tatfiend 

Does anyone know if the main bulb on this is being fed AC direct from the dynamo or does it go through a bridge rectifier first? I presume that there is some rectifier diode in the light as the light on indicator is an LED even though the main light is a quartz halogen. The electronics inside are sealed in a black box. Certainly no voltage regulation for the main bulb apparently as Shimano fits a 9.5 volt 5 watt Halogen bulb, to keep it from being burned out I presume.

I was wondering as I am trying to figure out if the main lamp could be replaced by one of the Maglight LED conversion modules to increase the light output to something more useful. My LP-R600 was included with a new bike and promptly upgraded to the B&M IQ Cyo Senso headlight to get some reasonable light output.

tatfiend 

I think that I answered my own question. Using a DMM I could not detect any resistance internal to the light other than the bulb. As diodes have some resisteance even in the forward direction it looks like the main bulb is run off of the AC from the dynamo w/o any rectification. Too bad as it makes any upgrade a more involved project. The electronics is apparently one diode and a resistor for the indicator LED which IMO is outrageous for a $50 dynamo headlight.