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Questions tagged [visible-light]

Questions related to the perception and measurement of light (primarily in the visible range), its mathematical description, the reproduction of colors by different means, color combinations, etc. Please use the tag [electromagnetic-radiation] if you want to refer to the general form of light.

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27 views

Is there any time difference when we see distant a object? [duplicate]

I was just wondering that We see objects thru our eyes and light has to reach our eyes so that our brain can process that light. But then there must be a time difference between that object which I ...
3
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4answers
60 views

Why does frequency remain unchanged in light refraction but wavelength doesn't? [duplicate]

Since the frequency of an electromagnetic wave does not change during refraction but the velocity changes, the wavelength must therefore change. But why doesn't the frequency change in the first place?...
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1answer
27 views

The time it takes light to reach different points on a plane

Imagine there is a light source which is held perpendicular to a plane. Is there a difference in the speed light hits a part of the plane?
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0answers
12 views

Write some applications of colour subtraction [on hold]

Write some applications of colour subtraction. I know color subtraction like: White-Blue =Green + Red= Yellow, etc... Please mention some applications of colour subtraction.
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2answers
93 views
+100

2 windows - will I see the reflections?

I have a question regarding photons nature. Let's say I have a single source of light - regular bulb and the observer - in the same room. The observer looks through a glass window (normal glass ...
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1answer
46 views

How do photons encode images?

When light bounces off an object, the light then travels into the eye of an observer who can then reconstruct the image. Do the photons encode the image and how do they do so?
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1answer
19 views

Speed of light in vacuum in non-inertial frame [duplicate]

Does the speed of light remains $c$ also in non-inertial frames? Or it changes from frame to frame?
3
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1answer
55 views

Why does light show a no interference result?

I was reading the first chapter in the Feynman lectures volume 3 about quantum mechanics and I understand the concept that 'interference' means $P_{12}=P_1+P_2$ as expected, however when the electron ...
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2answers
23 views

Radio Waves / Light: Atmospheric Refraction

The following image differentiates between a visual horizon and a radar horizon. Sidenote: I'm not too familiar with primary surveillance radar technology, but this image refers to secondary ...
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2answers
93 views

How does a photon impart it's colour to the retina in the instant that it makes contact? [on hold]

Considering the speed of light, any number of photons carrying the same colour frequency and hitting the retina at the back of an eyeball would be at varying phases in their respective cycles, but ...
2
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1answer
28 views

Where does energy come from when a laser bean exits lens at c?

Take a laser. Fire it at a lens. Prior to arrival at the lens the lasers pulsed beam’s speed is c. Traversing the lens it’s speed is less than c. Exiting the lens (and back to the vacuum) it’s speed ...
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0answers
32 views

Is it possible to manipulate the polarization of unpolarized light within a medium via Electric field?

You see this setup above. There is an unpolarized light source travelling through a transparent dielectric medium. Think of this triangular shaped medium as a capacitor. there are 3 conductive sides ...
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1answer
53 views

Would 2 people wearing identical night vision goggles be able to see each other from afar? [on hold]

From what I understand, this is how night vision goggles (NVGs) function: The environment is illuminated by forward facing IR LEDs. A portion of the light bouncing off of the scene passes through an ...
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3answers
96 views

Does light take the path of least time because it travels in straight lines or vice versa?

My question is which of these two feats is a consequence of the other? Light travels in straight lines, mostly. Does it do that as a result of Fermat's principle of least time? and if so, is there a ...
2
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1answer
40 views

Brightness of colors

I have 1W lights, red and green. If I turn the red light full power I get 1W red light, if I turn green light full power, I get 1W green. If I want to mix the lights and get yellow light, which has ...
3
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1answer
43 views

Bubble optics, impact

My 8 years old daughter was blowing soap bubbles. Most of the bubbles had color. She randomly choses a bubble with colors and lands it on the wand. Instantly it's color is gone. If she blows this ...
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3answers
85 views

Four-velocity vector of light

Please note that my question is not a duplicate, it is not about the speed of light, my question is only technical about the four velocity vector for light, its definedeness, value and constantness. ...
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2answers
83 views

Can radiation light up a fluorescent light?

