Polycarbonate Polycarbonate (PC) is a thermoplastic, and is by far the most commonly used material in the safety eyewear industry. It is quickly growing in popularity for the prescription business as well. It possesses superior impact resistance (about 10 times that of glass and some other plastics) , it's inexpensive, and it also inherently blocks 99.9% of UVA/UVB rays without any extra or special coatings. PC possesses a higher refractive index at 1.59, which makes it useful for prescriptions. It also accepts add-on technologies to result in photochromic or polarized lenses. PC's biggest drawback is its low scratch resistance. Lenses are usually manufactured with a special scratch resistant hard coat to increase their tolerance. Although it is possible to find safety eyewear with uncoated lenses, they are usually not the preferred choice. Polycarbonate, a generic term, is sometimes referred to by a brand name (though rarely in safety eyewear), the most well known being Lexan.
PlutonitePlutonite, in basic terms, is a purified polycarbonate. A proprietary material by Oakley, Plutonite is used in all Oakley-made lenses. Impact and scratch resistance are similar to those of PC, but the clarity is far superior, rivaling that of the clearest optical glass available. The material also provides 100% protection from UVA, UVB and UVC rays.
Plastic There are various types of plastics used in lower priced novelty and consumer sunglasses and, therefore, various levels of thickness, impact resistance, clarity, and overall quality. We won't elaborate too much on these types as they are not seen in the safety industry. One type, however, that is often grouped with the plastics is CR-39. This is still commonly used -- not for safety, but for sunglasses and prescription eyewear.
CR-39 "CR-39" is simply the name of the resin, "Columbia Resin #39", developed in the early 1940's. The polymer has very good scratch resistance, but remains a relatively soft material -- too soft to pass ANSI Z87.1 impact tests. It also offers very good optical clarity and is still commonly used in sunglasses. It can be used for prescriptions, but its relatively low refractive index (1.498) requires thicker lenses for stronger magnifications. Its use in this application is decreasing with the emergence of the more impact resistant polycarbonate and, in particular, the Hi Index variety.
High Index It is so called precisely because of its higher refractive index, usually 1.60 to 1.74. This higher index means that stronger prescriptions are made possible even with a thinner lens. This is appealing for wearers who prefer a smaller, lighter set. The material is basically a special polycarbonate, and pretty much only used for prescriptions, especially stronger prescriptions. Because of its thinner nature, this version of PC probably would not stand up to high impact as well as its thicker relative, and will likely never become common in the general safety market.
NXT/Trivex NXT is a proprietary material made primarily of Trivex, an advanced polymer that possesses the benefits of polycarbonate, but also has superior optical clarity, scratch resistance and photochromic performance. Trivex is the newest player in the game and, if more eyewear manufacturers catch on, it has potential to be the star and MVP for a long time in the safety, fashion and prescription markets. Arguably the one area where Trivex will likely watch from the sidelines is in the case of stronger prescriptions. Its lower refractive index would require a thicker lens than that of PC or High Index.
Glass Optical crown glass still exists for specific purposes, but is now rarely used in general eyewear applications since the emergence of optical quality "plastic" substitutes such as polycarbonate, CR-39, and Trivex. The two redeeming benefits to glass lenses are excellent clarity and superior scratch resistance. Unfortunately, its two biggest drawbacks, shattering and weight, tend to cancel out those advantages. Of the common lens materials, glass is by far the most prone to shattering, thus creating a significant safety hazard. To decrease the likelihood of a shatter, glass lenses are sometimes made thicker. Already more dense than plastic, a thicker glass lens becomes about twice as heavy as a plastic substitute, and is still not shatterproof. Additionally, the refractive index (1.52) is such that strong prescriptions also require a thicker lens, further compounding the unfavorable weight problem.
Proper Cleaning MethodsWhen possible, lens cleaning should be performed using cleaners specially formulated for use with polycarbonate. Click here to view our recommended cleaning and anti-fog solutions.
Many safety glasses and almost all sunglasses that SafetyGlassesUSA.com carries come with a microfiber carrying pouch or cleaning cloth. This is a universally used material in the eyewear industry, as it has proven to be very effective in cleaning polycarbonate lenses without scratching them. Your eyewear will also last significantly longer if stored in this pouch when not being worn.
Note: It is always a good idea to blow loose and excess debris from both sides of your lenses prior to wiping with any cloth. This will not only reduce the risk of scratching your lens, but also will help to keep your cloth cleaner.
With cloth in hand, carefully wipe dust or debris from your lenses. Moderate pressure is acceptable with a clean cloth and usually sufficient for stubborn spots or smudges.
If you don't have immediate access to the ideal and preferred microfiber cleaning cloth, carrying pouch, or our individually wrapped lens cleaning towelettes, you may still clean your lenses in two ways.
Run water over the dirtied lens(es), both front and back, to wash away debris. Gently dry with a clean, non-abrasive cloth, with slow wipes in a single direction.
If water is not available, forcefully blow away excess debris from your lenses. Then use a clean, non-abrasive cloth to gently wipe away remaining debris. This method should rarely be used, and only be done on the outer side of the lenses, as these are more commonly manufactured with a scratch-resistant coating.
Cleaning Materials vs. Polycarbonate The use of solvents which are not compatible with polycarbonate can result in the softening, crazing, and/or cracking of the plastic part.
