An important note about photochromic lenses:
Because they react to UV light and not to visible light, there are circumstances under which the darkening will not occur. Frist example, is in your car. Because the windshield blocks out most UV light, photochromic lenses will not darken. Second,is indoors test with ordinary lighting(Because the lighting used in daily lighting does not contain ultraviolet light),photochromic lenses will not darken.
So the ways to activate photochromism is:
Exposed to UV rays, as in direct sunlight OR Use ultraviolet light lamp (not ordinary lighting lamp).This is the way to activate the photochromic function of the product.