Lights dim at idle

[cain1234]

My 48 Buick has recently developed a "new" problem. With the engine idling, all lights dim noticeably. When I depress accelerator, lights brighten up to "normal". I have recently purchased an Optima Red Top premium battery that I am convinced is not the problem (cranking motor works, horn blows, etc.) Also, about a year ago I replaced the generator with a 6 volt alternator. As above noted, this is a recent problem. Any ideas, solutions (other than increasing idle to 800 rpm) would be greatly appreciated. Thanks,
Charlie Cain
North Texas

[old-tank]

Charlie
Record the voltages at idle and when revved and check back with the numbers.
Willie

[d2_willys]

Voltage regulator could be on the way out. BTW: Have you added any new accessories that might be dragging down the alternator at idle?

[First Born]

Charlie, Willie [old tank ] has good advise. I would carrie it a little farther. Check the voltage at battery, at lights and at alternator, at idle and reved up, with lights on and lights off. The problem is most assuredly a voltage problem. Have you rechecked that cables are clean and tight at battery? Did this happen soon after installing the optima.
Keep us informed.

Ben