This article was published in 2008, in Newsletter 76.
While the evenings may be getting lighter, it is still a good idea to make sure that your bike lights are working before you get caught out. Rather than discussing the pros and cons of the various kinds of lights, David Green takes a look at practical ways you can make your bike lights as effective and reliable as possible.
Front light position
Your front light must be high (up to 1.5 m from the ground) and visible from the front. Try to find a higher less-obscured position than the front fork. Mount the lamp in a central or ‘offside’ (right-hand-side) position. The handlebars are an ideal mounting place, providing a good beam and making it easy to fine-tune the beam as you ride. Make sure that the beam shines almost horizontally. Check this by riding along a quiet residential side street one evening. Well-adjusted front lights have no trouble illuminating reflective car number plates well ahead of you. If you have a basket or bar bag, most bike shops sell brackets designed to fit a light on the brake mounting point on the fork crown. If you are forced to use the fork, go for the highest position you can. PVC tape or a strip of old rubber inner tube around the fork helps prevent the bracket loosening as you ride.
Rear light position
Make sure your red back light is shining towards the following traffic, not down onto the tarmac or into your wheel! Again, find an unobscured position, ideally as far back and as high as possible (between 35 cm and 1.5 m from the ground) where it won’t get knocked or hidden.
Don’t fit the back light close up under your saddle: lights there are easily obscured by jackets without you noticing!
Some models of rear light provide a reflector as well, and fit onto the mudguard. Although a bit vulnerable to damage, this is a good location – provided you have a rear mudguard. Otherwise, unless you have a rear rack, a good position is the rear brake bridge bracket. If you do have a rack, right at the back of the rack is best, where it will be unobstructed by luggage. If there isn’t a mounting point on your rack you can buy or adapt one. Less good positions are the offside of a rack or seat stay, as they are lower and slightly hidden. Brackets provided with some dynamo lights are another possibility, but only if they are designed for right-hand-side mounting.
If you are using standard battery lighting, periodically remove the batteries and check the battery contacts are clean and that they are making good contact with the batteries. The best way to clean the battery and switch contacts is to use an aerosol electrical switch cleaner (such as Servisol, available from Gee’s or Maplin). As soon as the lights start to go dim, replace the batteries. To compare alkaline battery performance, see the test results at www.audax.uk.net/lights/brite994.htm.
There are also many excellent lighting systems based on rechargeable batteries. I recommend Myra VanInwegen’s excellent lighting articles at www.myra-simon.com/bike/tips.html for advice on selecting and making best use of these systems.
Generator (so-called dynamo) lighting
‘Bottle’ dynamos need to be mounted correctly, otherwise they can slip and be noisy. Mount the dynamo so that when it’s ‘on’, the spring pressure forces the knurled wheel in towards the tyre. A position to the rear of the seat stay achieves this (and avoids your heel hitting it as you pedal!). The knurled roller should press flat against a special ribbed dynamo track on the tyre. You may need to make a cut-out in your mudguard to allow this. This prevents slippage and avoids wearing out the side of your tyre. Worn dynamo rollers can be rejuvenated by fitting a rubber cap sold in most bike shops. In the ‘off’ position, the roller should only be about 10 mm away from the tyre.
If one of your dynamo lights stops working, simply ignoring it will soon result in the other bulb burning out! It’s better to stop and change the bulb. Some generators have an electronic regulator to help stop bulbs blowing, or you can buy an add-on one (see Newsletter 22).
If a replacement bulb doesn’t work, check the wiring. Most dynamo systems are ‘single-wire’, relying on the metal bike frame as the ‘earth’ part of an electrical circuit between each lamp and the dynamo generator. Check that the wires make good contact with the light brackets and the dynamo body. Also, make sure that the mounting points of lamps and generator make good metal-to-metal contact with the frame. Paint and corroded fixing points are common causes of unreliable dynamo systems. Replacing original nuts, bolts and washers with stainless steel ones can help. Fitting a DIY twin-cable system is the most reliable.
DIY twin-cable systems
Twin-cable dynamo circuits use a separate cable as the ‘earth’ between each lamp and the dynamo generator. All you need to upgrade your dynamo lights to the more reliable twin-cable system is a soldering iron, a few metres of twin-core cable, some ‘spade’ connectors) and some zip cable-ties (all available from Gee’s, Maplin or other electrical, electronic or DIY shops).
For each lamp, replace the single wire with a length of twin-core cable. Solder on the connectors to each end of one core (‘earth’), and attach them to the lamp and the dynamo mounts. Attach the other core to the same bulb and dynamo points as the single wires you are replacing. Secure the wiring neatly with zip ties.
Be prepared for bulb failure by carrying some spares in your road-side toolkit. A plastic 35 mm film box is my container of choice!* Wrap the bulbs in tissue to stop them rattling around. Front and rear bulbs generally differ, and they come in screw-in and push-in fittings. Typical sizes for standard battery lights are 2.5V, 0.5A, 1.25W. Typical sizes for dynamo lights are 6V, 0.4A, 2.4W (front) and 6V, 0.1A, 0.6W (rear), but yours may differ. If you have dynamo lights, a simple upgrade is to replace the front bulb with a much brighter halogen equivalent. Remember to avoid fitting halogen bulbs with bare hands, as this will make them burn out. A comprehensive source of bulb information is the Reflectalite website www.reflectalite.com/buyingbulbs.html.
*For those who have gone digital, the Editor can supply old film canisters.