Why is AR green ?

[skirk1975]

Why is AR green-ish. I know there is an answer for this. I just forget. And with that in mind, how is Zeiss able to Gold ET or Revolution able to do "color free"? There is something about greens position on the color scale and it is at ist's best performance there? Someone break it down for me.......

Thank You.

[Darryl Meister]

Each high-index layer of an anti-reflective coating can only completely eliminate reflectance for a single wavelength (color) of light. Other wavelengths are partially reflected, resulting in residual reflections from other colors of the spectrum that remain visible. These reflected colors form the "reflex color" of the coating.

Early AR coatings utilized a single layer of magnesium fluoride, which eliminated light completely for wavelengths near the middle of the visible spectrum. Red and blue light from the two ends of the spectrum were still reflected, however, resulting in a conspicuous purple reflex color.

Additional wavelengths of light can be completely eliminated using more than one high-index layer. Modern AR coatings use several high-index layers, producing a multi-layer or broadband AR coating that eliminates reflections over a broad range of wavelengths. These coatings often have peak reflectance in either the middle (green) or blue ends of the visible spectrum.

By controlling the thickness and number of coating layers, the residual reflections can be attenuated for different wavelengths. This allows thin film engineers to control the intensity and hue of the reflex color of the AR coating.

[Jacqui]

Thank you Darryl That tells me why the old AO (1960's) AR was pink. it was a lovely pink, almost like a light Cruxite.

[FVCCHRIS]

Those purple lenses. A/R has definitely come a long way. Yes, I said that. There are several good coatings available today that you can use to vary the reflex color. Green, blue, even gold if the patient feels it will be a more desirable finished product. Shop around and get samples of each you feel you might want to offer your patients.

[spexwala]

Now this customer of mine wants the flash from a camera,to not show at all in the picture.Does any AR coating guarantee that?
The rx being About -4.50/-1.25X90 BE
regards
Vimal

[cocoisland58]

The camera flash will not show up on an AR coated lens in my own experience.

Sold the Gold AR a few times years ago and yuck. The less color the better I think. My Alize (or is it Avance?) has very little.

[Fezz]

"Why is AR green?"

Simple!

They are green like the money and profit generated!*






*That is if you CONvince a patient that spending almost as much on the AR coating than they did on the lenses is a wise investment of their hard earned GREEN!

[finefocus]

Those purple lenses. A/R has definitely come a long way. Yes, I said that. There are several good coatings available today that you can use to vary the reflex color. Green, blue, even gold if the patient feels it will be a more desirable finished product. Shop around and get samples of each you feel you might want to offer your patients.

Remember, this is the reflex color, not a tint color. An A/R with green reflex doesn't absorb like a green-tinted lens. Green, blue or otherwise, the patient sees the same.

[finefocus]

"Why is AR green?"

Simple!

They are green like the money and profit generated!*






*That is if you CONvince a patient that spending almost as much on the AR coating than they did on the lenses is a wise investment of their hard earned GREEN!

Are you still riding that old horse? Are you calling me a "con" artist, a thief? You shouldn't.

[Darryl Meister]

Remember, this is the reflex color, not a tint color. An A/R with green reflex doesn't absorb like a green-tinted lens. Green, blue or otherwise, the patient sees the same

Keep in mind that transmittance for any wavelength (color) is reduced by reflectance. Assuming that absorption and scatter are negligible, the total transmittance T is given by T = 100% - R, where R is the percent reflectance.

So, a lens that reflects more green light will have more transmittance in the blue and red ends of the spectrum, whereas a lens that reflects more blue light will have more transmittance in the green and red bands. Consequently, since the sensitivity of the eye varies with wavelength or color, the choice of reflex color can influence the luminous transmittance of the lens, as perceived by the eye.

That said, the differences are small enough not to influence the patient's perception of color.

[sharpstick777]

Darryl,
I never thought I would live to find fault with any of your answers, but I will have to disagree in part. The question was not why A/R's have color per se, but why manufactures choose "Green" for their A/R color I think.

Answer:

Green A/R has a higher yield, due to less color variation between batches, which means that manufacturers have to throw away fewer lenses because they don't match colors. Slight variations in Green A/R show up less noticably than other colors. Although A/R can be made in other colors than green, color variations are more likely and/or more noticable in other colors, resulting in more lenses that don't pass inspection, and higher manufacturing costs.

By controlling the thickness and number of coating layers, the residual reflections can be attenuated for different wavelengths. This allows thin film engineers to control the intensity and hue of the reflex color of the AR coating.

[Darryl Meister]

I never thought I would live to find fault with any of your answers, but I will have to disagree in part. The question was not why A/R's have color per se, but why manufactures choose "Green" for their A/R color I think.

I don't necessarily disagree with your response regarding yields. My own answer was simply to explain that, with modern multi-layer AR coatings at least, thin film engineers can obtain a wide variety of hues by altering the AR stack appropriately, are are not restricted to green or any other color.

We choose blue instead of green for some of our own anti-reflection coatings, for instance, because it produces a lower luminous reflectance and higher luminous transmittance, thereby resulting in a clearer lens.

[finefocus]

I don't necessarily disagree with your response regarding yields. My own answer was simply to explain that, with modern multi-layer AR coatings at least, thin film engineers can obtain a wide variety of hues by altering the AR stack appropriately, are are not restricted to green or any other color.

We choose blue instead of green for some of our own anti-reflection coatings, for instance, because it produces a lower luminous reflectance and higher luminous transmittance, thereby resulting in a clearer lens.

Darryl, could you please elaborate. Clearer to look through, or clearer to look at? Any difference in optical performance?

[For-Life]

I find the blue are clearer to look at and look through.

