What are the disadvantages of transition sunglasses?

[Wenona]

When I was in the sunglasses boutique, the salesgirl there strongly persuaded me to buy a pair of transition sunglasses. But I am not sure if it is worth. What are the disadvantages of transition sunglasses?

[Wenonah]

Compared common sunglasses, transition sunglasses, also photochromic sunglasses, made of transition lenses that enables them to activate, or darken, when exposed to the sun ultraviolet light. Besides, the dark lenses can adjust itself in sun rays. The greater the intensity of UV rays, the darker the lenses become. When get the transition sunglasses rid of UV light, the lenses will fade back and turn to clear lenses like regular glasses. what's more, they also provide UV protections. However, the lenses do not change immediately. It takes a few minutes for the lenses to change from light to dark or vice versa. So,these transition sunglasses may not work well when you drive.

[Tom Green]

Though there are many advantages of transition sunglasses, they do have some disadvantages. Transition lenses won't turn cdark completely immediately when they are exposed to the sun light. It takes time for the photochromic lenses to change the color. Moreover, they don't work effectively when you are in a car because the windshield of the car will block most of the UV rays. Thus less UV rays can pass through the window and get into the car. Therefore transition glasses won't turn as dark as sunglasses in the car. That is to say, transition glasses are not suitable for using in the car.