How can you tell if lenses have an anti-reflective coating?
Anti-reflective lenses can be recognized by the residual reflection. Regardless of the material used for the lenses, they have a characteristic colour when you hold the glasses at a slight angle against a white background. This is highly practical for the wearer: the optician can identify the anti-reflective coating and even offer the same high quality if a switch to another material is desired.
The residual reflection is usually green. The modern DuraVision® Premium lens coating from ZEISS has an attractive, bluish residual reflection. The barely perceptible bluish residual reflection increases the amount of light the lens transmits to your eyes. And not only that &#; the blue is less visible to the eye. This means lenses with this residual reflection have the advantage of making your eyes look clearer to other people and have fewer reflections. Your eyes look more natural, almost as if you&#;re not wearing glasses at all.
So why not talk to your optician about the anti-reflective coating services on offer and about the coatings&#; durability today! Ask for their tips about what you need to look out for to ensure your coating lasts as long as it ought to.
Traditionally, lenses and optical components were coated in soft coating. This is a process that might become obsolete because of the development of a high performing technique known as hard coating. This coating provides myriad advantages over traditional soft coatings.
As background, soft coatings are multiple layer films that are used over optical components. The film usually consist of silver, zinc sulfide or cryolyte. In a traditional setting the layers are stacked vertically upon the optical lens and offer protection from environmental contaminants. A soft coating is fragile and the edges of the coating material can degrade if it&#;s exposed to moisture and through typical use.
The use of hard coating on lenses and optical components offer increased benefits compared to their soft counterparts. To add this hard film it is applied in a controlled atmosphere using computer generated programs. The reason for this type of application is that it assures the coating is applied evenly and that it is beneficial for use in high stress environmental settings. Not only is the hard coating believed to be more consistent than soft coatings, but it provides a higher level of wavelength absorption. A hard coated lens is superior in the transmission of wavelengths as compared to soft coating by a margin of up to 90% more.
Hard coatings remain constant in their transmission while soft coated lenses and optical components gradually change over time and through use.
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A lens is incomplete without the appropriate coating on its surface. In this article we will discuss two types of spectacle lens coatings available and their benefits.
Coating is a feature of the lens that can increase wearer&#;s satisfaction, enhance optical properties and improve cosmetic attributes of the lens.
In the last one-decade Ophthalmic lens coatings have evolved in several dimensions resulting in better and better transmission thereby making lenses more invisible. Research also advances in offering protection with the help of these coatings and added a wide range of product options in the scope of Blue Light Protection and much needed UV protection.
Let&#;s discuss Scratch resistant coating and ARC coating in the article below:
Scratch-Resistant Coatings (SRCs)
Because of the tendency of plastic lenses to scratch more easily than glass lenses, manufacturers have developed processes of coating the plastic lens to develop more surface hardness and thus more resistance to scratching.
SRC lenses are not specifically designed to reduce lens reflections. SRC plastic lenses, however, do exhibit some reduction of lens reflections. This means that they will have a higher light transmission compared with a non- SRC lens or an Uncoated lens.
Scratch-resistant coatings are also called anti-scratch coatings or hard coatings. In trade you may find this coating with several names such as Titus, Titanium or simply Hard Coat.
But then this was not enough. An uncoated CR-39 plastic lens transmits about 92% of the incident light. By adding an Scratch Resistant Coating to the lens, transmission may increase to just short of 96% but that still annoys the wearer and also makes eye contact difficult.
Especially in the age of selfie who would want to have hidden eyes by the flashlight. So Hard Coat, as Scratch Resistant Coatings are also referred to, is good to make lenses durable and scratch resistant but Anti Reflection Coating is an essential option to offer your customers today.
Anti Reflection Coatings
An AR coating is a thin, clear layer or layers applied to the surface of a lens. Its purpose is to:
(1) reduce unwanted reflections from the lens surface and
(2) increase the amount of light that passes through the lens to the eye.
Let us now first understand the cause of reflections
Spectacle lenses are manufactured using lens material, as raw material we use plastic (CR-39 or Polycarbonate) or mineral glass (not so common nowadays) as lens material.
Each lens material has got few inherent properties like refractive index, impact resistance, abbe value and density and lens behaviour wherein when light passes through the lens some get lost or reflected and rest of transmitted. This reflected light causes annoyance and it happens on both the front and back surface.
Most of the available lens materials can transmit up to 92% of light whereas the remaining 8% gets reflected. This reflection is 50% higher in High index lens material.
Which means High index material can reflect upto 12% and may go upto 14.1% thereby reducing transmission by another 4% &#; 6%, leaving 85.9% transmitted.
A good ARC can improve transmission upto 98% to 99% and modern-day ARC coating is developed with much higher strength and it doesn&#;t get scratched easily.
The Theory of Antireflection Coatings : A Brief Introduction
According to optical theory, for a single-layer AR coating to reduce reflections, an AR coating must meet two conditions: the path condition and the amplitude condition.
The Path Condition: Very simply stated, the path condition determines what the optical thickness of a single-layer coating film must be. To achieve the desired effect, the film must be either one fourth of a wavelength (i.e., one fourth, three fourths, five fourths, and so forth).
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As light strikes the single layer&#;coated lens surface, some of the light will reflect from the coating surface and some from the lens surface. This causes the two reflected waves of light to be out of phase with each other, causing destructive interference and preventing reflection.
The Amplitude Condition: The amplitude condition requires that the amplitude of the light waves in the lens material and in the film be equal. This is required so that the destructive interference of the two reflected waves will be complete, where the two sine waves combine to form the zeroed-out straight line.
