Alternator light

Ok, not just a stupid queston.

On the way home tonight, my alternator light came on strong as a approached
a red light. After rpm came back up, the light never fully went out.  Stays
on very very dim. Increases in intensity with rpm.  I have seen this happen
on other vehicles and I can not remember the cause. Any thoughts?

Brent
2 little spridgets, F*rd Escort (little), little dinky row boat ,and
F*rd F150 Supercab 4X4