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Make your own cheap, bright headlight

From Newsletter 20 (October 1998)

A constant problem with cycling after dark is the need for bright, reliable and theft-proof (or dirt cheap) lights.

For years now, I've favoured using old-style bolt-on battery lights together with dynamo lights. This gives redundancy and usually adequate light. And as both are bolted firmly to the bike, I've never had a problem with theft. However, more recently, I have wanted brighter lights. The reasons for this are

to be more visible
to be able to see well off the road
to help me detect black-clothed unlit 'stealth' cyclists in winter on my commute across Midsummer Common.

I decided to use a 12-volt system. The obvious lights were the sealed 12 V halogen spot lamps designed for home use, so long as they could be attached to my cycle in a robust manner and did not fail prematurely due to vibration. It turned out that it was possible to construct an entire lighting system for a little less than £10, which made it worth trying.

You will need soldering skills to construct such a light yourself, and I take no responsibility for burnt fingers, burnt bicycles, exploded batteries, etc. Don't take these as full instructions. The critical parts include:

A battery. A 12 V 2.1 Ah (ampere hour) battery weighs about 800 g, and this is what I usually use. It gives less than one hour's lighting, but this is more than enough for my commute. You could use a heavier, higher capacity battery, or a NiCd or other battery if you prefer, so long as it is 12 V, but I recommend avoiding disposable batteries (20-watt lighting would be expensive with these). I bought mine from Greenweld Electronics, a mail-order surplus supplier. They are also sometimes available from Bull Electrical, a similar surplus company, or locally, from Gee's in Mill Road.
The mechanical structure consists of two Jubilee clips and some 40 mm plumbing parts, which are a perfect fit for the lamp. These I bought locally from Ridgeon's.
A fuse - very important. A shorted battery could easily cause a fire.
A Philips Standard Line Halogen Bulb, 12 V 20 W 10° (type no. 6642, aANSI no. ESX). Must have front glass. I have one light with a 36° bulb (more common); this works fine, but I am wary of dazzling oncoming traffic. I recommend pointing the bulb slightly downwards. You get a longer-range light with the 10° bulb, but the wider one may be more suitable off the road.
A charger. To correctly charge a sealed lead-acid battery, you need a voltage-regulated supply. Suitable ready-made chargers cost £20 upwards. Don't use a car battery (or any other unregulated) charger, because this may ruin your battery. Other types of battery need their own special chargers.

The components for the light. Detailed construction notes can be obtained on the Web, by asking nicely at the Campaign stall, or by writing to us - see Contacting the Campaign.

My lights have been in use for six months now and the bulb has not failed yet. I have found that when I am riding fast with the bright light, cars seem less likely to emerge from side streets in front of me, possibly because they are not sure whether I am a cyclist or a motor-cyclist.

Of course, this light is not built to the British Standard, which specifies a tiny bulb powered by small batteries. I find it difficult to believe that a case could be brought that I was inadequately lit with my light. However, I am still an advocate of redundancy in lighting: it would probably be a good idea to have, say, a dynamo set in case the battery runs out, and to make sure your bike conforms to the letter of the law.

David Hembrow