Reading comprehension is not what it once was in this country
I understood what the OP was asking on my first read.
Automatic brightness on the Infinity is atrocious. It was just as bad on my Prime. I'd figure they'd have fixed it on the Infinity at least. The slider is dynamic, so it will move on its own as the tablet senses more light on Automatic. The problem is that Asus has not done a good job configuring the settings. My guess is that Asus wants to pad the battery performance of its tablets by dimming the screens to the max unless you are in the sun or next to an overpowering light source, but then you don't get to enjoy the gorgeous screen!! Custom ROMS, like AOKP on my Galaxy Nexus will let you adjust screen brightness depending on your custom light levels.
I just ended up getting an app that controls the light sensor much better. It's called "Lux Auto Brightness"
https://forums.androidcentral.com/e...DEsImNvbS52aXRvLmx1eC5mcmVlIl0&token=PN4Agn7C. They also have a Donate version if you want to reward them for the great app.
So far it works much better than the stock Auto Brightness on my Infinity. And if you find it needs adjusting, you can adjust it to what feels more comfortable for you in different lighting settings, and it's easier to do than it is in a custom rom. Just make sure you disable the Asus auto brightness in lower right if you use Lux.