Bright Sunlight We might be celebrating that the sun is shining, but sunlight can bring its own problems: Bright sunlight will be reflected off all sorts of surfaces, producing a lot of glare. Where there is bright sunlight, there is also likely to be deep shadows. The brighter the sunshine, the deeper the shadows will seem to be. The deeper the shadow, the harder it will be for you to be able to see into that shadow to see what is there. Wearing sunglasses seems to reduce the contrast between bright light and shadow. Polarised lenses will also reduce a large amount of the glare and reflections, allowing you to see through a windscreen, for example, to see what the driver is doing or about to do. In my opinion, glasses that darken or lighten automatically should not be worn whilst driving, because there will always be a delay in the change from light to dark, or the other way round. If you are driving in open ground in bright sunlight, then these lenses should have become darker. If you then drive into a wooded area, which will be in deep shadow, then the lenses will take time to become clear again. In the meantime you will effectively be driving in deep shadow, with dark glasses on, which cannot be safe. You cannot just take the glasses off whilst they adapt, if the lenses are prescription lenses.
Because wearing a pair of prescription glasses and sunglasses on top is not recommended, you should ensure that any sunglasses you may use will have any prescription lenses incorporated in them, but not be reactive to light levels.
Low Sunshine The winter sun will be lower in the sky than in the summer. For much of the day, the sun will appear lower in your wind-screen than your sun visor. Be prepared to be blinded by the sun as you turn a corner. Be prepared to slow down as you turn each corner. The sun’s glare will be made much worse if you have a dirty, wet, or misted windscreen. Try to keep both the inside and outside of the windscreens and windows clean and dry at all times. Always use a cloth to clean a window, so that your fingerprints don’t replace the dirt you have just removed. I have just been advised to buy some mentholated spirit to use on the windows. It seems to work really well and removing any marks or grease, though is definitely does smell for a while afterwards!
If you wear sunglasses (with prescription lenses if necessary) take them off whenever the sun goes in. They should not be worn in duller weather or at night as they seriously reduce the ability to see. And talking of prescription glasses... If you passed your driving test whilst wearing prescription glasses, you MUST wear them every time that you drive. Your licence will have a code on it, so the authorities will know whether or not you need to be wearing them.