Sunglasses too dark to drive...

[21TonyK]

Discovered something today. Sunglasses are categorised by the amount of light they allow through on a scale of 0 to 4, 4 being the darkest as found on some sports/cycling glasses. The number is printed on the arm of the glasses.

Its illegal to drive wearing category 4 glasses.

My bog standard sunnies are a 3, yours?