Dazzling bike lights

The headlamps on cars have also become brighter and augmented by rows of LED daytime running lights. It seems like we’re in a lighting arms race. But thanks to a lack of regulation on our side, it’s an arms race some cyclists are winning! And people are starting to notice.

That’s no bad thing you may think; we need to be noticed more, for safety’s sake. But not when one person’s safety is won at the cost of another’s distress and loss of safety, including other cyclists.

Here’s something that happened to me last winter, riding home through unlit country lanes, I was descending a long, straight and gentle hill when I met a car coming the other way on full beam headlights. They were so glaringly bright that although I have an excellent (no-dazzle Schmidt Edelux) headlamp myself, I couldn’t see a darned thing beyond those headlights. However I was aware of another car some distance behind me, so I thought this approaching driver would surely dip pretty soon for that, if not for a cyclist. He (or she) didn’t. But I know the road well, so I didn’t brake and aimed into the dark just a bit to the left of the offside light. Firstly I noticed this car was going rather slowly, and just had time to think it might be driven by some old geezer who can't find his dip-switch, when I passed and saw not a car, but two cyclists on road bikes steadily pedalling up the hill! I was too surprised and didn’t have time to say a thing. Which was just as well. It wouldn’t have been polite, and they probably don’t realise they were selfishly blinding every person they came across!

The Sunday Times takes an interest

As I get to review things, I’m well aware of how much brighter bike lights have been getting. So whilst it can be fun to make the night as bright as day, that isn’t necessary at sensible night-time cycling speeds and I find some of them downright embarrassing to use, impossible to use responsibly except by cupping one hand over the light at the approach of another road or trail user. And at CTC we are receiving increasing numbers of complaints from the general public and our own members, about the blinding lights used by some cyclists.

At the end of 2012, I was contacted by Alex Pell, a journalist and cyclist who’d got wind of the controversy that was beginning to surround the use of very bright bike lights. He wanted to find out whether cyclists are using these lights irresponsibly, or whether the lamps are simply too bright to be used any other way.

We chose around ten reasonably expensive bike lamps, to represent the market for very bright on-road lighting – as it was in the winter of 2012/13. These ranged from market-leading British-made lamps sold in all good bike shops, to low-cost direct imports available on the internet.

Glare is a subjective matter. It can be measured, but depends upon the brightness of the general scene and position within that scene of the source of glare, as well as its ‘luminance’. Luminance is the intensity of light emitted (in candela) in a particular direction, divided by the area it comes from.

According to the Road Vehicles Lighting Regulations, it is an offence for any light on any vehicle (that includes bicycles) to “cause undue dazzle or discomfort to other persons using the road”*. So the law is subjective too and to put some numbers on how bright a light can be before it’s likely to dazzle, we must refer to design standards.

Standards

Motor vehicles have to be ‘type approved’ for use on public roads, and as part of that approval their lighting must conform with ECE regulations. These ensure that dipped headlamps don’t dazzle other road users by putting a top limit on the intensity of light emitted in an offside above-horizontal direction. For technical reasons different types of lamp have different limits**, but the most another road user should see from any ECE approved headlamp, when dipped, is 625 candela.

When it comes to bike lamps, the British Standard is out of date to the point of irrelevance. Your chance of finding a genuinely BS6102/3 headlamp in a specialist bike shop is close to zero and most of those on the market are simply designed to deliver as much bang as possible for the cyclist’s buck. And that’s no bad thing - until you meet one coming the other way!

Size matters

I hear what you’re thinking: 200 is a lot less than the 625 allowed from a dipped car lamp and that’s not fair! Actually it's very fair, given how much smaller bike lamps are compared to car lamps, which makes them more dazzling for the same candela intensity.

A smaller lamp is more dazzling because each little bit of the lamp’s surface will then be sending more photons into the corresponding rod or cone of the observer’s eye. Once that receptor has been saturated with light, more does nothing useful, only hurts and bounces around inside the eye making everything else look fuzzy. So dazzling is also a complete waste of energy.

Now imagine the same amount of light coming from a larger emitting surface. The image of this larger lamp covers more of the observer’s retina, so each rod or cone is bombarded by fewer photons and does not saturate. And with more of the observer’s nerve cells responding more efficiently to the light you’re putting out, it has more effect. With a larger lamp you’re on a roll. You don’t just avoid dazzling people, but also get more conspicuity bang for your lighting buck!

Simply regulating light intensity isn’t a great way of limiting dazzle. But it’s better than nothing. And given that bike lamps are typically less than a quarter the size of motor vehicle lamps, a lower limit of 200cd is more than fair.

What's your aim?

Since bike lamps cannot (usually) be dipped, and are not fixed in the vehicle, the standards for bike lamps have to make assumptions about how the lamp is likely to be aimed. They generally assume the brightest spot in the beam will be aimed downwards at an angle of 3.5 degrees.

For a lamp on the handlebars, 1m above the road, 3.5° down means that brightest spot will hit the road 16m in front of the bike. And it means the rider won’t be able to see very much beyond that. So I think most cyclists will probably aim their lamps a little higher in order to see further ahead. If you agree, you have to agree that standards are more than fair on this point too.