Do the windows in a 172 provide any protection from the sun or is too bright? Particularly, if one wants to do a flying lesson and was told to bring sunglasses more than once. So, is it critical? My friend doesn't have sunglasses and would have to get prescribed ones which he can't get now. He got a gift of a flying lesson so he wants to try it but is being in the plane without sunglasses doable? Or will he be squinting the entire time? Or is it really bad for your eyes?
Definitely doable. No real protection from the sun just through the windshield but I flew a C172 for many years only using sunglasses occasionally. Just don't make the same mistake I did when I first started flying- paid a lot for a pair of polarised sunglasses then jumped in the cockpit and all the LCD screens went blank! :)
There are two main issues here: brightness, and UV protection. For brightness, it's really no different from being in a car. If the weather is cloudy or just not very bright then you won't need sunglasses in order to see. But if the sun is very bright, if you're flying over water or snow, or into the setting sun etc. then you would need them to see in exactly the same way that you would need them in a car (or on a boat) in similar conditions.
The UV question depends on the aircraft. Light aircraft windows are not made of glass and don't offer the same kind of UV protection that most car windows do. But they still do protect against UV and the bigger concern is apparently with glass windows found in larger aircraft that also fly higher where UV is more intense:
[...] glass laminate windscreens allowed higher levels of potentially damaging UV-A radiation to be transmitted than did plastic. Professional pilots who routinely fly at higher altitude for longer periods of time than private pilots should take special precautions to protect their eyes from UV exposure.
In any case, for one flight it won't matter at all, but if your friend continues to fly then he should really get a pair of sunglasses with UV protection. The FAA has a detailed pilot's guide to sunglasses here.
And as someone has already mentioned, polarized glasses are not recommended in aircraft because they prevent you seeing LCD screens clearly.
Sunglasses are not absolutely necessary when flying. I have flown the Cessna 172 with regular glasses only, and encountered no difficulty looking outside and inside.
If the area is covered with snow, it is better to wear glasses to protect the eyes though.
If you're flying during sunrise or sunset, better get them. On the Cessna 172, there is a shield (similar to that in cars) that can be unfolded from above if you encounter strong sunlight:
Although, some times even the pros can't bear it:
Nobody needs sunglasses, they are a just a convenience. They are very helpful for sure, especially in bright sunlight and hazy conditions, but not absolutely essential.
As for what to get you want non-polarized, and if you have require an eyeglass prescription on your medical the sunglasses will need to be that prescription.
No you don't "need" them but I would strongly advise them for a few reasons,
Not only do the front windshields of GA planes provide little UV protection you are flying at altitude and the higher you go the less natural UV protection you will get. Granted the change may me minimal it is still present.
Long exposure to bright sunlight can cause the eyes to tire out which can make it harder to see. You can actually get sun burn on your retina if you are exposed directly for to long. The last thing you want to happen when you are flying is to impair your vision in any way or simply get fatigued. That is when you start to make mistakes in a plane.
Who doesn't look great in aviators...
I also wear glasses regularly for distance (like your friend). When I started flying it was actually cheaper (or about even) to get fit for contacts and buy a nice pair of aviators than it was to get prescription sunglasses cut. I now don't have to worry about my sun glass prescription having to be cut or losing a very expensive pair of prescription sunglasses.
As mentioned I would NOT get polarized sun glasses because of the issues with glass cockpits. I have a pair of Ray-Ban aviators with the G15 (non polarized) glass and they are great. That being said I would also opt for more function over style here. Don't get half fade lenses or any of that stuff either it may look cooler but it wont provide any sun protection on the bottom half of the lens. You want something that provides good protection but still allows a good amount of light in as you will still have to read the instruments.
G15 is the traditional green glass that Ray-Ban uses in their sunglasses. It provides good protection with out the need for polarization. I suggested it because I also had a pair of the half fade Ray-Bans that I tried to fly with when I first started and they were terrible. They simply did not block enough light to be as effective as I wanted/needed them to be. The G15 provides a good amount of coverage with out using polarization and thus without interfering with glass cockpits if you happen to end up in that kind of plane.
I do not know how long you need to be exposed to get permanent eye damage but I tend to not play around with these kinds of issues, especially if it will permanently hamper my ability to fly. A decent pair of sun glasses be it Ray-Bans or any other of the popular brands may run you $100-$150 which pales in comparison to what you will spend getting your PPL.
It never hurts to bring your sunglasses along. Before getting in the plane, you'll do a visual inspection of the aircraft on the ground by walking around it and looking at things like flaps, ailerons, lights, etc. This usually happens on the ramp which is out in the open so it's an excellent time to gauge whether to wear your sunnies for the flight or not. At least, that's what I do.
It isn't that different from driving a car (or even better - riding a motorbike) out in open countryside, it depends mostly on the brightness of the day, the season, and how low the sun is in the sky. Not all planes have sun visors, so you'll definitely want your sunnies if the sun is low in the sky.
If you plan to do a lot of flying
AS/NZS 1067:2003 requires all sunglasses to meet minimum standards for glare, UV protection and colouration. All sunglasses sold are required to meet the standard. If you're in another country and plan to do a lot of flying, you'll want to check what laws apply to sunglasses (if any) and what UV and glare protection is provided by the glasses you intend to use.
The hazards associated with repeat, high-UV sun exposure to the eyes include inflammation, cataracts, eyelid cancer, retina degeneration and impaired night vision, so it's well worth protecting your vision with good quality UV blocking sunglasses.
Enjoy your flight!