On which type of day do most photochromic lenses appear the darkest?

Most photochromic lenses appear the darkest on a cold, bright day due to the way they react to different temperatures and light conditions. Photochromic lenses contain special chemicals that darken in response to ultraviolet (UV) light.

On bright days, there is an abundance of UV light, which triggers the lenses to darken. However, temperature plays a crucial role in their effectiveness as well. When the temperature is colder, the reaction that activates the dye in photochromic lenses is enhanced, allowing them to reach their maximum darkness. In warmer temperatures, the chemical reaction tends to slow down, which means the lenses may not darken as much, even in bright light.

The combination of cold and bright conditions maximizes the activation of the photochromic chemicals, resulting in the lenses appearing their darkest. Conversely, on warm or cloudy days, the reactions can be less efficient, leading to lighter lens coloration.