F.A.Q.


What is the difference between CR-39 and polycarbonate?

The CR-39 is a thermosetting polymer (it does not melt if heated) and does not require anti-scratch protection treatments. It is widely used for ophthalmic lenses because of its high optical qualities.
Instead, polycarbonate is a thermoplastic material (it melts if heated) and requires an anti-scratch protection treatment. Polycarbonate is relatively unstable and subject to problems of stress craking and migration, which does not make it very compatible with acetate or metal frames.
Between the two materials, the CR-39 demonstrates a superior optical quality.


Are CR-39 and polycarbonate lenses produced in the same way?

CR-39 lenses are produced through polymerization (the slow transformation of a liquid into a solid reticule) in glass moulds with very long solidification times (about 20 hours).
Polycarbonate is produced for injection moulding in metal moulds.
This process identical to the one used for injected plastic frames, permits shorter moulding times but causes the formation of internal stress.


What requirements must a lens have for "general use"?

A lens for "general use" means normally a product that does not need specific instructions regarding normal conditions of use. In particular, it must be suitable for driving.


What is the most appropriate filter that can be mirrored?

Aside from glass, both polycarbonate and CR-39 can be mirrored without any problems. The results regarding the adhesion of the mirror coating to the base surface, depends how carefully the treatment is carried out and not on the type of material used. In the specific case of CR-39 it is preferable to use mass tinted filters.


What is anti-reflection treatment used for?

Anti-reflection treatment can be applied to both sides of the lens or only internally.
The internal treatment is used to eliminate annoying reflections that appear on the surface and disturb vision (the phenomenon occurs especially with unwrap-around frames and when the user has the sun behind him).
The external treatment is useful in the case of clear filters (usually ophthalmic) to reduce further internal reflections; thus the person looking at the sunglass wearer can perfectly see his eyes.


What are the necessary requirements that make a good quality anti-reflection treatment?

An anti-reflection treatment is of good quality if it shows a reflection degree lower than 1.5%.
The flatter the reflection curve the higher the quality.


The pros and cons of a mass coloured lens.

Advantages:
Disadvantages:


Is infrared radiation hazardous?

It is a well-known fact that infrared solar radiation is not hazardous.
Infrared radiation can cause eye damage only if it is of strong intensity, as when exposed to particular artificial light sources (such as during welding processes or in the proximity of melting metal).


How is it possible to understand whether a lens has UV400 protection?

In order to verify this, it is essential to have a scanning spectrophotometer.
The normal UV measuring equipment is only capable of establishing if a filter gives at least partial protection from ultraviolet radiation, but its low sensitivity is insufficient for verifying total protection up to 400 nanometers.


Why is a melanin lens better than a UV400 lens?

Besides obtaining UV radiation protection, a melanin lens also permits the progressive absorption of Blue-violet light, achieving an excellent balance between maximum protection and the natural vision of colours.
It is known that Blue light is responsible for accumulative and irreversible damage to the eye.


Can de-centred lenses be mounted on any frame for Base 8?

De-centred lenses are usually optimised for certain types of wrap-around frames and allow for their use within an estabilished range. Excessively or slightly curved frames require specific de-centred lenses in order to be in conformity to the requirements established by the standards.


Why does the CR-39 not require anti-scratch treatments?

Because it is already a polymer that has a high scratch resistance which is more than sufficient for normal use.


Why does PC always need anti-scratch treatments?

Because it is a thermoplastic material that has very low abrasion resistance, which is insufficient for any type of use.


Why is acrylic considered to be lower in quality than PC?

Because even though it is a thermoplastic material, it has the same disadvantages as polycarbonate, but not its advantages (high mechanical resistance).


What is the difference between a photochromic filter in glass and one in CR-39?

Photochromic material is completely different and so is its reaction to light. In particular, the mechanism determining the darkening is sensitive to different parts of solar radiation. The plastic photochromic filters darken as a consequence of Ultraviolet radiation, while glass photochromic filters are sensitive to a part of visible light.


Can photochromic filters be "activated" in the car?

Normally the activation is very low, since most of the photochromic filters are activated by UV radiation, which is attenuated by car windows.


Polarising treatment: How does it work and what is it used for?

This is a special treatment that allows light to be filtered according to the polarisation axis.
Its fundamental purpose is to eliminate the reflections originating from horizontal surfaces (water, asphalt, etc.)


When can filters be considered to be within "standards"?

Usually a filter is considered within standards when it conforms to the reference standard existing in the country of destination.
Very often only filters not possessing limitations referred to their use (for example, not suitable for driving) are considered by manufacturer conforming with the standards.


Food and Drug Administration (FDA): What has to be done in order to avoid problems with customs in the USA?

If unshaped lenses are exported it is sufficient to enclose the Drop ball test certificate. If instead shaped lenses or sunglasses are exported, registration with FDA is required.


What is the new requirement regarding lenses suitable for driving (Tmin 500-650nm) inserted in the ANSI Z80.3 standards used for?

It is used for guaranteeing a correct vision of light sources with a very tight band, like for example, led diode signals (lights with red signals) included in some car dashboards or in the stoplights. It is also used for not softening particular artificial lights too much (such as, the lights used in tunnels).


Are the Australian regulations for sunglasses obligatory?

Yes.
Any pair of sunglasses sold in Australia must conform to the AS1067.1-1990 standards. For the moment, part 2 (AS 1067.2-1990) remains as optional.


Can a product that is in conformity with the 89/686/EEC European Directive be commercialised in Australia without further requirements?

No.
In order to be commercialised in Australia it is necessary for the product to be in conformity with the AS 1067.1-1990 standard and to possess the specific information required by this standard (different to the one required by the European standard).


Is it obligatory to include in the package the symbols identifying the filter categories?

No.
European Standards do not require these symbols even if they are very common in some European countries.


Is it necessary for the lens manufacturer to have the FDA registration number when exporting to the USA?

No - because unshaped lenses are not classified as "medical devices", since we are dealing with a product that is not destined to be sold directly to the consumer, but requires further work. It is a different situation if the lens is already shaped into its final form. In this case, it is necessary to register with the FDA and nominate a legal representative in the USA.