QUALITY OF EYE GLASS
Index of Refraction
The index of refraction (or refractive index) of an eyeglass lens material is a number that is a relative measure of how efficiently the material refracts (bends) light, which depends on how fast light travels through the material.
Specifically, the refractive index of a lens material is the ratio of the speed of light in a vacuum, divided by the speed of light in the lens material.
For example, the index of refraction of CR-39 plastic is 1.498, which mean light travels roughly 50 percent slower through CR-39 plastic than it does through a vacuum.
The higher the refractive index of a material, the slower light moves through it, which results in greater bending (refracting) of the light rays. So the higher the refractive index of a lens material, the less lens material is required to bend light to the same degree as a lens with a lower refractive index.
In other words, for a given eyeglass lens power, a lens made of a material with a high refractive index will be thinner than a lens made of a material with a lower refractive index.
The refractive index of current eyeglass lens materials ranges from 1.498 (CR-39 plastic) to 1.74 (a specific variety of high-index plastic). So for the same prescription power and lens design, a lens made of CR-39 plastic will be the thickest lens available, and a 1.74 high-index plastic lens will be the thinnest.
The Abbe value (or Abbe number) of a lens material is an objective measure of how widely the lens disperses different wavelengths of light as light passes through it. Lens materials with a low Abbe value have high dispersion, which can cause noticeable chromatic aberration — an optical error visible as coloured halos around objects, especially lights.
When present, chromatic aberration is most noticeable when looking through the periphery of eyeglass lenses. It is least noticeable when looking directly through the central optical zone of the lenses.
Abbe values of eyeglass lens materials range from a high of 59 (crown glass) to a low of 30 (polycarbonate). The lower the Abbe number, the more likely the lens material is to cause chromatic aberration.
Abbe number is named after the German physicist Ernst Abbe (1840-1905), who defined this useful measure of optical quality.
In addition to choosing a lens material that has a high index of refraction, another way to give your lenses a slimmer, more attractive profile is to choose an aspheric design.
Aspheric designs — where the lens curvature changes gradually from the center of the lens to its edge — enable lens manufacturers to use flatter curves when fabricating eyeglass lenses, without degrading the optical performance of the lenses.
Because aspheric lenses are flatter than conventional (spherical) lens designs, they cause less unwanted magnification of the wearer's eyes, for a better appearance. In some cases, aspheric designs also improve the clarity of the wearer's peripheral vision.
Most high index plastic lenses are made with aspheric designs to optimize both the appearance and the optical performance of the lenses. With polycarbonate and CR-39 lenses, an aspheric design usually is an option that increases the cost of the lenses.
Minimum Centre Thickness (Or Edge Thickness)
The FDA has guidelines for impact resistance, so there's a limit to how thin an optical laboratory can grind your lenses.
In (concave) lenses for the correction of myopia, the thinnest portion of the lens is the optical centre, located at or near the middle. In (convex) lenses that correct farsightedness, the thinnest portion of the lens is at its edges.
Because of their superior impact resistance, polycarbonate and Trivex lenses that correct myopia can be fabricated to a centre thickness of just 1.0 mm and still pass the FDA impact-resistance standard. Myopia-correcting lenses made of other materials usually have to be thicker in the centre to pass the standard.
The size and shape of your eyeglass frames also will affect the thickness of your lenses, especially if you have a strong prescription. Choosing a smaller, well-centred frame can significantly reduce the thickness and weight of your lenses, regardless of the lens material you choose.
Generally, the thinnest lenses for your prescription will be aspheric lenses made of a high-index material, worn in a small frame.
Advantages of High-Index Lenses
Thinner. Because of their ability to bend light more efficiently, high-index lenses for near-sightedness have thinner edges than lenses with the same prescription power that are made of conventional plastic material.
Lighter. Thinner edges require less lens material, which reduces the overall weight of the lenses. Lenses made of high-index plastic are lighter than the same lenses made in conventional plastic, so they're more comfortable to wear.
Lightweight lenses are even more of a benefit for farsighted prescriptions, which can make conventional lenses very heavy. And most high-index lenses also have an aspheric design, which gives them a slimmer, more attractive profile and reduces the magnified "bug-eye" look that conventional lenses cause in strong farsighted prescriptions.
Eyeglass Lens Treatments
For the most comfortable, durable and best-looking glasses, the following lens treatments should be considered essential:
If you're not going to wear sunglasses outdoors, make sure your eyeglass lenses block 100 percent of UV rays. Some lens materials don't without an added coating.
Anti-scratch coating. All lightweight eyeglass lens materials (see table) have surfaces that are significantly softer and more prone to scratches and abrasions than glass lenses. The softest eyeglass lens is also the one that is the most impact-resistant: polycarbonate. But all plastic and high-index plastic lenses require a factory-applied anti-scratch coating for adequate lens durability.
Most of today's modern anti-scratch coatings (also called scratch coats or hard coats) can make your eyeglass lenses nearly as scratch-resistant as glass. But if you're hard on your glasses or you're buying eyeglasses for your kids, ask about lenses that include a warranty against scratches for a specific period of time.
