Re: cataracts, night vision & "night glasses"

In article <9vGdnSz-M-(E-Mail Removed)>,
nobody <(E-Mail Removed)> wrote:

> I'll be having cataract surgery & have read info on cataracts & its
> effect on limiting night vision. Wondering if the yellow tinted
> "night driving glasses" will help with night driving.
>
> I guess the night driving glasses may cut down glare but have doubts
> about the visibility of objects.
>
> Anyone know or have experience with the night driving glasses that
> is being advertised?

I am not a health professional. My background is in optics.

Most eyeglasses DO NOT cut down on glare compared to light useful for
vision. Polarized lenses can do so at the expense of losing more than
50% of the light. They can cut down on some glare reflected off of the
road, especially from the sun at some times of the day,

Yellow tints can improve contrast under some circumstances. That is why
they used to be used a lot in black and white photography.

All in all, my educated guess is that you want all the light you can get
when driving dark roads at night. I would be open to changing my mind if
presented with experimental data showing benefit. Watch out for sellers'
hype.

Bill

In article <(E-Mail Removed)>,
nobody <(E-Mail Removed)> wrote:

> I was wondering since the AR lenses is supposed to allow more light to
> come thru. On a website that had a before & after effect of AR, I felt
> that I saw more objects without AR than with AR; I attributed that the
> glare bounced more light to the object (person) standing next to the
> car even if the headlight was glaring. I got AR lenses anyway......
>
> I need to trackdown that website as it could have been my old monitor; but
> if I can see more things with glare than without, glare is the way to go.

I read your post twice and still have some trouble understanding what
you are trying to say. For ordinary glass and typical plastic, about 4%
of incident light is reflected and lost from each surface or 8% from the
front and back of the lens combined. That is not really very much. The
problem often created is that the reflections cause unwanted images and
confusion. In photography where there can easily be six to eight
glass-air interfaces in a lens, that can be a lot of light loss and
degradation of the image on the film or sensor. In photography, that is
called flare. Certainly a bright light behind you can reflect off of
your lens surfaces into your eye.

There are many different kinds of AR coatings. I am not very familiar
with those use on eyeglass lenses. The simplest ones will reduce
reflectivity to about 1% per surface. Many more tricks at greater
expense can be performed using multilayer AR coatings. Is it worth it? I
think that is highly subjective.

By the way, multilayer coatings can be used to color glasses,
particularly sunglasses. That usually ends up reducing transmission
through the lens be increasing reflectivity at some wavelengths.

Bill

In article <(E-Mail Removed)>,
nobody <(E-Mail Removed)> wrote:

> The website had 2 pictures displayed to show how much more one can see
> with AR coated eyeglasses; a thread a few years back said that there was
> more light getting thru a pair eyeglasses using AR coatings.
>
> Now, the website's pics was a headon shot of a car at night with the
> headlights on & a person standing back by the door. With AR coating,
> the area around the headlights do show up clearer BUT, from my perspective,
> more of the person was visible in the pic without the AR coating.
>
> So, I'm just guessing that flare is making the more of the person visible
> when not AR is applied if all else was equal. Don't really understand
> why that is so; could be psycological that when objects are "brighter", it
> appears that one can see more. My AR coated lenses seem to make objects
> less "bright" so that it seems that the objects are "dimmer" than when
> glare/flare is present.

You are probably attributing too more capability to the practice of
photography than is justified. For example, in viewing a computer screen
in a subdued light environment, AR coatings have little to offer. The 8%
loss in transmitted light signal is virtually insignificant. On the
other hand, scattering and multiple reflection from lens surfaces can
give a noisy background that makes it very difficult to see what is near
a headlight pointing at you.

Bill