How does transition lens change in the sunlight?

[Karma]

Is the special chemical material that make it change color?

[Thalia]

The transition lens contains a substance which is called silver halides. This kind of substance will change the color according to the strength of the light.

[Willa]

There are some chemical material which are sensitive to UV rays in the lens such as silver halides and other Copper oxide catalyst.Silver halides would decompose to many tiny black particle under lights and spread evenly in the lens.That's why the lens get black.