Questions tagged [vision]

Physical processes involved when seeing, and comparisons between with other light detection systems. Includes questions about the eye, optical nerve, brain, corrective lenses, etc.

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Testing UVA and UVB protection in sunglasses?

Is there an inexpensive way to test UVA and UVB protection in sunglasses? (Or does all plastic block a majority of UVA and UVB light?) This question was posed by another StackExchange user in the ...
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1answer
110 views

Is visible light really visible? [closed]

As we know, colors only exist in the brain. How can we see light if it has no color? Our eyes detect light, but seeing occurs in the visual cortex. Is visible light really visible?
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239 views

Why do things seem smaller when seen through spectacles?

When I see through someone's spectacles, things seem very small to me? Why does it happen? Do people wearing spectacles see things smaller than we do?
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3answers
775 views

Why does looking through pinhole change the eyes focal length?

Normally the comfortable viewing distance for small text on my phone is around 20 to 30cm much below that and details start to get fuzzy. However looking through a pinhole (hole punctured in a thick ...
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1answer
316 views

Why is eye accommodation necessary?

Why is eye accommodation necessary when infinite number of light rays come from a specific point of an object and we can use any pair of rays we need and the curvature of the lens need not to be ...
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1answer
591 views

How much light does the sun emit in the violet spectrum? [closed]

According to wikipedia: "UV radiation constitutes about 10% of the total light output of the Sun, and is thus present in sunlight" It also states that "at ground level sunlight is 44% visible light, 3%...
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Predict Spectral Composition of Light via the Color Temperature

If I know the color temperature of a given source of light is it possible to predict the spectral composition of the light (in other words the specific wavelengths / frequencies that make up the light ...
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215 views

Does Blue Light Really Have a Dark Side?

I was reading the following article on Wikipedia which discusses the dangers of blue light: Blue-light hazard is defined as the potential for a photochemical-induced retinal injury resulting from ...
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1answer
203 views

Danger to Expose Eye to 10,000+ Lux of Ultraviolet Light

Is it dangerous to expose the human eye to 3,000 - 10,000+ lux of UV (ultra violet) light in the 380 - 400 nm wavelength? I understand anything below 400 nm is tech classified as UV/UVA radiation ...
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1answer
313 views

If light carries its energy in discrete packets, why don't we see a series of flashes when we look at things?

According to the photon model, light carries its energy in packets called quanta or photons. Why then don't we see a series of flashes when we look at things?
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Viewing totality though an unfiltered telescope [closed]

DISCLAIMER: This question is for informational purposes only and the ensuing discussion must not be construed as safety advice. There seems to be a consensus among experts that partial eclipse should ...
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1answer
2k views

Is looking at an eclipse worse than looking at the sun? [duplicate]

I understand why looking at the sun is bad. I also understand that looking at the eclipse is bad. Is it more dangerous to glance at an eclipse than the sun, assuming you avert your eyes right very ...
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1answer
636 views

How does the Sun burn a crescent shaped scar in your eyes during a solar eclipse?

I was listening to NPR this morning and a man talking about the solar eclipse said that you cannot look at even a sliver of the sun because it could still damage your eyes. He noted he's even had ...
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Why aren't 100% UV blocked sunglasses safe to view an eclipse with?

I am not planning on staring into the sun during an eclipse or any other time. I have been reading about how no variety of regular sunglasses are safe enough to view the eclipse with. I'm not talking ...
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1answer
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Why can I look at the sun with my sunglasses but not at the solar eclipse?

Is the problem with seeing an eclipse that you have a sudden change between penumbra and regular sun? If that's the case, why can I look to the sun with my sunglasses on but I can't do it in an ...
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2answers
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Can two polarized glass filters held at near 90° orientation serve as safe eclipse glasses? [closed]

Using two polarized filters to block all (?) light is a common classroom demonstration. With the imminent north American total eclipse, the media has been pushing eclipse glasses and emphasizing the ...
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Can our eyes and ears detect phase information in addition to amplitude and frequency information?

