Ambiant vs Surface temps?

[Vengeance]

Here is a question that I've been curious about for a while, what temps are more important, surface temps or ambiant temps? When people talk about day and night cycle in terms of temps they allways refer to the ambiant air temps. But when people talk about heat gradiants, I assume they are talking about surface temps. So if you are trying to day and night cycle your snake do you only need to lower the ambiant temps or both the ambiant and the surface temps?

I'll use my setup as an example. I allwasy make sure that the surface temps on the hot side are 90 - 95 and I allways make sure that the surface temps on the cool side are 80 - 85. But for ambiant temp I allways get keep it in and around 85 through out the cage. I don't cycle my Ball because I never inteand on useing him in a breeding project. But I am going to be picking up a pair of Ball's that I will be starting a breeding project with and I know day and night cycleing is imparative for breeding purposes. I'm going to create a tempature controlled room where the ambiant air will allways be 84o F and just use 1 UTH to get a hot spot of 90 - 95. But I'm curious to know if when I day and night cycle, does only the ambiant air temp need to change or the surface temps as well?