I know Crizal offers the Crizal D here. It is reported that the Green Crizal (regular Crizal) has 99.2% light transmission and the Blue Crizal (Crizal D) has 99.6%. Now, whether those numbers are accurate or not, there is a difference. Now the question is if that difference is noticeable, and I would say definitely. When I first started using Crizal D, a couple of times when the glasses were first dispensed the optician thought for a second that we forget to insert the lenses into the frames. I also notice less ghost when looking through them.

Interesting enough, Trio, which is a cheaper Essilor coating, advertises that it has 98.8% light transmission, and is one pretty ugly coating. So it shows how much an effect 0.4% has.

[Uilleann]

There's a lot more that must be going on here than is showing on the surface I believe.

I personally challenge ANY human eyeball to discern the difference in 0.4% light transmittance between two lenses. I'll eat this donut right here if anyone can prove to me in a scientifically controlled independent test that is then repeatable on a large segment of the general spectacle lens wearing population.

And I'm telling you - I do *NOT* like the jelly filled ones.

Bri~

[For-Life]

There's a lot more that must be going on here than is showing on the surface I believe.

I personally challenge ANY human eyeball to discern the difference in 0.4% light transmittance between two lenses. I'll eat this donut right here if anyone can prove to me in a scientifically controlled independent test that is then repeatable on a large segment of the general spectacle lens wearing population.

And I'm telling you - I do *NOT* like the jelly filled ones.

Bri~

I found that instead of finding four spots on my lenses where I see reflections, I noticed two. It is also much softer.

I do not have a scientific study, but I think you should eat your jelly filled donut.

And this is not about liking one brand over the other. I can chosoe Blue or Green Crizal. I can choose Blue or Green or Gold Zeiss. I can choose blue from Teflon or green from Super Hi.

It is the fact that I notice a better lens in the blue, whoever supplies it.

[FVCCHRIS]

When selling A/R coat- once you get past the cost, I always point out the reflex color to the patient so there are no "surprises" at dispensing. On the few occasions I detect that I'm working with someone who may feel that "green color" is raining on their fashion parade, that's when I will offer the alternative colors of blue or gold as a possible alternative.

[Uilleann]

I found that instead of finding four spots on my lenses where I see reflections, I noticed two. It is also much softer.

I do not have a scientific study, but I think you should eat your jelly filled donut.

And this is not about liking one brand over the other. I can chosoe Blue or Green Crizal. I can choose Blue or Green or Gold Zeiss. I can choose blue from Teflon or green from Super Hi.

It is the fact that I notice a better lens in the blue, whoever supplies it.

Crizal actually does not offer a lens with a blue reflex color.

But what you're stating isn't the light transmittance, rather your perceived impression of the given reflex color of a given A/R lens. That is a completely different and separate function when compared against light transmittance as you made mention of earlier, just to be clear.

Many of the "color free" A/R offerings will tend to lean more towards a blue reflex than green, though I have seen two manufacturers who tended more towards the old gold cast. Regardless, there are certain lenses that will exhibit a much more noticeable reflex than others - and that does not take a trained eye to discern.

All the best!



Bri~

[Darryl Meister]

I personally challenge ANY human eyeball to discern the difference in 0.4% light transmittance between two lenses.

Here are two photos comparing the reflectance of PureCoat by ZEISS (blue) and a standard AR coating (green), taken side by side. The standard AR reflex color is noticeably brighter than the PureCoat reflex color.

Regardless of whether a particular individual can discern a difference of 0.4% in transmittance, many eye care professionals choose to offer their patients the best vision possible. This goes for premium AR coatings, free-form lenses, or even taking a few extra minutes in the exam lane to nail down the perfect refraction...

[For-Life]

Crizal actually does not offer a lens with a blue reflex color.

But what you're stating isn't the light transmittance, rather your perceived impression of the given reflex color of a given A/R lens. That is a completely different and separate function when compared against light transmittance as you made mention of earlier, just to be clear.

Many of the "color free" A/R offerings will tend to lean more towards a blue reflex than green, though I have seen two manufacturers who tended more towards the old gold cast. Regardless, there are certain lenses that will exhibit a much more noticeable reflex than others - and that does not take a trained eye to discern.

All the best!



Bri~

The Crizal D is offered in Canada.

[braheem24]

what you're stating isn't the light transmittance, rather your perceived impression of the given reflex color of a given A/R lens. That is a completely different and separate function when compared against light transmittance as you made mention of earlier, just to be clear.

It's not when you're looking in a mirror at yourself.

Bicep curl, open mouth, stick in donut!

[Uilleann]

Nice photo. That green/yellow "standard" A/R lens is made by who exactly? None of the A/R lenses we use with any hint of a green cast look like that so I'm curious. We did once have a lab with a 'house" variety that left a very noticeable reflex...needless to say we didn't use it long.

However, it seems you're still confusing reflex color with light transmittance though folks. The color you see in the mirror or anyplace else is the reflex - and does not denote anything other than the color chosen by the optical engineers when they designed their particular stack formulary. Broad band transmittance is not the same as reflex color. The 0.4% transmittance figures quoted earlier in the thread between "brand A" and "brand B" still remain to be proven.

So I retain my waistline.

[For-Life]

I am assuming that the change in colour from Essilor Trio to Essilor Crizal to Essilor Crizal D were the reasons for the increases in light transmissions

[Uilleann]

Is the "Trio" Canadian too?

Because down stateside, it's the "Trion" A/R lenses used in the Essilor Jr. Package. Completely different product? Must be? Our's ain't blue here either - blue/green perhaps, but more green than blue. The Crizal family has much less residual color all around.

[skirk1975]

Wait a minute. With this all in mind, assuming that it is largely a matter of "yield" and manufacturing costs, than why can't I get a RED AR ? I have never seen one of those.