Here are some circuits for using LED's with a dynamo.
http://www.pilom.com/BicycleElectron...moCircuits.htm
The above circuits have been around for a few years now. They also do not require batteries. I personally do not like my headlight and taillight going out when stopped. I added batteries to my system so my headlight and taillight continue to illuminate at stops. These are Ni-MH AA 1,800mA hour batteries. If the batteries are fully charged they will power my lights for at least 3 hours without the dynamo engaged. I selected a Luxeon 1-watt LED rated for 350mA and a 5000 mcd 10mm red LED in my taillight. It's rated for 36mA but I set the current for 30mA with a 100-ohm resistor. My resistor for the headlight is measured at 4.9-ohms. I simply used a 5.1-ohm resistor and parallel 50-ohm resistors until the current through the LED measured with a milliamp meter read 350mA with a fully charged batteries, the dynamo engaged, and riding at 10 MPH where the dynamo is producing maximum current. My resistor consists of one 5.1-ohm resistor and three 50-ohm resistors in parallel. According to the wire used to hook everything up will determine the resistance required for your setup. You'll just need to experiment and find the required resistance for your setup. I chose these components for a reason. With the dynamo engaged, LED's turned on, and traveling at 10 MPH or higher 120mA of excess current produced by the dynamo is recharging the batteries. This is the suggested slow recharge rate for Ni-MH batteries. When you open the LED switch turning off the LED's the full 500mA current will flow into the batteries. This is the suggested rapid recharge rate for Ni-MH batteries so if you completely discharge your batteries you can easily recharge them during the day with your dynamo. This is very handy when touring where you would not have power available or you did not carry a battery charger to recharge them from the utility power grid. I chose to use 4.8-volts with the batteries regulating the voltage to ~5.2-volts as this voltage conforms to USB standards. I installed a USB connector so I could power and recharge a GPS unit with the dynamo and Ni-MH batteries. Here is the circuit I use.
I ordered my 1-watt LED and matching Fraen 10X20 elliptical holder and lens from here.
http://www.luxeonstar.com/index.php
I just put the red 10mm LED in the taillight where the .6-watt bulb was. I built my LED and optics in a 1-inch PVC pipe coupler available in the plumbing section of any hardware or building supply store. A prescription bottle cap with the selectable child-proof/easy open cap is used to hold a clear plastic cover over the front of the lens to protect it. A scrap of aluminum used as the heat sink was cut to fit in the PVC pipe coupler and RTV sealed the rear of the optics and LED.
