The basic idea to make such kind of USB based device is to utilise the USB power of the computer to lit up the 0.2W LED so that we can get descent light while while operating the laptop /PC .The power output from the USB port is of 5V,500ma current, what we made is that directly used this voltage for the LED alongwith one register.The present design is without the battery. The next modifications in this circuit is to develop a rechargable circuit so that we can charge the li-ion batteries and can be used as power source in case of emergency when there is no power.