2. When there are UV rays or sunlight, the transmittance of the photochromic is less than 50%. There are mainly two types ofphotochromic lens, gray ones and brown ones. These two types of lens can block more than 50%, usually 70%, visible lights outdoors. Outdoors photochromic lens (http://www.finestglasses.com/
3. Photochromic lens has the function of UV protection. In the manufacturing process, certain amount of ultraviolet absorbent are added to the lens, and thus the lens itself is equipped with the function of UV protection. In addition, photochromic dye works based on the UV rays it absorbs. In a word, the ability of UV protection is not bad.
4. Photochromic lens changes its color quickly. Usually, a photochromic lens placed in the sunlight for about 1 minute, the transmittance of the lens will decrease at least 80%; when placed indoors for about 2 minutes, the transmittance will return to over 60%. The time that eyes need to adapt to the light is shorter than that of the lens that needs to change its color.
5. The photochromic lens has a long life span. The life span of a photochromic lens consists of two parts: one is the life span of the lens material itself, which is required to be as long as the common resin lens; the other is the life span of photochromic dye consisted in the material of the lens, which is required to be longer than that of resin lens. Generally speaking, if the technology matures, the life span of a photochromic lens is about several years.
6. Photochromic lens is sensitive to temperature. Currently, all the photochromic lenses are sensitive to temperature, which means the lens will change its color quicker at a higher temperature;
7. The speed that the photochromic lens changes its color has something to do with the hardness of the lens. In general, the harder the lens is, the longer the lens will take to change its color. It is not bad for photochromic lens to change color quickly; however, it is not good for lens to be too soft for the softness will influence its life span. The softness will deform the lens.