Just in case my own statement above is not good enough for the non-believers, let me offer the following, which is copied directly from Leupold's website. Pay particular attention to the last sentence:

The Leupold Answer Guide


Advantages of a 30mm Maintube
Does a 30mm maintube give you more light? The principal advantages of the 30mm tube are added strength and increased adjustment range for windage and elevation. For example, the M8-12X (1" maintube) has a total elevation adjustment of 51 minutes. The Mark-4 M1-10X (30mm maintube) has 90 minutes. The percentage of light passing through a scope is a function of lens coating and optical design, and has nothing to do with tube diameter.