The starting point for freeform production is a semi-finished lens, also known as a puck due to its resemblance to an ice hockey puck. These are produced in a casting process that is also used to manufacture stock lenses. The semi-finished lenses are produced in a casting process. Here, liquid monomers are first poured into moulds. Various substances are added to the monomers, e.g. initiators and UV absorbers. The initiator triggers a chemical reaction that leads to hardening or "curing" of the lens, while the UV absorber increases the UV absorption of the lenses and prevents yellowing.
1) What are the photochromic lens?
Photochromic lenses are made of many lens materials including plastic, glass or polycarbonate. They are typically used as sunglasses that conveniently switch from a clear lens indoors, to a sunglasses depth tint when outdoors, and vice versa.
They typically take around 30 seconds to fully darken and approx 2 - 5 minutes to return to a clear state.
2) The advantages of the photochromic lens?
① Reduced costs – buying a single pair of dual purpose photochromic glasses that can provide vision for both indoors when clear and providing sunglasses protection outside is more cost effective than buying two separate pairs.
② UV protection - Photochromic lenses provide full protection against the harmful UV rays of the sun and direct exposure to sunlight can cause serious eye problems and in some cases blindness.
③ Convenience - You only need to own 1 pair of glasses for both indoors and outdoors in the sun as opposed to needing to switch between 2 pairs of regular glasses to sunglasses. You only need to remember to take one dual purpose pair of glasses with you as no doubt at some point we have all forgotten to take our sunglasses out with us only to be caught out by the glare of the sun or even left them behind never to be seen again.
④ Eye Health – Reducing your exposure to the suns harmful UV rays can lower the risk of cataracts or other eye/age related problems