My first stupid question...cut the flash brightness down a bit?

[JQuill]

The flash is BLINDING lol. When you take a closeup of somebody in a dark room and need the flash it like offends them because the flash is so bright lol. Is there a way to use only ONE of the flash bulbs or cut down the voltage going into the flash so it's not as bright. Not a huge deal, but I am totally ignorant when it comes to the flash, I've been using a Diamond for the past 4 years with no flash, don't know how easy that would be or if it's even possible. Thanks for the help guys.