Anyone know how much the AR will actually increase the light transmission on sunglasses? It's obviously not going to negate a tint or mirror. It may actually reduce back reflection from the front side.Originally Posted by sharon m./ aboc
Anyone know how much the AR will actually increase the light transmission on sunglasses? It's obviously not going to negate a tint or mirror. It may actually reduce back reflection from the front side.
Depending on lens material light transmission may increase by 2% to 4%.
2% to 4% less light would also be back reflected from the front?
Backside AR is not to increase light transmission but to stop reflected glare from a source behind the wearer from reflecting into the eye and obviateing the images in front of the wearer.
Chip
We were discussing the plus and minus of front side AR on sunglasses though. Increase transmission thus defeating the fact that it is a sunglass somewhat or does it actually reduce any back reflected light from the front side surface due to this increase in transmission.
There is no advantage to front side AR on a sunlens that you intend use to block light. I thought I was clear on this point. dochsml, you seem to try to make a reason to use this front AR. If you want front AR and can order it I suggest you do.
Not trying to make a case. Just want to discuss all the ins and outs. You seem to be the only one making a case against it. It seems that this is the standard in the industry yet is debated in my circle. As you can see from my # of posts, I am new to this board and would like to hear the opinions (preferrably fact based) of people in the business whom I would otherwise never hear from. I've actually decided to go with a front side flash mirror and backside AR but would still like to hear from people on the subject. Sorry if I irritated you with my beating of a dead horse on this, that wasn't my intention. I really appreciate all the facts you have contributed to this thread. I wouldn't go as far as to say that there are NO reasons not to use front side AR though. Following the thread, there is the possibility of a surcharge for backside only, no hydro on the front, and the possibilty of reducing reflection. In fact, ACE seems to take the exact opposite viewpoint of you. That being said, your point of purposely increasing the transmission of a lens that is supposed to do the opposite is well taken. If you can't tell, this is more than just a casual interest of mine. My background is with PVD thin films only some of which include visual AR but I don't pretend to know it all. Like I said before, I've already made my decision but am still hungry for information and everyones' input in a real life application.
dochsml: Since you know thin film principals I can explain it this way. Why for almost no benefit attempt AR on the front? The other fact to consider is that due to the fact that cost of production is a factor most producers of AR and mirrors keep known repeatable processes as there standard.
I constantly get requests for a mirror color that is not currently offered. When we tell them the development costs of a new mirror including testing, all have changed their mind. Many custom options are possible it is just how much do you want to pay.
I see know potential benefit. We have actually tested SiO2 on the front surface for hydrophobic bonding to see if there was any additional bonding compared to the Silicon in the hard coating. So your thought process has been explored by me personally. Hard coating, AR thickness etc. are all important componates of a complete quality lens.
As well as front-side AR having very little use on a sunglass lens, I find in certain light the residual colour from the AR becomes more obvious and alters the over-all look of the sunglass. It can alter it to the point of the client thinking their is a coloured mirror on the front surface.
Also, clients tend to hate the front side AR, because it makes their eyes more visable through the tint
Not to mention that front-side AR scratches a lot easier that a lens without same. People tend to get thier sunglasses in situations that are more likely to create scratches.
Chip
It is my understanding that at best we are talking about less than 2% and I’ll let others who know more about this process explain. Most important I would think is that AR coating allows light to enter the eye at a usable angle. Glare from the front surface of a lens doesn’t just bounce away without an undesired affect. For that last 2% we can let the iris do it's job.
That's a very valid point. More consumables to apply the front side AR, more cost to the lab. And I know what you mean about the mirrors. Not to mention the people that want double gradients which require special tooling. I just got a bad taste in my mouth by a lab wanting to charge me more for backside only because they mostly do both side AR and would have to "separate" it out. This raised my eyebrow since I figured they would just stop processing it after the back side hence less consumables. And I certainly didn't want to pay any more to not get front side hydro. I thought about getting both side AR to get something that I wanted (front side hydro) and pay less than backside only. That is why I decided on the flash mirror.(costs the same as both side AR *shrug*). I would be curious to see your test results on the hyrdro to hard coat (i assume that is also with no ion gun treatment), but I'm not going to ask. Thanks for your input.AWTECH:
dochsml: Since you know thin film principals I can explain it this way. Why for almost no benefit attempt AR on the front? The other fact to consider is that due to the fact that cost of production is a factor most producers of AR and mirrors keep known repeatable processes as there standard.
