Anti-Reflective treatmen: A luxary or necesity

Lenses / Tecnology

When light falls upon an optical medium, one part of it is refracted, another one is absorbed by the lens’ material, and the rest is reflected. Untreated lenses only let 92% pass through them, while the other 8% is reflected on the lens, reducing its transparency and the quality of sight. The anti-reflective treatment looks to eliminate these reflections and better the light’s transmission.

Why is Anti-Reflective Treatment so Interesting?

Every optical surface produce these reflections, which means that when light falls upon the surface of the lens, they produce annoying glares, sheens and a loss of contrast.

With anti-reflective treatment, we manage to improve in many aspects, such as in comfort, better vision, reducing glares from vehicle lights and better esthetics.

It can be hard to believe, but anti-reflective treatments offer these benefits as a complement to any lens. The same technology used to on precision lenses in microscopes and cameras are now available for improving the health of your eyes.

The anti-reflective treatment applied on the front and back of the prescription lens greatly reduces the light reflected on its Surface. As a result, the eyes see clearer, the vision is more defined, and the glares of reflected objects, like vehicle lights are almost completely eliminated. Also, if your glasses have a lot of magnification, this treatment makes your eyes look more natural.

 How does the Treatment Work?

Anti-reflective treatments consist of a covering of multiple thin layers of metallic oxides that are applied to both sides of the lenses in order to eliminate reflections and reduce glares. Since it facilitates the light’s transmission, it improves the contrast and filters the UV rays. This treatment reduces the effects of macular degeneration, cataracts, and other age related disorders.

The anti-reflective treatment can be done on lenses of any material in the market as a step before assembling the lens on the frame.

At the same time, other than reducing glares, it also reduces ghost images and distortions caused often by high formula lenses, which helps the patient adapt to these types of lenses

The use of AR is recommended for all activities, but particularly so for those who work with fluorescent lights or with computers, and to help with night time driving.

Application

The anti-reflective process is done in the optic laboratory with specialized machinery.

The surroundings must be clean, with no dust and a good flow of air. After cleaning the lens, it is left in a vaccum chamber where the anti-relfective layers are applied on the front and back surfaces.

Advantages

The clinical and technical advantages of the treatment are so important and recognized, that various European countries have their application as obligatory for driving and piloting.

Its use is important during shooting practice, fishing, skiing, using a computer, and indoors with artificial light.

They also offer clear clinical and esthetical advantages for their users, allowing them to see easier with colored lenses, whre the transmission of light is significantly reduced.

But as well as their technical qualities, the treatment offers a series of important esthetic advantages, since by being practically invisible, it allows for the wearer’s eyes to be seen more with less reflections, giving them a more natural look.

 How are the Reflections Produced?

The purpose of the layering of the lenses is to reduce the reflections on the surface of the lenses. The light is reflected due tto the lenses surface having a different refraction index than air, and the reflectioncan occur in this area at different refraction indexes. Anyone can see their image reflected from glass.

Light acts like a wave: when light falls upon the surface of the lens, some of it bounces off it as a reflection. The reflected ray has the same characteristics of the starting ray’s waves, it just moves in the opposite direction.

Interference

Since the reflection is made up of waves, it has an important characteristic: it can be nullified by another wave, as long as this other wave is exactly the same as the other, but in a opposite phase. This is called Destructive Interference.

We can make this happen by doing the following: if we simply place a second reflection (the anti-reflective treatment) spaced on the lens ¼ the longitude of the light’s wave, when both reflections meet, they’ll interfere with each other.

 How it works

When someone uses glasses without this treatment, they will see the reflections of this light coming from the front and back of the lens. This light is reflected from the back surface, and bounces between the front and back surfaces before exiting. These reflections mime the image of the observer. Ghost images are frecuent with glasses, especially while driving at night. They’re images created from the reflections that come from the internal surface of the lens.

. The reflections that come from the posterior face of the lens are also annoying, but it is more noticeable in sunglasses because the tint acts like a mirror.

Back to front reflections are also most noticeable with spherical glasses because their interior flat face reflects more light.

Lenses with high negative power can cause a “bottle effect”, because the light is reflected from the edges, which are thicker. They appear like a series of concentric reflections (rings)

All of these reflections are virtually eliminated with an anti-reflective coating.

In order to reduce the number of reflections on the optical surfaces, the treatment, as said, consists in applying thin layers of different materials over the lenses. In the intervails air/layer-layer/lens, mutual cancelation of the reflected fractions of light is produced, according to the Interference Principle. In order to achive this effect, you’ll need at least three layers (which when applied to both sides they become six), which must be combined in accordance to the refraction index and the thickness

The treated lenses receive a residual color that basically depends on the decision made by the company that does the AR and is a characteristic color, regardless of the lens’ material. This detail is very useful for the user: the specialist can easily identify which anti-reflective treatment it is and offer the standard when the lens’s material changes.

 Benefits of Anti-reflective Treatments

 As the name suggests, this treatment’s purpouse is to eliminate as many undesired reflections on the lenses as possible (up to 99.5%), which lowers visual effort and allows for more light entry into the eye, leading to better vision.
Among other benefits, anti-reflective treatment gives us clearer images due to more transparancey; it increases visual acuity, as well as our spatial and stereoscopic senses. The treatment produces better vision quality because of a significant reduction in the percentage of light that reflects off the surface of the lens, which transforms into an increased percentage of transmited light energy. This means that under determined light conditions in your surroundings, the feeling that users get while using glasses with this treatment is that of “brighter images”.

 Anti-reflective Associated Treatments

When you buy multi-layered, anti-reflective treated lenses, as a general rule they come with additional improvements as “extra treatments”, called “Clean Glasses”

ï          Antistatic treatment: Very useful for PC users. When cleaning your glasses or being in front of a CPU, a static electric charge is created on the surface and it attracts dust particles. The antistatic treatment significantly reduces this effect while also blocking the passage of these waves through the lens.

ï          Hydrophobic Treatment: Repels water, meaning that the drops of rain wont easily stick to the surface of the lens (they don’t disappear completely, but the become smaller)

ï          Oil Repellent: Generally associated with the hydrophobic treatment because by reducing the ease with which fluids can adhere to the lens, the chances of getting dirty become lower.

ï          Scratch Resistance: Helps your lenses get scratched less with daily use, but it doesn’t prevent scratches from porr handling or cleaning with inadequate products

ï          UV Filter: Offers protection against harmful ultraviolet rays with an E-SPF between 2 and 5

 Why are the Prices of Lenses with an Anti-Reflective Treatment Higher?

The price difference is completely justified because the technology needed to add the AR treatment, plus all the extra treatments, is extremely expensive and complex, but the increase is nothing in comparison with the received visual benefits.

The way you clean AR treated lenses is very important, especially sense these are coatings. As with any lens, you must be careful if you want to protect them. You must avoid dry cleaning them and not use any sort of tissue or fabric if you want to keep them scratch free. You can use water, a mild soap and high quality facial paper. There is an aerosol cleaner specifically for AR treated lenses which greatly facilitates the cleaning process.

Credits:  publish by Jose Andres Vasquez Prieto

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