I want to apologize for my poor English, but i will give my best to explain and include a lot of pictures for the illustration
First of all, Im not going to explain how j.t. circuit works, or how to make one, for those information you have to look for other sources.
I will explain how to use j.t. circuit with bicycle light and convert it to efficient and relatively cheap source of light.
Ive bought cheapest bicycle light for this project (1 euro) and a small lever switch.