5º or higher above the beam centre. (That works in Germany because you're not allowed to ride a bike even in daylight unless it's equipped with approved lights and Germans have a habit of obeying the law. Something different would be wanted here, obviously!)
Neither of those measures are 100% effective because nothing ever can be, but they're both a whole lot better than the anarchy that would reign if there were no limits. Previously, the technology didn't exist to let cyclists dazzle anyone, but that's come on in leaps and bounds, and in the vacancy left by out-of-date, unobserved and irrelevant or non-existent standards, a little bit of anarchy is breaking out.
I think it's best to admit and discuss how we would prefer to address this problem, than to deny it in the hope that our Government won't impose a draconian solution.