The distance from the top to the bottom of the wave must be the same. This can be achieved by controlling the index of refraction of the film.
But Single-Layer Anti Reflection Coatings are not 100% effective and hence what you see and dispense is always multi-layer ARC.
Multi &#; layer ARC and arrangements of its layer also results in another attribute of the coating and referred to as color of the coating. Green HMC or Blue ARC are such examples.
But the options in ARC coating are evolving day by day and that has made ARC, a subject much deeper to study and critical while accessing which one is the right option for your consumers.
In the next article we will cover types of ARC and selection criteria based on consumer profile.
Lens coatings are applied to eyeglass lenses to enhance the durability, performance and appearance of your glasses. This is true whether you wear single vision, bifocal or progressive lenses.
If you&#;re thinking about purchasing new eyeglasses, you might want to consider the following lens coatings and treatments.
Anti-reflective coating (also called AR coating or anti-glare coating) is a microscopically thin multi-layer coating that eliminates reflections from the front and back surface of eyeglass lenses.
By doing so, AR coating makes your lenses nearly invisible so people can focus on your eyes, not distracting reflections from your eyeglasses.
Anti-reflective coating also eliminates glare caused by light reflecting from your lenses. With reflections eliminated, lenses with AR coating provide better vision for night driving and more comfortable vision for reading and computer use.
AR coating is highly recommended for all eyeglass lenses, but particularly for polycarbonate and high-index lenses, which reflect more light than regular glass or plastic lenses if anti-reflective coating is not applied.
Also, aspheric lenses, which have flatter curves than regular lenses, often cause more noticeable reflections, so AR coating is highly recommended for these lenses, too. And AR coating is beneficial when applied to the back surface of sunglasses to eliminate "bounce-back" reflections when you are facing away from the sun.
For the best possible comfort in all lighting conditions, eye care professionals usually recommend applying anti-reflective coating to photochromic lenses. AR coating improves light transmission through the lenses for night driving and helps photochromic lenses reduce glare in bright sunlight.
No eyeglass lenses &#; not even glass lenses &#; are 100% scratch-proof.
However, lenses that are treated front and back with a clear, scratch-resistant coating have a much harder surface that is more resistant to scratching, whether from dropping your glasses on the floor or occasionally cleaning them with a paper towel.
Kids&#; lenses, especially, benefit from a scratch-resistant hard coat for greater durability.
Today, most eyeglass lenses, including high-index lenses and lenses made of polycarbonate and Trivex, have a built-in scratch-resistant coating.
Since scratch-resistant coatings are sometimes optional, make sure your optician knows that you want your eyeglass lenses to include hard coating for extra durability. Also, ask about the warranty on eyeglass lenses that are treated with scratch-resistant coating versus those without the coating.
Keep in mind that even the best scratch-resistant coating can&#;t completely protect your lenses from wear and tear. To keep your glasses looking new, store them in a cushioned case when not in use, and clean your lenses with a microfiber cloth and the cleaning solution your optician recommends.
Also, be wary of products that promise to repair scratched lenses. These products may fill in the scratches, but it is impossible for them to make the scratches disappear so the lenses look new again.
If you live in a cold climate, nothing is more frustrating than having your eyeglasses fog up when you come in from the cold. This also can be a safety issue, since it limits your ability to see until the fog clears. Lens fogging can be especially dangerous for police officers and other first responders to emergency situations.
At least one eyeglass lens coating company (Opticote) has created a permanent coating designed to eliminate this problem. The factory-applied coating &#; called Fog Free &#; eliminates the condensation of moisture on lenses that causes fogging.
So your lenses and vision stay clear when you make the transition from a cold environment to a warm one. It may also keep your lenses from fogging up during sports and other times you are hot and perspiring.
Fog Free can be applied to plastic, polycarbonate and other eyeglass lenses, including high-index lenses and Transitions photochromic lenses. The anti-fog coating is applied to the lenses before they are cut to fit into your frame at the optical lab. Ask your optical retailer about pricing and availability.
Another option in anti-fog lens technology is Optifog lenses.
The anti-fogging property of Optifog lenses is activated by applying a drop of Optifog Activator to each side of the lens, then wiping the lens with a microfiber cloth to thoroughly spread the liquid across the entire lens surface. This treatment keeps the lenses fog-free for up to one week.
Lens fogging is caused by tiny water droplets that form by condensation on the surface of eyeglass lenses when the lenses are significantly cooler than the surrounding air temperature. Optifog works by uniformly spreading these water droplets across the lens surface so they become invisible.
Optifog lenses are available in plastic, polycarbonate and high-index plastic lens materials, with or without EssilorLuxottica&#;s proprietary Crizal anti-reflective coating.
Another beneficial lens treatment is an invisible dye that blocks ultraviolet (UV) light. Just as sunscreen keeps the sun&#;s UV rays from harming your skin, UV-protective treatments for eyeglass lenses block those same rays from damaging your eyes.
Overexposure to ultraviolet light is thought to be a cause of cataracts, retinal damage and other eye problems.
Regular plastic eyeglass lenses block most UV light, but adding a UV-blocking dye boosts UV protection to 100% for added safety. Other eyeglass lens materials, including polycarbonate and most high-index plastics, have 100% UV protection built-in, so an extra lens treatment is not required for these lenses.
Photochromic lenses also block 100% of the sun&#;s UV rays without the need for an added UV lens treatment.
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