Is batch 100 still the same quality?
SUNBOND OPTIX / LENS TESTING
The first batch passing tells you the formula works. It does not tell you the hundredth batch will.
A photochromic lens is not a coating with a colour in it. It is a chemical system that has to take in UV, change state, and come all the way back, tens of thousands of times. How well it does that is decided during manufacture. Dye concentration. Imbibing time and oven temperature. Resin lot. Cure schedule. Coating thickness. Every one of those moves, and none of them moves visibly.
Photochromics also have to be measured twice. Clear and activated are two different products wearing the same frame, and a lens can be correct in one state and wrong in the other. Most of what goes wrong in production shows up as a gap between the two.
They fail soft, as well. A cracked lens announces itself. A lens that darkens two shades short of the last batch, or takes ninety seconds to clear instead of forty, passes every visual check in the building. The first person to notice is the customer, who has paid a premium for the one optical feature a wearer can detect unaided.
Then there is the question of which standard the lens is answering to. The same photochromic chemistry ends up in sunglasses, safety eyewear, ski goggles and motorcycle visors, and each of those answers to a different standard. Buyers add their own requirements on top, and a driving scenario is its own conversation again.
Which brings us to the part that gets skipped. A type test approves a design. It says nothing about the batch you are shipping in March, from a different resin lot, through an oven that has been recalibrated twice since. Drift is not a hypothetical, it is the normal behaviour of a chemical process running at volume.
So photochromic performance is not something you verify once. It is something you monitor, batch after batch, for as long as you are making the product. That is easier to say than to resource, which is the real reason it gets skipped.
Our GET.Photochromic tester is built for exactly this. It covers photochromic lens testing before and after activation, plus a special testing function. Its proprietary light source system simulates the testing environment per, and surpasses, ISO 12312-1 sunglasses, ISO 16321-1 safety eyewear, ISO 18527-1 ski goggles, ECE 22.06 motorcycle helmet requirements and special commercial demand such as driving scenarios. Automatic movement with a robotic arm allows high speed testing before and after lens activation. It runs with no water at all, so there is no circulation, no tank and no waste stream to manage.
We think it is the best way to test photochromic lenses, and the strongest argument for that is not the specification. It is that per batch testing stops being a project and starts being routine.
One question for anyone shipping photochromics at volume: do you know how the batch going out this month compares to the one you had certified?
We have been testing lenses since 1989 and we are always glad to compare notes.