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is reflected sunlight bad to eye health?


kenny1999

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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?

 

 

 

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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.

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Posted (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 by kenny1999
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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. 

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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?

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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)

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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"!

 
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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 😉

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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?

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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.

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  • 4 months later...
On 1/3/2024 at 3:29 PM, 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.

I've lived in Sweden all life, so lots of snow. Don't know about the technicalities but it gets VERY bright when the sun reflects on larger areas of snow, not even sure if white is suffice as the color anymore by then

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I remember watching a BBC2 university programme years ago that said wearing sunglasses without side shields was worse than not wearing them at all. It stated that the dark lenses cause the pupil to expand,  thus increasing the angle of incidence for reflected light off the inside of the lenses to reach the retina. In bright, snowy environs the risk is significantly higher for uv exposure to the eyes.

Edited by StringJunky
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