Eye o dine?

[sandeepgoodbole]

It is said that Iodine Crystals are responsible for the Polrization of Light.

1How Photon-Atomic Kinetics work in case of poloroid ?
2.Why only Horizontal glare is considered as Nuisance? Are there no glares in every other direction ?
3.If the Poloroid Lenses are fitted to absorb vertical rays( 90 dig. to usual way) wouldn’t that be equally effective?
( In India, we always use fitted as the past tense of fit , B& L had also written so.)

[Pete Hanlin]

I don't know much about the properties of Iodine...

As to why horizontal light is chosen for elimination, most of the surfaces that pose a glare problem (water, dashpads, windshields, etc.) are horizontally oriented. Unless you are climbing ice cliffs, there just aren't usually that many vertical surfaces that pose a glare problem.

[Darryl Meister]

A typical Polaroid film is made by stretching a thin sheet of polyvinyl alcohol and soaking it with iodine. The polyvinyl alcohol sheet is first stretched, which aligns its molecular structure into long, parallel chains running in the direction of the stretch. (Imagine stretching a net of some sort; all of the holes in the net become elongated.) The sheet is then soaked with iodine, and the iodine molecules attach themselves to the long chains of molecules within the sheet of polyvinyl alcohol. This causes light vibrating in one direction (e.g., vertical) to be absorbed when passing through the Polaroid film, while light vibrating in a perpendicular direction (e.g., horizontal) is transmitted.

Best regards,
Darryl

[sandeepgoodbole]

Originally posted by Darryl Meister
A typical Polaroid film is made by stretching a thin sheet of polyvinyl alcohol and soaking it with iodine.
Darryl

Is that the raeson why those are always tinted?
How Poloroids in Glass/CR are created? Puttng the porloroid film btn 2 Lenses or by Treating Cr with Polyvinyl alcohole + Iodine?
I wonder how temperature for Fusing the Poly film in btn 2 Glass Blanks does not harm the film? It must be some other method of arrenging platoons of Iodine inside the glass.

[Pete Hanlin]

Actually, they use a polyvinyl/iodine soaked film in glass lenses as well (which is why you can't heat treat polarized glass lenses- it destroys the film layer).

I'm not positive about the manufacture of plastic lenses, but in poly lenses the film is usually submersed into the liquid resin. In the past, there was occasionally a problem with a polarized lens "delaminating" (dividing back into the individual layers). This doesn't seem to be a problem anymore.

One problem with polycarbonate polarized lenses (which are what I wear, actually), involves the flexibility of the polycarb. If the lens is mounted even slightly too tightly in the frame, the "stress points" will become all too evident in the form of arcs that run along the edge of the lens.

[Pete Hanlin]

There is an article on the manufacture of polarized lenses on page 88 of the Feb 2002 edition of 20/20 (Polar Process- A look at how prescription polarized lenses are made by John Young).

To summarize the article (since I'm not sure everyone can put their hands on a copy of 20/20), Polyvinyl Acetate (PVA) is heated and stretched to five times its normal length before being soaked in an iodine solution. "The iodine forms a long grid of parallel, darkened lines. This grid is not visible to the naked eye but it acts in the same manner as the thin wire grid invented by Hertz in 1888."

The resultant tinted sheet of PVA is then sandwiched between two layers of Cellulose Acetate Butyrate (CAB). For prescription lenses, this sandwich is imbedded into the lens material.

This is basically the same info that was contained in this thread already, but for those who can get a hold of the magazine, there was an illustration and some further explanation of the process.