Consequently, these lenses can change color even on overcast days or indoors. 2. Principle of Color Change It is well established that sunlight carries ultraviolet radiation, which can be harmful to human health. The mechanism behind color-changing glasses involves an automatic adjustment in lens tint depth in response to UV exposure, thereby safeguarding the eyes. Specific chemicals within the lenses undergo a chemical reaction when exposed to UV light, leading to a change in lens color. This means that as long as there is UV irradiation, whether from direct sunlight or ambient indoor lighting, the lenses will adjust their tint accordingly. When driving, it is important to note that the front windshield of a vehicle filters out most UV rays. As a result, the color-changing lenses may not darken effectively because they require unobstructed UV exposure to function properly.