Can i darken my sunglasses?

My friend got me a pair of sunglasses (it was a buy 1 get 1 free and she knew i was looking for new ones)

Im not a fan of the frame color but thats not as important as the size and shape and these happen to be just the right size and shape BUT the lenses have a gradual tint that starts medium-light and goes almost clear at the bottom.

My eyes are extremely sensitive to light i get mild sunburns from too much sun exposure these do have a UV treatment so they should be ok but to be safe id rather have them darker the less light that gets thru the better but i still need to be able to see for driving and stuff like that.

Id like to do this the cheapest way possible and at home if possible

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