The LED itself regulates voltage. That's what a diode does.

http://www.merriam-webster.com/dictionary/diode
an electronic device that allows an electric current to flow in
one direction only

It has been many years since my electronics days, but I believe a diode
does have a fixed voltage drop. I think it's around .7 volts if I remember
correctly. So it does regulate the voltage in some respects.

Anthony Watson
www.watsondiy.com
www.mountainsoftware.com