Responding to a Question

As you may recall, I recently solicited all of you to find what it is you’d like to learn more about. Today’s post is responding to the first question:

Hello Optical Jedi!
Thanks for the question.
Last year I purchased a pair of sunglasses to wear while riding my bicycle – I got an Oakley Flak with “Prism Road” lenses, non-polarized. While the lenses aren’t quite as clear or sharp as I hoped they would be I’m very satisfied with them for bike riding because they differentiate the road surface well and keep my eyes relaxed while moving quickly from full sun to full shade. Also, they reduce a surprising amount of glare, and they are not so expensive that I would cry if they broke from a fall from the bike.

I thought I might be able to use them for driving too, but I’m not happy with them for driving. Although they reduce glare pretty well considering they aren’t polarized, they seem to make road signs harder to read. I think this may be because the grey tint is dark enough to reduce the contrast between white letters and their green or blue background.

So I’m about to buy a pair of driving sunglasses. I’m leaning toward polarized lenses, but not sure if the lens should be green, blue, or brown. What color works best for driving? What is the right percentage of tint? Are there other features I should get or consider?

Not sure if this matters, but I will need a progressive prescription lens.
Any thoughts?
Thanks so much!

-Reader chooses to remain anonymous

So this is actually an excellent question about lens colors and how they impact your visual experience.

Tint vs. Polarization

First, let’s start by talking about how lenses can be colored. The two main ways a lens can appear as a sunglass are tinted, or polarized.

TINT

A tinted lens is a lens that starts out as a clear piece of plastic (or polycarbonate, or high-index) and it is dipped in a hot dye until a color is absorbed. The major advantage of this process is that any color under the rainbow is possible. As well, any density of the color is possible. With some of the newer solutions in this category, like the PRIZM lens developed by Oakley, the process is more involved than this, using unite rare earth minerals to general the colors designed to enhance contrast. However, the basic premise is the same. This lens treatment is about generating a specific color, either for economy of cost on a sunglass, or to create a specific contrast experience to make the lens a better choice for certain activities (such as the aforementioned road cycling).

Tinting can also be used for non sunglass treatments, such as shooting lenses, or even the FL-41 tint which is specifically designed to help with reducing frequency of migraines (on an aside, I recently made these for my daughter and will do an article on this technology soon!). For the purposes of this article, I will save these alternative solutions for a later post.

One major disadvantage of a tinted lens is that it does not do anything to reduce reflected glare. By this, I am specifically addressing light that bounces off of surfaces, such as windshields, water, car hoods, etc. A tinted lens is not capable of addressing these issues because it is merely doing a color shift to either create a darker environment, or to increase contrast (and sometimes both of these things). A polarized lens takes a completely different approach to addressing sun protection and comfort.

POLARIZED

I have previously written articles about polarization where I have done a deep dive on how it is different, but for the sake of responding to the question specifically asked, I will direct you to my previous post for greater depth. Suffice to say, a polarize lens is not one that is dipped into a hot dye to generate the color you perceive. Instead, it is two clear pieces of lens with a film sandwiched between those two clear pieces of plastic (like the bologna in a sandwich of lens-bread). This film has some very unique properties which prevent light passing through the lens, unless the wavelength is traveling along the same plane as the film.

Now I know this sounds confusing. Even knowing what the technology is, as I read what I just typed I know I lost a few of you. And this is where things get a bit tricky. It’s much easier to visually present this. Light travels as a wave length in one specific direction forever, unless acted upon by some external force, e.g. a windshield. When light hits a surface, such as a windshield, it is deflected in every possible direction, depending on what part of the wave curve hits the surface. This scatters the light out in multiple directions and when it scatters it changes the wave angle as well.

microscopic lines in a polarizing film removed out-of-phase wavelengths of light

As you can see in the above graphic, the wavelength of light can only pass through the polar film along the vertical axis. If it hits a light scattering surface, like a windshield, then the light is heading at every possible angle. This means the wavelength is not just vertical, but also horizontal, and every possible angle in-between. But, if a polarizing film is put in front of that bounced light, the reflections are absorbed and reflected back by the film. Only the original horizontal wavelength is allowed through, eliminating the flash of glare and the mirror effect you can see in a windshield.

Now, if polarization has any signifcant drawbacks, they are these…the color choices for the film inside the lens are limited. Some newer options have hit the market for prescription eyewear recently, but for most patients, the only viable options are Grey, Brown, or G-15 (grey-green). In addition, LCD displays use a polarizing film to allow images to be seen. If that polarizing film in an LCD is set at 90 degrees from the film in your glasses, then the display is just black and you can’t see anything on it.

But What’s the Answer to the Question?

I cant hear you now. “But Ric, that’s all well and good, but what about the question your reader asked?” Well that’s a good question, and I’m getting there. You needed a basic understanding of the technologies involved before I could really answer the question.

I think maybe you’re starting to see why her non-polarized cycling glasses don’t work great for driving. When you have a windshield between what you’re looking at, the additional glare can dramatically reduce clarity and leave artifacts of reflection which can make things seem far less clear. But this only addresses the first half of the message. As to the question of lens color, We need to dig a little deeper into lens color theories.

As you’ve seen me mention for tinted lenses, there are specific colors designed to increase contrast. Generally speaking lens colors that are drifting towards reds, browns, or greens, dramatically boost definition between objects. For this reason, any time you’re concerned about contrast and definition (and driving is one of these scenarios in general), I recommend you consider a non-grey lens. The grey treatments tend to be the darkest, and depending where you live that may be the most critical component, but if you introduce a little color to the lens it will improve your clarity and contrast.

Comparison of world unfiltered and through the Maui Jim Maui Rose™️ Lens

Now I know you’ve all seen my self-professed love for Maui Jim, but this really is a place where I can’t stress strongly enough how the Maui Jim Maui Rose lens addresses all of these issues so perfectly. Maui Jim uses a proprietary mix of rare earth minerals to generate high contrast lenses which also enhance Red, Blue, and Green. the specific colors our eyes combine to generate every color we see. This means, that even when wearing a Rose colored lens which is dynamically enhancing contrast, colors are perceived as true and deeply vivid. This allows the eye to relax and not strain as much to see clearly.

Now, if you were to go with any other lens product (maybe the frames Maui Jim offers aren’t to your liking), then I would humbly suggest the keys are polarization, and a lens treatment besides true grey to maximize contrast and clarity.

Side note: I’m posting this from a optical convention I’ve been attending this week. I’ve been exposed to so much great content this week. Expect to see another article or two very soon on some great new innovations in our field!!

As always, this OpticalJedi post was created entirely by myself, Ric Peralta, and I have received no paid consideration for testing any product.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s