Ways to tint the glasses you already own.
There are three common ways today: a clip that holds tinted lenses on your frame, a larger pair that fits over your glasses, and a second pair made with your own lenses in a tinted form. Each stays at one tint, or changes slowly.
A clip on your frame.
A clip holds a pair of tinted lenses in front of your glasses. Some hold on with magnets instead. With some, you can flip the tinted lenses up when you go inside.
The limit: it is a separate part, and it can get lost.
A larger pair that fits over.
Some sunglasses are made large enough to wear over your own glasses. Some wrap around at the sides, a shape that keeps light from shining in around the frame.
The limit: you wear two frames at once, one over the other.
A second pair with your own lenses.
The lenses you see best with can be made as tinted lenses, to wear as sunglasses. Sunglasses can be made with nearly any lens prescription.
The limit: you carry two pairs and swap them when the light changes.
One tint, or a slow change.
A tinted lens stays at one tint. Your own lenses can also be made in a form that darkens by itself in the sun. That change is slow: most of the darkening takes about half a minute, and clearing takes about five minutes. In a car they do not go as dark, because the windscreen blocks much of the light that darkens them.
The rules for driving still apply.
Whichever way you choose, category 4 lenses are not for driving. Lenses that let through less than 75 percent are not for driving in twilight or at night.
Sources:
- Wikipedia: Sunglasses
- American Academy of Ophthalmology: Taking A Clear Look at Prescription Sunglasses
- American Academy of Ophthalmology: Recommended Types of Sunglasses
- The College of Optometrists, Look After Your Eyes: Driving and vision
- The College of Optometrists: Tints and driving
Other guides
Where Photenic fits.
Photenic is being made for this gap: a tint you set, on the glasses you already own. It is in development.