Both eyes and ears detect continuous waves that impinge upon them - electromagnetic waves in the case of eyes, and sound air pressure waves in the case of ears. The amplitude of these waves is ...
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6answers
9k views

Does pure yellow exist in variations we can't discern? [duplicate]

If you add red light (~440 THz) and green light (~560 THz), you get what we perceive as yellow light (~520 THz). But I assume what you really get is a mixed waveform that we perceive as yellow? ...
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2answers
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Are we always inaccurate or relative about the real size of an object?

So basically the further we are, the smaller an object appears and as we get closer to it, it enlarges progressively, is it so that the size of an object is always relative and that we can never ...
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4answers
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Seeing something from only one angle means you have only seen (what?)% of its surface area at most?

Is there a logical/mathematical way to derive what the very maximum percentage of surface area you can see from one angle of any physical object? For instance, if I look at the broad side of a piece ...
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2answers
2k views

Does breathing on your glasses help with cleaning?

I noticed people who wear glasses clean the lenses by first breathing on them and then wiping it with something like a tissue or cloth etc. Does this actually help?
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2answers
50 views

If someone were to put really small objects 10x spaced on a background, would they see the objects or the background?

If someone were to put a sheet full of 1 micron x 1 micron black squares as a grid on a white piece of paper, and spaced them 10 microns apart (up-down, left-right, obviously diagonal doesn't count), ...
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1answer
33 views

It's easy to 3d model a room via binocular vision, can it be done with 2 microphones and a beeper?

Many algorithms exist to construct a 3d model from two cameras, is it possible to 3d model of a room via a speaker that produces a beep, and two microphones with arbitrarily good hearing skill (ie can ...
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1answer
212 views

Why do objects that are further away seem closer? [closed]

I am outside and am walking to my house from my car that is across the street. I get in my house and look out the window and my car seems like its right in front of my window. Why is that?
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1answer
139 views

If our eye lens and cornea were flat would we still receive the world upside down?

Usually the effect of a pinhole (or camera obscura) and the lens of our eyes are creating the world upside down on our retina. Now imagine the lens and cornea would be flat is the pinhole effect ...
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1answer
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Why does the visual field not appear like a blend of light?

If, from any given point on an object, light is scattered in many directions and all of these light waves (within the visual field) pass into ones eye, then how do objects appear distinct? Why does ...
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1answer
2k views

How is Hue, Saturation and Brightness of colours explained via EM and QED?

Light is a electromagnetic wave and its wavelengths determines the colour of the light, so that would be the Hue. But what determines the Saturation. The less saturated a colour is the more greyish ...
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1answer
355 views

Why does light have only 3 primary colours and why don't then non primary VIBGYOR colours disperse? [duplicate]

While light has so many wavelengths why only 3 colours exist as primary colours? Why do some colours disperse while VIBGYOR colours don't (except the primary ones which satisfy the logic as they are ...
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1answer
2k views

Ray diagram of focussing on a compound microscope

When we use a usual biology class compound microscope, we need to focus the stage (place the object) to the "correct" position. It is just in that sweet spot that the image is sharp and clear. So we ...
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1answer
80 views

How do cone cells perceive the wavelength of light waves?

Everywhere I look on the internet, I find this answer: "Cone cells perceive light." But I would like a more fundamental explanation. How do cone cells perceive and differentiate between these ...
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Do prescription glasses augment or mitigate the effect of the sun on the skin around the eyes directly beneath them (assuming no UV blocking coating)?

The question is about minus correction (nearsightedness), but would also be interesting to know how it differs for plus correction (farsightedness), cylinder correction (astigmatism), axis correction.
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Why does a yellow object turn white under a yellow light? Shouldn't it turn yellow instead?