Watching the excellent but horrific HBO Miniseries Chernobyl. There is a scene where the radiation level is so strong, it ruins the batteries of flashlights being operated inside the plant, in the ...
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2answers
205 views

How bright was the universe after Big Bang during photon epoch?

After 10 seconds of Big Bang, most of the leptons and antileptons annihilate each other leading to an outburst of photons. The universe was said to be dominated by photons resembling a glowing fog. ...
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0answers
19 views

Could ultrasound pings and triangulation really help de-scatter diffuse red light for imaging?

Does the science explanation in the latest OpenWater TED talk make sense in principle? The claim involves taking advantage of the doppler effect. Could someone give a more detailed explanation as to ...
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2answers
44 views

How do lens capture reflections clearly?

In an optical system which uses lenses (cameras, our eye) multiple rays from the same point are conveyed in a single point on the retina / image sensor. This is typically shown as in the image below. ...
2
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2answers
233 views

Are there any types of lasers that emit orange and yellow light?

That is, without the introduction of nonlinear optics for frequency multiplication. In the case of orange light, I've often wondered in orange minerals like Lead Molybdate (PbMoO4) fluoresce the way ...
4
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2answers
55 views

Why aren't maximums at 1 wavelength for single slit interference?

I can understand why there are destructive points in single slit interference. It is because the path length difference between the "pairs" of rays have a path length difference of $\lambda/2$. What I ...
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0answers
35 views

Cherenkov radiation relativistic correction

I have to write a paper on Cherenkov detection. And got a bit of an issue on the relativistic particle/recoil correction of the Cherenkov angle formula. Normaly $$cos( \theta_c) = \frac{1}{n\beta} $$...
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0answers
11 views

Light traveling through ice and glass and then lightsensitive film

I’m not a physician but I’m facing a physical issue in producing some images. My light source is a photographic enlarger - light is coming through a lens. That light travels through ice, then glass ...
2
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2answers
98 views

Photons’ Speed (light speed) in vacuum [duplicate]

In a vacuum, are photons always traveling at 100% light speed? Can photons go any slower in vacuum? They have no mass which means they can go at 100% light speed, but do they have to?
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4answers
58 views

Can you change the wavelength of light keeping frequency constant and can you do the opposite as well? [duplicate]

Can you change the wavelength of light keeping frequency constant and can you do the opposite as well? I understood the basics but please don't hesitate to go deeper into the concept. Also, If you ...
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1answer
42 views

Visible light as fraction of the EM spectrum

I was asked today what percentage of the EM spectrum we can see. It looks like a simple question, and yet I don't know how to answer it. I know that the visible light has wavelengths between $3.8 \...
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3answers
130 views

Why is grass green? [closed]

How come grass isn't blue or pink, but apparently, it is according to this scientist it is every color but green. I also got told by my teacher that grass is only green and no other color. So I am ...
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0answers
11 views

Determine whether a mirror is convex or concave from image magnitude, distance and reality

An object is placed 1.5m in front of each of three mirrors, (i), (ii) and (iii) with the following results: i) The image is real and 1.5m from the mirror. ii) The image is virtual and 1.0m from the ...
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0answers
173 views

Building the Penrose Unilluminable Room [closed]

As an architect with an interest in the natural sciences I was intrigued when I first learned of the illumination problem and its proposed solutions, specifically the one proposed by Roger Penrose in ...
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1answer
28 views

Refractive index and optical fibre question

This is an A level AQA question: A signal is to be transmitted along an optical fibre of length 1200m. The signal consists of square pulses of white light and this is to be transmitted along the ...
2
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1answer
28 views

What kind of light coherence is required for an image

If 1- Optically speaking, an image point (or pixel) is a light interference pattern 2- interference patterns require phase coherence then 3- the source of the image point must emit coherent light ...
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1answer
5k views

How does the anti-gravity fountain work?

