Would it be better to use a backside AR or front-side AR on XTRActive lenses?
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Would it be better to use a backside AR or front-side AR on XTRActive lenses?
Why not both?
My thoughts are: If we use a front-surface AR, then we would be increasing light transmission through the lens which would "decrease" the sunglass lens effect of the XTRActive. If we use a back-surface AR only, then the patient may not see as sharply because there is not an AR coating on the front. I suppose the main reason for not doing both the backside and front-surface is what I wrote in the first sentence. Is that a valid concern?Quote:
Originally Posted by Kwill212
I would do both sides and can't think of any reason not to.
I don't think it is a valid concern, I would and always do both front and back. Yes it increases light transmittance, but that comes with more utility for the patient that AR brings. One of the main reasons people get transitions is for the utility.Quote:
Originally Posted by Neophyte Optician
There is never a reason not to do back surface AR. Front surface is optional but usually preferable from an optical perspective. Cosmetically tinted lenses sometimes look better with no front surface AR.
AR on photochromics works well. Just do it on both sides. Unless it is a "blue blocking" coating, it will not negatively impact the properties of the photochromic.Quote:
Originally Posted by Neophyte Optician
Agreed, both sides, except as Robert_S said in case you favor the "plano sunglass" aesthetic of a reflective front surface.Quote:
Originally Posted by lensmanmd
Simply reasoning, I would think frontside AR would actually increase photochromic performance. Photochromics activate in proportion to light hitting the photo layer. Untreated lens surfaces reflect away 5% or more incoming light, preventing it from hitting the photo layer. AR will increase transmittance through the front surface delivering more light to the photo layer, which will activate more and block that additional light. The lens will darken more and the wearer will receive no additional light. Win win?
I had a physics professor prove to me that antireflective coatings do not allow more light pass through a lens. I will admit I really didn't fully grasp the math he used but the concept stayed with me. He said the marketing material claiming 99.9% light transmission was false. He said the coatings used constructive interference to “cancel” out the reflections at the surface.Quote:
Originally Posted by Neophyte Optician
I wear Trans XTRActive and Sensity Dark with AR front and back. Also Drivewear with AR front and back. Love it all. My eyes are quite spoiled. Coat those lenses front and back!
That's really interesting. But, it can't be true, or there wouldn't be an advantage to ARC on camera lenses, or microscope lenses etc... because if AR didn't increase light transmission, it would be redundant. It certainly isn't there for cosmetics... Or is the purpose simply to reduce ghosting?Quote:
Originally Posted by Excel-Lentes
Well, the best way to settle this is to have a fixed, lab quality full spectrum light source, measure it with a calibrated visible light photometer of appropriate sensitivity at a fixed distance, and then again at the distance that represents the given thickness of the lenses being tested. Use a plano lens of a resin that is pure with well documented, consistent properties at the predetermined thickness at the premeasured fixed point. Then measure using the photometer directly behind the lens once it is at the appropriate fixed position. Repeat for at least 2 more lenses from the same batch. Afterwards, put frontside AR on one, backside AR on one, and front and backside AR on the last one. Repeat the above procedure for those 2 lenses. Compare results.
This isn't a perfect setup, but it should show any significant differences easily.
Or we can just trust this page:
http://hyperphysics.phy-astr.gsu.edu...t/antiref.html
Interestingly, if the index of the coating is lower than the index of the lens, you increase transmittance. If the index of the coating is higher than the index of the lens, you decrease the transmittance. So, it's not a simple case of just increase or decrease, it is dependent on the index of the coating, or if a stack, then the indexes of the coatings. Also, according to this page, the optimal index for a single coating is the square root of the index of the material being coated. I had no idea it was that simple. The calculation for a stack seems nastier the more complex it is.
It's probably a guarantee that the stacks used today are all optimized to increase transmittance, as they say.
Remember Transitions is activated by UV not visible light. Most materials block uv except cr and many AR coating are formulated to do the same. So the goal is to not block uv.
With regard to XTRActive, you are incorrect. XTRActive is activated by both UV and visible light, as per this PDF from transitions.com:Quote:
Originally Posted by Lensman11
https://trade.transitions.com/resour...eetandFAQs.pdf
They indeed react to visible light but not the the full spectrum. They do not activate to their full potential in a car because the uv is blocked. If they reacted to the full spectrum they would not lighten indoors during the day.
Your physics professor is partially correct. Let's say that in a perfect environment, physics will hold true regarding the throughput of light in controlled environments. However, the physics does not take into account the reflection that is inherent to each index of refraction in real world environments.Quote:
Originally Posted by Excel-Lentes
There is not enough room here to dissect this, nor do I have enough time for a dissertation. Take it for what it is.
Destructive interference, which is what AR coatings are designed to do, reduces unwanted reflection, both externally and internally, providing truer light transmission through the material. Energy reflected is energy wasted. The added transmission may be a negligible 2%, or a more significant 10+%, based on the material.
Destructive interference. Where does the cancelled energy go? Through the lens, increasing light transmission, satisfying the conservation of energy law.Quote:
Originally Posted by Excel-Lentes
https://www.tf.uni-kiel.de/matwis/am...ed/t5_1_3.html
Best regards,
Robert Martellaro
Robert and lensman are right above. At least that's what I always thought I knew.
these are the measured transmissions of a CR39 lens and the same lens with an AR on both faces.
The transmission increases and a lot
Shimtzu UV2600 spectrophotometer instrument with integrating sphere
sorry for the different wavelength scales
https://www.optiboard.com/forums/ima...BJRU5ErkJggg==
I would say that is the proof in the pudding.