Recently I was eating a yellow rice for lunch in a restaurant with only yellow lights. But the rice looked white! I was intrigued by this because I always thought it should look yellow since the ...
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Inverting Horizon?

everyone knows that looking at the horizon at something going far away, the last thing you see from it is its top, but what if you had a ground going up very very very slightly and something moves ...
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Light Intensity vs Visibility/Brightness?

I am curious about something that doesn't seem to be pointed out very much. This is the double-slit intensity pattern as a graph: This is what you're supposed to see in real-life: If you look at ...
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1answer
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Make a projected image smaller?

A friend has a Batman nightlight that projects Batman onto her ceiling. She has vision problems because of a head injury. She could see Batman fine when she was in an upstairs bedroom and the ceiling ...
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How many photons enter our eyes per second when looking at the blue sky on a sunny day?

How many photons enter our eyes per second when looking at the blue sky on a sunny day? Say the sun is directly over head and you are looking at the blue sky on the horizon. Say that the pupil is 2mm ...
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1answer
341 views

Why is “Visible Light” in the middle of the spectrum and not at an end?

I realize that the spectrum is man-made, and "visible" is a human-relative term. However, the scale is based on objectives, such as frequency and wavelength, and "visible" light is objectively unique ...
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LED headlight illusion

Commuting today, I noticed that the car behind me had LED headlights that appeared to "bobble" within their lenses--in other words the reflection of the car and the reflection of the headlight lamps ...
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Why do we see vertical lines when we close our eyes into slits?

When we close our eyes into small slits and look at a light source we see vertical lines of light coming out. Why does this happen? Is it something to do with our eyelashes or is it because of ...
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11k views

Why can we only “see” reflected light? [duplicate]

This is a question thats been bothering me a while. I don't even know if it makes sense or not (like if it is a physics question or becoming a philosophical one). But here it goes. The crux of my ...
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2answers
3k views

How is light able to form images? [duplicate]

Everyday we see ourselves in mirror and this is due to light which forms our image after reflection ( may be refraction sometimes) . But I wonder how can light carry the image. How is it possible that ...
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1answer
970 views

Why can't we see electrons with our naked eyes?

Why can we not see electrons or any other subatomic particle with our naked eye, without using any apparatus?
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70 views

Why isn't everything a glowing blob if light reaches us from all directions

I was thinking about light, and then I realized that if light is travelling in all directions form all sources (either emitted or reflected) everything should be merged together in a big light blob. ...
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Musical notes and colors of a rainbow

I have wondered that in an octave in piano there are seven primary notes, and also we observe mostly seven primary colors of a rainbow. I know we perceive logarithmically, that means we only care ...
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Why are distant lights more flickery in peripheral vision?

I have just realized that if you arrange your angle to a flickering distant light source and make it fall into your far-peripheral vision (+70 degree to the side of your FOV), you perceive it to be ...
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What is Curvature of eye lens?

I wanted to know what do we mean by "curvature of eye lens", is it the reciprocal of $r$ i.e $c=1/r$ or is it synonymous to radius of curvature of the eye lens. Moreover how does aperture relate to ...
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2answers
395 views

How does a colored glass work?

If I look through a colored glass, I see all the objects colored as the glass. Why? How does the color of the glass transfer to the image?
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1answer
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Can a short-sighted person see a target 'better' than someone with no impediment, if target is very close?

Can a short-sighted person with no corrective appliance see an object more clearly than a person with no impediment, if the object is at an optimal distance for them (i.e. closer than the unimpaired ...
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2answers
394 views

Physics about Seurat's painting [closed]

The following figure is Georges Seurat's work: A Sunday Afternoon on the Island of La Grande Jatte,created by the technique known as pointillism, in 1884-1886. This painting consists of closely ...
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If I can see someone's eyes, can they see mine?

Besides the obvious cases where I'm behind a "one-way" mirror or have goggles/glasses on: is there one where I can see someone's eyes, and they can't see mine?