I just saw this video of an anti-gravity fountain on youtube, but I can't understand how you can reverse the flow of water. I know you can stop the flow of water by using something called a ...
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2answers
54 views

Why are there rings (halos) around street lights? Especially when it's foggy

I was in a car that was turned off last night for some time and the windows became foggy via condensation (moisture droplets building up on one side of window). Looking outside, I could see that ...
4
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3answers
188 views

How many yellow objects are there? [closed]

I thought and read about color mixing today. I made some counterintuitive discoveries, and i now have some thought experiments which i cannot test. I could print a yellow image but i use a different ...
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3answers
104 views

How does a wave become a color?

I am a mathematician and not a physicist, so please be gentle to me. The best explanation I found so far about light waves was here: https://youtu.be/7eutept5h0Q If I got it right, then light is a ...
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3answers
48 views

How does one perceive light in terms of value?

I'm coming from learning art, and I'm trying to figure out the way light perception works. If I got it right, in order to see the surface, it has to reflect rays of light in viewer's eyes, but the ...
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1answer
24 views

How to find absolute luminance of a pixel in a photo?

Suppose we have a photo camera, which can take photos from which we can find out relative luminances of various pixels. Suppose also that we can vary exposure times so as to measure scenes of very ...
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6answers
103 views

Can an electromagnetic wave travel less than the speed of light and yet perceived by the eye as a light?

When an electromagnetic field passes through different mediums, it is known that it will refract. And during refraction - since its frequency is kept constant - the only parameter that changes is its ...
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0answers
38 views

Do virtual images exist in the real world? [duplicate]

I have been reading an article here in physics stack exchange that talks about if it is possible to see virtual images, and i read an answer saying it is actually your brain that understands the ...
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1answer
41 views

What does the person looking from the point of the image which is behind see?

In a plane mirror, the image of an object is virtual and is behind the image of another object. What does the observer looking from the point of the image which is behind see?
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1answer
73 views

Thought experiment: if an observer can travel at the speed of light [closed]

What would the observer see if he could travel at the speed of light and shot a photon beam at the same time?
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0answers
18 views

Crookes radiometer showing radiation pressure

Originally, the Crookes radiometer was meant to measure the light intensity. For decades the explanation for its rotation was debated. It is now known that the rotation does not originate from ...
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1answer
53 views

How do we see if light scatters in all directions?

This may be a silly question, but I'm not sure how we see an object in front of us. If light hits the points of the object and scatters in all directions, how come we are able to form an image of the ...
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2answers
64 views

How does a camera or eye detect violet if the smallest wavelength pixel element only detects blue?

Since cameras have RGB sensing elements per pixel, and eyes' cones similarly detect color with red, green and blue variants. The spectral sensitivities of the eyes are something like the following, ...
3
votes
1answer
89 views

Why farther objects do not look dimmer?

As far as I understand it, a light bulb irradiance (and illuminance) fall off following the inverse square law with distance, however radiance does not. I wondered why we (and cameras) do not see ...
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1answer
42 views

Speed of light dependent on source velocity in other medium [duplicate]

Does speed of light depends upon the velocity of source in a medium (like water) other than space? if yes, does the speed gets added up when the light source moves in direction of light?
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2answers
66 views

Spaceship A and Spaceship B move in opposite directions at half the speed of light, and A fires a laser at B, does the laser light reach Spaceship B? [closed]

This question has been bugging me for a week now! I believe it would, but logically, I feel like I'm missing something. Please give a full explanation.
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0answers
28 views

How can compact fluoscent lamps light up?

My understanding of fluorescent tubes is that filament on one side gets very hot, undergoes thermoionisation and shoots electrons into the gas. The collision between a mercury gas atom and a fast ...