Serious Sun-Glass

[Robert Atkinson 2Participant @robertatkinson2]

Bernard has mentioned something I was about to warn about.

Don’t use polarised glasses when driving a modern car. The LCD displays rely on polarised light to operate. Depending on how thai aligins with your glasses ti cn prvent you seeing the display / dashboard. Also affects some phone / computer / TV screens. Thia has led to a reduction in popularity of polarised lenses.

Dave,
I’ve seen that done, both mechanically and electronically (liquid crystal) on aircraft cabin windows but never on a pilots visor. Do you know what aircraft this was on? I assume it was sometime ago as on modern aircraft there are issues with LCD displays and possibly Head Up displays (HUD).

Michael,
Very glad you are going to take professional advice.

Robert.

[bernard towersParticipant @bernardtowers37738]

Strange thing is my prescription sunglasses are not polarised!!!

[duncan webster 1Participant @duncanwebster1]

The Dambusters used blue filters on the cockpit windows and amber googles for the flight crew so that they could see the instruments but even in daylight the outside looked dark. I’m not sure what the police would make of that if Michael trued ig on his car.

[Robert Atkinson 2]

On Robert Atkinson 2 Said:

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I’ve seen that done, both mechanically and electronically (liquid crystal) on aircraft cabin windows but never on a pilots visor. Do you know what aircraft this was on? I assume it was sometime ago as on modern aircraft there are issues with LCD displays and possibly Head Up displays (HUD).

It’s mentioned in one of my schoolboy books on the wonders of aviation circa 1960.  No details or a picture, but I guess more likely to have been googles than a wrap-around type.

Not sure about the advice to avoid polarising glasses whilst driving. Car instruments aren’t safety critical, but driving along a wet road into the rising or setting sun is!  That’s when I wear them.

I wonder if ordinary glasses are frequency sensitive, and might block LED light disprortionally. Cheap glasses tha block visible light but not UV are famously bad for the eyes.  Fooled into thinking it’s dim the iris opens and lets UV into the retina at full blast.

I’ve read that sunglasses are rarely necessary in the UK (normal eyesight adapts) and they cause accidents.  The auto-darkening type take so long to clear that drivers go blind for minutes at a time.  I’ve even seen drivers wearing them at night.  Poseurs…

Dave

[Michael GilliganParticipant @michaelgilligan61133]

For what it’s worth … I asked Google about the original ‘privacy glass’ in my Vitara:

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The reason for so-doing was to get some sort of baseline for my discussion with the  Optician.

I have noticed that my rear-view via the mirror and the privacy glass is [when also using the sun-glasses] reasonably comfortable.

Pretty meaningless without a spectrometer and a photometer to hand, but it might give us some hints.

MichaelG.

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P.S. __ for completeness

I found the tag from the Foster Grants

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[Michael GilliganParticipant @michaelgilligan61133]

Here’s a useful reference document that might be of general interest:

 

https://www.abdo.org.uk/wp-content/uploads/2012/04/Eye-protection_safety-and-protective-eyewear.pdf

MichaelG.

[duncan webster 1Participant @duncanwebster1]

I made the mistake of getting reactolite lenses many years ago. Up a mountain in winter, thick mist, freezing cold. Reactolites pitch black. Fortunately i can see well enough to mznagd without, especiallg as i cojldnt see mord thfn 50 meyres eigh ghf mist anyway. According to the optician, sensitivity goes up as temperature goes down, and whatever wavelength triggers the darkening goes straight through mist. Scrapped the lenses.

[Robert Atkinson 2Participant @robertatkinson2]

Dave,

A lot of materials can have unexpected optical transmissin characteristics. Some that look clear e.g. normal glass block a lot of UV and some IR while some that are opaque to visible light and look black pass UV (woods glass) or IR (“black” acrylic). Polycarbonate and acrylic block most UV but some common resins used for spectacle lenses e.g. CR-39 don’t. So clear safety spectacles block UV but sunglasses may not.
I know one manufactuer, Ray-Ban IIRC, had a specific “tint” for drivers that had a “hole” in the red portion of the absorption spectrum so brake lights and red traffic lights stood out.

I once had troule getting a machine with an internal 254nm UV light and a lightly tinted acrylic full width “door” past a UL (USA insurance recognised safety standard) approval inspection. The inspector would not accept that the plastic blocked UV dispite being shown data from the manufacturer. He was worried about exposure to users. I had to go and buy a UV photometer to prove there was no detectable UV. I even had a couple of plastic samples. One thinned to 10% another with a several 1mm holes drilled in it. Neithe passed any measurable UV. After the inspector signed off the machine I pointed out the OSHA (US health and safety) has no exposure limit for UV radiation to workers or public…

Only a transmission spectrophotometer will tel lthe whole story.

[Michael GilliganParticipant @michaelgilligan61133]

I am hoping for an interesting and productive visit to my Opticians tomorrow, and will of course report back.

My current working hypothesis is that the problem relates to Violet rather than either of the UV bands.

For a glimpse of  my logic, see the Foster Grants tag and also my earlier note to Kiwi https://www.model-engineer.co.uk/forums/topic/serious-sun-glass/#post-797264

… I’m guessing I might end-up with Amber [i.e, Violet-blocking] filters.

 

MichaelG.

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Edit: __ modern dichroic filters are astonishing !

https://www.edmundoptics.co.uk/document/download/396611

https://www.edmundoptics.co.uk/f/additive-and-subtractive-dichroic-color-filters/11985/

[Robert Atkinson 2Participant @robertatkinson2]

Those are pretty basic filters. The high perfomance ones have passbands of a few nm. The price is mugh higer though. I have quite a selection of them that were used in various fluorescent imaging and measurement instruments. This is a basic one https://patents.google.com/patent/US6878949B2/en
I’m back in aerospace now so little use for the filters. I did try a green one on a replacement lamp for my H&W autocollimator but a highe powe LED was much better.

Robert.

[Kiwi BlokeParticipant @kiwibloke62605]

Michael, you’ve probably got there already, but there is quite a bit of info. on the ‘net about the transmission characteristics of the human eye’s lens (and other components of the eye), and age effects. Here’s just one: https://iovs.arvojournals.org/article.aspx?articleid=2129060

It seems that the transmission characteristics of replacement lenses varies with type. You should be able to discover the characteristics of that with which you have been fitted. Perhaps that would allow a better tailored filter for your ‘shades’.

Regarding the warning about polaroid and driving… In bright sun, I find the reflected image of the top of the scuttle interferes unacceptably with my view through the windscreen in some vehicles, one of the worst being our Jazz. Polaroid sunglasses therefore become a necessity! Since mine do not have ‘progressive’ lenses, they produce two mechanisms making the reading of the speedo., etc. a bit of a problem. I think being able to see forwards is a bit more important…

[V8EngParticipant @v8eng]

I shall be very interested in the outcome of your visit to the optician.

My wife and I had cataracts done in both eyes about 4 years ago.

We used the same consultant and hospital but my wife has become hyper sensitive to bright light and needs to wear sunglasses very frequently but I do not have issues with bright light.

The consultant appeared rather puzzled by my wife’s problem whereas the optician thinks that the issue is partly caused by weakening of the muscles controlling her iris and is somewhat age related.

As an aside my new lenses claim to restrict both uv and blue light.

Unfortunately my wife cannot currently locate the card for her lenses but I am quite convinced from memory that they are of the same make and type as my own.

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