I constantly get requests for a mirror color that is not currently offered. When we tell them the development costs of a new mirror including testing, all have changed their mind. Many custom options are possible it is just how much do you want to pay.
I see know potential benefit. We have actually tested SiO2 on the front surface for hydrophobic bonding to see if there was any additional bonding compared to the Silicon in the hard coating. So your thought process has been explored by me personally. Hard coating, AR thickness etc. are all important componates of a complete quality lens.
I would have to disagree. AR should not scratch as easily. In fact, it should raise the bayer ratio by some amount. The problem is the fact that the transmission is being increased, it makes scratches much more apparent.chip anderson:
Not to mention that front-side AR scratches a lot easier that a lens without same. People tend to get thier sunglasses in situations that are more likely to create scratches.
Chip
If you would just do it the right way from the beginning, this thread would not exist:
Polarized lenses, mirror coated, backside A/R, super-hydrophobic both sides.
No worries, no hassels, no reflections. Just pure, clear vision. I have 3 pair.
You hit the nail right on the head. There are a lot of labs that DON'T do it correctly.
I agree...Outstanding for those who finish only
There is hardly any benefit in just coating the back either! The light reflects off the front surface. The 2 percent you gained just got cut in half or worse. You can still see your own freakin eye on a 8 base poly lens! If the front side is AR coated it allows most of the back light to pass through. Take uncoated polarized samples, backside AR only, and both side coated and measure transmission values through the front, then through the back and you'll see what i'm talking about. Yes, I have done this personally. I also have done testing with putting Hydrophobics and Oleophobics on lenses without SIO2 and have found that the longterm adhesion was better with the SIO2 film present. This has to do with the design of the polymers used in the tests (we only used polymers that were in large scale use representing 70% of the Market), so their may be polymer designs out there that work fine with lacquer only.
Then you are using a bad coating! The coating increases scratch resistance. What if someone wants a mirror front, that'll really show scratches too! By that logic we shouldn't coat anything!!!!
Wow! Are you serious. I guess when you say something we should fetch Moses and run up to the mountain and put it on the stone tablets!
So you are saying that Backside AR doesn't increase transmission, but diminishes reflection? How's that work exactly?
This is not from the AR, but from the tint not being bleached back before its sent to the coating facility. The ultrasonic cleaning will bleach it back 10 - 20% if you don't do this. Then the degassing oven will also diminish the tint as well.
Did anyone ask about your specific products? You seem to make a lot of assumptions yourself, on lacquers and mirrors, of which there are many types.
Actually he said (or implied) that the purpose of a backside AR is not to increase transmission but instead reduce reflections. The really annoying reflections from behind will be reduced and you will also have fewer reflections from the back surface - front surface - eye route.
There are reflections on the front of the sun lens. If you remove those reflections the lens appears more transparent.
If you people would do what I do, this discussion wouldn't be taking place. Do it right the first time: as a professional, fit your patient/customer in a wrap frame, polarized lenses with a REAL hard coat, mirror the front (flash, solid, gradient, whatever) and be done with it. A good wrap will prevent backside reflections since light cannot reach the surface of the lens. If you don't wrap, then use backside A/R to reduce reflections. It is a sun lens- why are some of you even talking about increasing light transmission? If you want more light in the eye, use a gray or brown 'B' instead of 'C'.
The bottom line to the original query is this: backside A/R is beneficial, but not necessary. Professionals understand this, and do what they can to ensure that it is used when appropriate. (Use of it with a wrap is generally overkill.) One will find that whether the lens is polarized or not has some bearing on how important it is to use or not use backside A/R. Easiest way to resolve this issue for yourself is to try several different configurations. What you will find in the end, though, is that my suggestions are spot-on.
And by-the-way: if you are still tinting lenses to make sunglasses... shame on you!
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