My 93 ls400 has done this for the past 8 years. It is especially noticeable when the blower fan is at max speed. Is there a ground point that needs attention? Battery is in good shape as the car starts up instantly. I've gone through a couple batteries since I've owned the car and it has always done this no matter how new or old the battery was.

Chad

 

I found this related post -

https://www.clublexus.com/forums/ls4...s-dimming.html

most everyone who replied said it happens on their ls as well...