How can I check the photochromic technology of my lenses is working properly?

At Julbo, photochromic treatment is applied throughout the body of the lens by casting at moderate temperatures. When in contact with UV light, the photochromic particles are activated in 20 to 30 seconds. If you're not sure, cover one of the lenses with your hand, then put the sunglasses on, wait 20 to 30 seconds and check the difference between the activated and non-activated lens.