This is most probably the cheapest bike light ever made, aside from those that involve just sticking a torch on your bike. I had most of the parts lying around and I tried to recycle much of the stuff I used to make this. The only significant expenditure in this project was the pseudo Luxeon 1W which gives a decent amount of light for significantly lesser cost than an actual Luxeon. Pretty much anyone should be able to make this.

Step 1: Parts

El cheapo 1W luxeon.................................Rs 60
Heatsinks......................................................Rs 15
Switch (SPDT)..............................................Free
Foam (Stiff / soft)..........................................Free
Zip Ties.........................................................Rs 50/100 ties
Wire...............................................................Rs 3/m and 1.5 metres used
Solder
Soldering iron
Tape
Fevibond
cardboard shampoo box
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Total Cost...................................................~Rs 100=< 2 dollars !!!!

Step 2: Setup of LED

Attach the LED to its base and solder wires to it. Affix this to the heatsink and attach the heatshink the stationary section of a door bolt. This will help in anchoring the LED to the foam. Cut the soft foam to accomodate this arrangement and cut the stiff pieces of foam to act as reinforcement as shown in the picture. (Blue=stiff, white=soft); Affix all the sections of the light to resemble that shown in the first picture.

Step 3: Battery Arrangement

For attaching the battery two stiff pieces of wire were used to shape it into two loops. Since the terminals of the battery are recessed into the battery, a simple wire secured with tape cannot be used to hook up wires to it. Hence two wires as shown in the hand drawn diagram can be used to attach the wires to the battery, as it'll function similar to the spring loaded contacts which are present in the phone. With enough tape and zip ties this arrangement is stable enough to withstand the shocks sustained while riding and has held up remarkably well even while hopping on and off messed up foot paths.

Step 4: Final Assembly

The wires from the LED were attached through an SPDT switch to the battery.

Step 5: Attaching to the Bike

My initial plan was to attach the LED in the position shown in pic 2. But the wires blocked the light and gave distracting shadows. Hence I moved it to the new position on the handlebar. I used a hood made from the cardboard shampoo box to prevent the light from blinding oncoming traffic and gave the arrangement a slight dip. It also helps by not blinding me as some light also escapes upward. The light was secured using zip ties to allow for alter adjustments. The switch was attached to the handle at the position shown and the battery was stored in a pouch i attached below the top tube- seat tube intersection.

Step 6: Conclusion

The main aim of this project was to make a light that makes the bike visible to oncoming traffic and provide sufficient amount of light to navigate a pitch dark road........ just enough to see what's right in front of you. It is by no means a replacement for the many high powered LED instructables that are abound on this site. I wanted to keep costs down and see what the bare minimum can get you and for that I am quite satisfied with this arrangement. I have ridden it over rough terrain and it doesn't flicker, nor does it shift its position around on the handlebar. And I expect the battery to give a runtime of atleast an hour (its and old battery that hasn't been used in a year). And when its used up I just use the phone to recharge the battery :)