Gen light stays on until I rev up the engine???

[Bartenfeld]

OK...the belt is tight and the wires are hooked up right. But when I first crank the engine my gen light is on and it stays on until I give the engine a good rev. and I mean a pretty good rev. (i dont have a tach so not sure of exact rpm, but pretty high) After the light on the dash goes off the headlights brighten up and I have never had battery problems, which indicates to me that the alt is charging prop. My question is, what could be the reason I have to "ramp" up my alt before the I can see a change in the electrical system. Could it be a voltage regulator problem?? or does this situation simply point to a bad alt???