What is the exception applicable to basic VFR weather minimums in FAR 91.155?
CFR 91.155(b)(2) has the exception: 


  (2)Airplane, powered parachute, or weight-shift-control aircraft. If the visibility is less than 3 statute miles but not less than 1 statute mile during night hours and you are operating in an airport traffic pattern within 1/2 mile of the runway, you may operate an airplane, powered parachute, or weight-shift-control aircraft clear of clouds.


So if the visibility is less than 3 statute miles (not less than one statute mile at night), you can operate in Class G as long as you are clear of the clouds and within 1/2 mile of the runway. It does not mean that the entire exception applies at night, only that at night, you need to have at least 1 mile of visibility, otherwise during the day you can operate down to nothing as long as you are clear of the clouds.