Solvents & Cleaners Usable with Polycarbonate:
- #1 & #3 denatured alcohol- 10% Sol Bon Ami- 2% Sol. Reg. Joy- Dirtex- Ethanol- Freone TF and TE-35- Heptane- Lacryl PCL-2035 polycarbonate cleaner- Methyl, isopropyl and isobutyl alcohols- Mexane- Mild soap and water- Mineral Spirits (Paint Thinner)- Petroleum Ether - 65° C boiling point- Varsol No.2- VM and P Naphtha- White Kerosene
Solvents & Cleaners NOT TO BE USED with Polycarbonate:
- Acetone- Agitene- Ajax- All Liquid Detergents- Benzol- Carbon Tetrachloride- Chlorinated Hydrocarbons- Diversol- Gasoline- Kleenol Plastics- Lemon Joy (phosphate free)- Lestoil- Liquid Cleaner - 8211- Lysol- Methyl Ethyl Keytone (MEK)- MIBK- Oils- Pink Lux (Phosphate free)- Stanisol Naphtha- Texize-8006, 8129, 8758- Toluol- Trichlor- Triclene
How do they work?
THEN: When photochromic lenses first came into existence in the 60’s, only glass lenses were used. The embedding of molecules (usually Silver Chloride) was the most common means of achieving the desired effect. Exposed to UV rays, these molecules would undergo a chemical reaction, change shape, absorb some of the passing light and cause a darkening result.
NOW: Since polycarbonate and other “plastic” lenses have become the dominant material in the sunglass world, a slightly different process has taken over the darkening job. The size and shape of the carbon-based molecules (organic) now used are temporarily changed with UV exposure. These photochromic molecules can also be affected by significant variations in temperature, which can be both good and bad*.
Light-Dark Range:The lightness or darkness of a lens is typically measured by its VLT. Visible Light Transmission is how much of the 100% available white (visible) light passes through the lens. This is identified by the percentage.
If we see 100% of the visible light when not viewing through glasses, we may only see 80% of that same light when looking through a typical yellow lens. Through average Gray lenses, we may only see 12% of the same light. It may seem lighter than 12% because our pupils have dilated behind the dark lens to allow more light in.
Of the photochromic styles found on SafetyGlassesUSA.com, the range of VLT for lenses in their light or natural state is 33 to 87 percent. That is, some lenses are nearly clear in their lightened state, while others only get as light as 33% VLT. The VLT range for lenses in their fully darkened state is 9 to 25 percent.
Any Photochromic Problems? Despite all the benefits of photochromic lenses, there are some potential drawbacks to be aware of.
*A) As stated earlier, the organic molecules used in today’s lenses are also sensitive to temperature. But they’re affected in a way that’s probably opposite from what most people would guess – or want. Photochromic lenses will tend to become lighter when warmer and darker when colder. Thus, if you’re in Arizona in August and are desperately in need of dark sunglasses, you’ll need to consider that the 110 temperature that tends to lighten the lens will conflict with the intense UV rays that want to darken the lens. On the other hand, you might find that your glasses are much more effective than you expected on your Alaskan vacation.
B) The effectiveness of photochromic lenses can be reduced or eliminated when used in some vehicles.
To view or purchase our Photochromic Eyewear please visit our Photochromic Eyewear section.
On all the bifocal safety eyewear we carry, the integrated lens is fused on the inside (face side) of the primary lens, thereby preserving the original smooth, continuous look and feel of the main lens, while reducing the likelihood of scratching. Bifocal Safety Glasses are perfect for those who need reading glasses but also require the protection of safety glasses. With Bifocal Safety Glasses you no longer have to swap between safety glasses and non-protective reading glasses to read or see fine details, which is both a safety hazard and a hassle.
All Bifocal Safety Glasses found on SafetyGlassesUSA.com are available in diopters ranging from +1.50 to +2.50, and many also offer +1.00 and +3.00. The PIP Eva bifocals for women are even available in smaller increments for your precise needs.Safety Bifocal options are available in tinted lenses as well, including Amber, Brown, Gray and Indoor/Outdoor. All "safety" styles feature shatterproof polycarbonate lenses, are ANSI Z87.1-2015 certified and provide 99.9% UVA-UVB protection.
What is polarized light? All reflected and refracted light has some degree of polarization. That is, the oscillating waves move across one (or few) plane(s) versus the infinite planes light waves would usually travel in.
The scenario most people associate the polarizing effect with is reflection off a horizontal surface, such as a lake, road, snow on the ground, or other traffic. When reflecting off a relatively smooth surface, especially one that is more or less horizontal, those light rays become horizontally polarized and, with a couple other laws of physics at work, they create the unpleasant glare.
How do polarized glasses work? A polarized lens includes a polaroid filter, one that is vertically aligned. Much like vertical Venetian blinds would block a large portion of light, this more selectively, but effectively, blocks the glare-causing horizontal rays from passing through the lens.
Effectiveness of the lenses can vary, depnding on:
- The angle of incident (the direction of the light source in relation to the surface hit with light.- The surface material causing the reflection.- The angle of your lenses in relation to the reflection or glare.
Why is this important? Glare from reflected sunlight can be dangerous because it is an intense light that is difficult to avoid. We know not to look directly at the sun, but sometimes we must look in glare's direction. Such is the case when driving and blinding glare is dead ahead.
Warning 1: Reflections and glare are how we most easily identify ice patches on the road. With polarized glasses removing the glare or reducing the apparent reflected light from that surface, ice could be difficult to see.
Warning 2: Some instrument panels and displays may be more difficult to read with the use of polarized lenses. Drivers should take care to know which displays cannot be easily read in the vehicles they drive.
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