LTV (Light Transmission Value) denotes how much light transmits through the lens. Low values are great for sunny conditions, and high values are great for less sun. Photochromic lenses with an LTV range will change their LTV based on the conditions they're exposed to making them perfect for variable lighting conditions without having to interchange lenses.
When shopping for sunglasses the LTV of each lens is listed below the main image section on the sunglasses' product page.
When shopping for spare lenses the LTV of each lens is listed in the "Description" tab on the spare lenses' product page.
Visit our Lens Technology Page for more details