I pretty much have that setup in the sense that I have the SON 28 Dynamo and the PedalPower+ Super-i-Cable but I charge devices such as my phone and my Garmin Edge 800 not "normal" battery light. I suspect with the light you need to check the required input. Can you for example charge it via your computer? If yes, then I suspect that the PedalPower+ SUper-i-Cable will handle it as well.
The output for the PedalPower+ Super-i-Cable is given as 5v up to 1000mA. I will scan the owner's manual and link to it from the review link above. Might help answer your questions.