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A cheap and bright bike light design

My daily commute back in 1998 included a section which was off road and unlit. I needed a brighter front bike light than the Union halogen front dynamo light which I had been using and using available parts at the time I made what was for then quite a good inexpensive lighting system.

2010 update: Enjoy the article for what it is: a glimpse into the past. Technology has moved on. It's really not worth making DIY bike lights any more. For the last year I've been riding with the Busch und Muller IQ Speed headlight. It's a revelation. The lens and reflector shape results in much less wasted light so that this relatively economical to run light will light the way ahead of you very well without dazzling anyone. I did try commercially available LEDs and lenses for DIY, but they don't have the right shape (i.e. they are round, or oval: Not giving the tight pattern of light with a sharp cut off at the top that B&M's light gives) so waste too much light upwards where it dazzles. It's really not worth doing this any more.

2007 update: Please note that this article was originally written way back in 1998. At the time, LED lighting was in its infancy and battery technology was not quite what it is now either. If I was making a light now, I might well look in the direction of LEDs instead of halogen bulbs. MR11 LED lamps are now available and if you can find one with a narrow enough beam, you can follow the design below with one of those and have a considerably longer battery life as a result. I suspect that LED lamps don't get as tight a beam, and that you might want to consider making a wide angle LED lamp to complement the tighter beam of a Halogen. Both can be made as shown below.

Thease days I might also consider an alternative to lead acid batteries. I had to replace my batteries as they became unable to take so much charge.

Having said all that, this light was very sturdy as built and has not failed yet. It was used daily through the winter months for several years, until I no longer had a commute. If you need a cheap and effective light, this is still a good option.

The use of the two crossed jubilee clips (one around the handlebars and one around the light) proved to be one of the best things about this design. They provide a very sturdy way of attaching almost anything to a bicycle and I've used them for other things since.

I've heard from a fair few people who have built lights based on this design and been happy with the results and hope that others can also benefit.

Also note that I have added a few links to my cycle tour stories at the end of this page. Now on with the original article:

I soon decided that an ideal bulb would be one of the 12V halogen spot lamps designed for use inside the home, so long as they could be attached to my cycle in a robust manner, and so long as they were durable in use. It turned out that it was possible to construct the entire light described here for a little less than £10.

The low price is dependent on finding a supply of cheap 12V lead acid batteries ( Mine is from Greenweld and cost a mere £2.50. This company or Bull Electrical usually have well priced surplus cells.

Here in Cambridge, Gees in Mill Road are also good

The mechanical structure of the light consists of 40mm plumbers parts (some of) which (if you get the right ones) are a perfect fit for the lamp itself and need no modification.

You will need to have soldering skills in order to construct such a light yourself, and I take no responsibility for burnt fingers, nor burnt bicycles / exploded batteries etc. The success of such a project is based entirely on one's own skill. Do this at your own risk.

Parts needed

• Osma P/FIT 40mm Universal connector SW102B

• Osma P/FIT 40mm Access plug SW292B

• Jubilee Clip Size 00: 13-20mm

• Jubilee Clip Size 2A: 35-50mm

• Philips MR11 Standard Line Halogen Bulb 12V 20W 10degree. type nr. 6642, aANSI nr. ESX. Other manufacturers are fine, but the narrow beam is much better than the wide one, and you must have the front glass

• 12V lead acid battery

• Fuse

• Switch

• Connectors and wire

The universal connector suggested is the right size to accomodate the bulb. Some alternatives were slightly too small, so take your bulb with you when shopping for this part. Note that these are available in a number of colours. I went for the black one in the hope that it attenuates the light source enough and stops me dazzling myself ( which it does ).

The Jubilee Clips are used to attach the light to your handlebars. This is not an easily removable design. I hope that plumbing on your handlebars isn't too attractive to a thief, though it does look reasonably tidy.

A colleague of mine has built the light with a 36 degree bulb instead. This works fine, but I am wary of dazzling on coming traffic, and you do get a slightly longer range light with the 10 degree bulb.

As already mentioned, surplus lead acid batteries are commonly available. You could use a NiCad or other battery if you prefer, so long as it is 12V, but I recommend avoiding any kind of disposable battery. 20W lighting weould be expensive on disposables.

A fuse is essential. Hopefully placed as close to the battery as possible. A shorted lead acid battery will produce a fire unless it is fused. You'll see how I did this in the battery section below

My switch came from my junk box. Any could be used, I chose to place the switch at the back of the lamp in the access plug, so if you want to do the same, make sure it can easily be mounted there.

I used phono connectors and more wire from my junk box. Phonos can take the current, are cheap and easy to use. I've used these lights for over a year now with no sign of corrosion on the phono connectors, which I smeared with a little grease to prevent this. If you're paranoid about corrosion, gold plated phonos are only a little more expensive.

Construction

Remove one end of the universal connector. This is tricky, you need to pull hard with your fingernails or find some tool to do it. Take care. You then need to remove the rubber seal from this end. The first time, I cut the seal carefully with a Stanley knife until I could get it to keep the bulb exactly in position. I didn't bother refitting the seal at all on further lights. It doesn't seem to matter. Don't put the bulb in yet, it is difficult to get it out again.

Cut holes in the access plug to accomodate your connector and switch. Being sure to put your wire through the universal connector first, solder wires from the rear of the bulb to the switch and connector. You can now assemble the light itself.

To mount the light on your handlebars, you need to first connect the two jubilee clips together. The larger one goes around the light, and the smaller around your handlebars. You either have the light above or below your handlebars. I choose the latter as it means I can still put my bike upside down if necesary to change a wheel / fix punctures etc. without the lamp being in the way.

Next, make up a phono to phono cable ( or use a redundant hifi cable ) and attach the other connector to your battery. Remember to use a fuse! My battery simply rides ina plastic bag in the basket on the rear of my bike. It is a good idea to make sure that the cable is firmly attached so that it cannot come undone while you are riding along.

Battery

I use sealed lead acid batteries. I attach a fuse by using a piece of chocolate block glued to the top of the battery within which I use 5A fuse wire. This is a very cheap and effective way of achieving this, and also allowed connection of wires to a female phono connector while giving somewhere to attach those wires without putting mechanical strain on the terminals of the battery itself. This is an important consideration, as mechanical failure is your most likely problem.

My basket simply sits in my rear bike basket along with my other luggage.

A charger

To correctly charge a lead acid battery, you need a regulated supply of around 13.8 volts.

I used the following circuit. The 7812 is a 12 V regulator chip. You can adjust the voltage it produces by connecting other components between the common pin (pin 2) and ground. My red LED had a forward voltage of 1.6 V, so this made a 13.6 V regulator, which is close enough to the required 13.8 V. All parts were from my junk box, and capacitor values are not critical:

The 7812 requires a small heatsink. A piece of scrap aluminium is fine for this. Just make sure it doesn't run hotter than you can hold onto.

To supply the input to the circuit I have used at different times either a set of solar cells or a car battery charger. While car battery chargers are also rated to charge 12 V batteries, they rely on the huge capacity of a car battery to restrict current and voltage and you must use a regulator like this to protect a smaller lead acid battery from damage from a car battery charger.

I now have many other cycling articles on the web, which include tour stories and reviews of bikes. Click here for a list which include the following:

Back in 2000 we toured Lincolnshire.
In 2002 and 2003 I went on a cycle racing trip to the Netherlands.
In 2003 we went on a cycling holiday with the children in the Netherlands.
In 2005 we visited the Dutch national cycle museum.
In 2006 I cycled from Land's End to John O'Groats.
We now live in the Netherlands and arrange cycle tours.