kenny1999 Posted January 3 Share Posted January 3 We know that direct sunlight is dangerous to eye without any doubt. It's also widely said that reflected sunlight is also damaging, within a fraction of second. But I also find an ophthalmologist, whom I believe that it's verified, suggesting that there is no risk from diffuse, reflected sunlight. According to the link below https://www.aao.org/eye-health/ask-ophthalmologist-q/is-reflected-sun-light-dangerous What's going to be true? Is there any risk if I stare at the reflected sunlight from car for a few seconds? Link to comment Share on other sites More sharing options...
swansont Posted January 3 Share Posted January 3 2 hours ago, kenny1999 said: We know that direct sunlight is dangerous to eye without any doubt. It's also widely said that reflected sunlight is also damaging, within a fraction of second. But I also find an ophthalmologist, whom I believe that it's verified, suggesting that there is no risk from diffuse, reflected sunlight. According to the link below https://www.aao.org/eye-health/ask-ophthalmologist-q/is-reflected-sun-light-dangerous What's going to be true? Is there any risk if I stare at the reflected sunlight from car for a few seconds? Diffuse reflected sunlight is not all reflected sunlight. Specifically, it excludes specular-reflected sunlight. Anything that acts like a mirror is undergoing specular reflection. A car has lots of convex curved surfaces, so it probably reflects less light into your eye - you wouldn't see the image of the whole sun, which likely mitigates the danger. Also, look up snow blindness. A situation where diffuse reflection can be a problem. Link to comment Share on other sites More sharing options...
kenny1999 Posted January 3 Author Share Posted January 3 (edited) 1 hour ago, swansont said: Diffuse reflected sunlight is not all reflected sunlight. Specifically, it excludes specular-reflected sunlight. Anything that acts like a mirror is undergoing specular reflection. A car has lots of convex curved surfaces, so it probably reflects less light into your eye - you wouldn't see the image of the whole sun, which likely mitigates the danger. Also, look up snow blindness. A situation where diffuse reflection can be a problem. I have never lived or been to anywhere with a large area of snow, did you mean the image of the whole sun can sometimes been seen on the snow surface? What if a particular angle of a car where the reflected light is particularly strong? Which usually happens when the light hits directly on the glass of the headlight and reflects. Edited January 3 by kenny1999 1 Link to comment Share on other sites More sharing options...
swansont Posted January 3 Share Posted January 3 57 minutes ago, kenny1999 said: I have never lived or been to anywhere with a large area of snow, did you mean the image of the whole sun can sometimes been seen on the snow surface? No, it’s a diffuse reflection, but since there’s a lot of area undergoing reflection and not much to absorb the light, it’s very bright. 57 minutes ago, kenny1999 said: What if a particular angle of a car where the reflected light is particularly strong? Which usually happens when the light hits directly on the glass of the headlight and reflects. Glass transmits a lot of the light, and only reflects a lot at grazing incidence. Link to comment Share on other sites More sharing options...
kenny1999 Posted January 3 Author Share Posted January 3 1 hour ago, swansont said: No, it’s a diffuse reflection, but since there’s a lot of area undergoing reflection and not much to absorb the light, it’s very bright. Glass transmits a lot of the light, and only reflects a lot at grazing incidence. Sorry, what is grazing incidence? And so did you mean even if I believe that the reflected light from the glass cover of the headlight is strong, chances are it's completely safe even if I stared at it directly for a few seconds? Link to comment Share on other sites More sharing options...
studiot Posted January 3 Share Posted January 3 2 hours ago, kenny1999 said: I have never lived or been to anywhere with a large area of snow, did you mean the image of the whole sun can sometimes been seen on the snow surface? What if a particular angle of a car where the reflected light is particularly strong? Which usually happens when the light hits directly on the glass of the headlight and reflects. First I am going to say +1, for actually answering another member. First time that I can remember. Then I am going to say that light reflected off snow can lead to a conditions we call snow blindness. This is not permanent , means that your eye have been looking at a patternless reflection for too long. They will recover after closing them or looking away at something more normal for a while. Photokeratitis (Ultraviolet [UV] burn, Arc eye, Snow Blindness) - College of Optometrists (college-optometrists.org) Link to comment Share on other sites More sharing options...
Phi for All Posted January 3 Share Posted January 3 1 hour ago, studiot said: First I am going to say +1, for actually answering another member. First time that I can remember. ! Moderator Note This post has been reported as offensive. If you don't STOP giving kenny1999 positive reputation and encouragement to reply to other members, you will be punished again as a "hater"! Link to comment Share on other sites More sharing options...
swansont Posted January 3 Share Posted January 3 2 hours ago, kenny1999 said: Sorry, what is grazing incidence? And so did you mean even if I believe that the reflected light from the glass cover of the headlight is strong, chances are it's completely safe even if I stared at it directly for a few seconds? Light hitting at a large angle, as measured from normal (90 degrees). It just “grazes” the surface Reflection at 90 degrees (called normal incidence) reflects about 4%. As the angle increases it goes up for parallel polarization, and drops for the perpendicular polarization (it goes to zero a Brewster’s angle, where all light is transmitted) and then increases. Out at 70+ degrees reflection is quite strong, but it would be difficult for you to have sunlight reflected into your eyes at a large angle. 1 hour ago, studiot said: Then I am going to say that light reflected off snow can lead to a conditions we call snow blindness. I wish I had thought to mention that 😉 Link to comment Share on other sites More sharing options...
kenny1999 Posted January 4 Author Share Posted January 4 10 hours ago, swansont said: Light hitting at a large angle, as measured from normal (90 degrees). It just “grazes” the surface Reflection at 90 degrees (called normal incidence) reflects about 4%. As the angle increases it goes up for parallel polarization, and drops for the perpendicular polarization (it goes to zero a Brewster’s angle, where all light is transmitted) and then increases. Out at 70+ degrees reflection is quite strong, but it would be difficult for you to have sunlight reflected into your eyes at a large angle. I wish I had thought to mention that 😉 Did you mean since the car surfaces are usually roughly finished so light is reflected at a lot of angles so the intensity is largely reduced at any particular angle, and the likelihood of causing retinal damage or eyes is when a lot of light is focused at one angle? Link to comment Share on other sites More sharing options...
swansont Posted January 4 Share Posted January 4 6 hours ago, kenny1999 said: Did you mean since the car surfaces are usually roughly finished so light is reflected at a lot of angles so the intensity is largely reduced at any particular angle, and the likelihood of causing retinal damage or eyes is when a lot of light is focused at one angle? They can have a rough finish, but it's more that they have curved convex surfaces, so even with a glossy finish, the light diverges upon reflection. 1 Link to comment Share on other sites More sharing options...
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