What height above the runway is visibility measured?
One would probably have a better view of the runway from a 747 flight deck than a c_152, as regards slant visibility through fog on t/o.
I was once told on three occasions approaching Birmingham in my C-152 at 3am in the morning the visibilty(RVR) was 50m, yet i replied visual with the runway.
Wasn't until i started to roundout that i hit a shallow bank of low mist that couldn't have been deeper than 6 feet hanging just above ruway.
No problem landing with the landing light off.