Anti-reflective coating. An anti-reflective (AR) coating makes all eyeglass lenses better. AR coatings eliminate reflections in lenses that reduce contrast and clarity, especially at night. They also make your lenses nearly invisible, so you can make better eye contact and you and others aren't distracted by reflections in your lenses. AR-coated lenses are also much less likely to have glare spots in photographs. Reflections can affect many surfaces such as water, glass, grass and metallic surfaces.
Prolonged exposure to reflection and sunlight can lead to visual fatigue and discomfort. Reflections can also contribute to an increased risk of accidents while driving due to slower reaction time.
Anti-reflective coating is especially important if you choose high-index lenses, because the higher the refractive index of a lens material, the more light the lenses reflect. In fact, high-index lenses can reflect up to 50 percent more light than CR-39 lenses, causing significantly more glare, unless AR coating is applied.
UV-blocking treatment. Cumulative exposure to the sun's harmful ultraviolet (UV) radiation over a person's lifetime has been associated with age-related eye problems including cataracts and macular degeneration. Thankfully all types of Jainam lenses protect eyes from such problems. Jainam lens provide 100% UV protection/UV 400 (both UVA and UVB) including blue light. Anti-reflective coating (also called "AR coating" or "anti-glare coating") improves vision, reduces eye strain and makes your eyeglasses look more attractive.
High Index Nano Pore Lenses- Jainam lens have characteristics most valued by consumers; clear vision, thinness, visual acuity, durability, scratch resistance and protection (UV and impact). We use Innovative Latest Nano pore technology to filter light. This makes us technologically advanced than our competitors.
The molecular structure consists of a hexagonal pattern of pores each roughly 200 nm deep and spaced on 300 nm centers. The structure is approximately the same as a quarter or a half a wavelength of light. This kind of pores allow the wavelength of visible light to pass, so the light sees the surface as having a continuous layer of high index between the air and the medium. The molecular structure is textured with 3D pyramids and 2D grooves (gratings). This nanostructured technology effectively eliminates high energy light & reflection, thus giving perfect performance. Natural low energy visible light passes through the lenses and reaches the eyes. Retinal cells are protected which helps in healing of damage caused by harmful rays occurs. Thus, eyes are most protected by Jainam lenses. This is a form of biomimicry. There is continuous research being done for improvement in technology mostly funded by Jainam.
Glass wasn’t strong enough. Polycarbonate wasn’t clear enough. Neither material allowed for adequate customization of tints and Light Transmission Levels. So, we set out to research for better lens material. Jainam lens material combines the superior optical quality of the finest glass and the lightweight, strength and impact resistance of polycarbonate. All of the best properties. No compromises. No short-cuts.
By using multiple layers of coating materials, it became possible to obtain minimum reflection at a single wavelength. Coatings that give very low reflectivity over a broad band of frequencies was possible to be made, although these lenses are complex and relatively expensive. Optical coatings are made with special characteristics, such as near-zero reflectance at multiple wavelengths and optimal performance at angles of incidence other than 0.
Depending on your lifestyle and how you will be using your eyewear, there are many beneficial coatings and add-ons that can significantly impact your wearing experience.
Anti-Scratch Coating - It is especially recommended for children. We offer a great coating called TD2 (write type of lens above 2000/-), which boasts a two-year warranty against scratches and lens damage. This is a great option for kids.
Anti-Reflective (Non-Glare) Coating - Anti-reflective (AR) coating eliminate reflections in lenses that reduce contrast and clarity, especially at night. (Ever notice those halos around street lights?) They also make your lenses nearly invisible, so you can make better eye contact without distracting reflections. AR coating is especially important if you choose high index lenses, because of the material more light is reflected causing more glare. We only utilize the best anti-reflective coatings offered, to make sure you're receiving a durable, easy to care for product.
Cost of Eyeglass Lenses and Eyeglasses
Depends on the type of lenses and lens treatments you choose.
So how much will your glasses cost?
The amount you pay for your next pair of glasses will depend on many factors, including your visual needs, your fashion desires etc.
Keep in mind that if you choose high-end designer frames and aspheric, high-index progressive lenses with premium anti-reflective coating, it's not unusual for the cost of your eyeglasses to exceed 5000.
On the other hand, if you're buying your child's first pair of prescription eyeglasses for mild myopia, the cost will be much closer to 2000 for quality eyewear, including a scratch-resistant warranty.
To get the best value, it's essential to understand the features and benefits of the products you are considering. But, does cost matter more than your eyes?
Maintaining healthy eyesight should be a priority no matter what age you are, or what activity you are doing. At Jainam we are committed to providing best in technology eye glasses with updated latest technology & research. Jainam lenses have coating on both sides of the lens for a clear view. Absorption of high energy rays starts from the surface of the lens itself, not limited by the reflection of the light that reaches the surface. Scratches and removal of coatings after years of wear & tear doesn’t affect the ability of lenses to filter high energy light. Hence even after years of wearing eye lenses, there is 100% absorption of UV light.