Lighting question

[Magnified]

I was taking my daughter some where last night and was adjusting the instrument lighting when I noticed the second slider next to it on the right, that has the little "ceiling light" icon next to it. I swivelled it up and down the entire track but never could identify anything changing on the interior lighting. Can you guys clue me in? I thought it was adjusting the interior cabin ceiling lights but it didn't seem to do anything at all.

 

[45-70govt]

 

[Magnified]

Thanks. But when I rolled it up and down last night and looked at the interior cabin lights they didn't change at all. No I'll have to dig into it! lol