# Tagged Questions

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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### How does light behave after experiencing fully destructive interference, as in an interferometer?

I'm thinking about a laser interferometer like the one used in LIGO. Here's the basic layout (from Wikipedia - Interferometry): My understanding is that the half of the light that is reflected by ...
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### What is the term for the area of light produced by a source?

A light bulb is a certain size, yet the area that the light reaches is much larger, what is the name of that term?
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### How much light is necessary to form a black hole

I suppose that enough light in a small enough volume could create a black hole. What is the good quantity that can tell when light can or cannot make a black hole? Energy density? But there must be ...
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### What is a Light Efficient System?

When reading this paper, I encountered this sentence on the sixth page: When used in conjunction with wide-field microscopy, iterative restoration methods are light efficient. This is most ...
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### How to solve this problem : A glass sphere of radius 1 m and refractive index 1.5 is silvered…? [closed]

Problem: A glass sphere of radius 1 m and refractive index 1.5 is silvered at its back. A point object is kept at a distance of 1 m from the front face, as shown in the figure. Find the position of ...
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### Why do we see discrete light spikes coming out from a light source?

When we look at a light source from a distance in suitable darkness, why do we see discrete light spikes coming out of source like Fig. b of above picture instead of Fig. a?
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### Where are the electron exchanges happening in solar cell physics when considering the photon?

When considering solar panel physics, are we taking an electron from Light(photon), or is the energy of Light causing an electron to jump in said solar cells through excitation? Is the photon even ...
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### Light is/produces a electromagnetic wave, but is the opposite also true?

A similar question has been asked, and to some extent the answer is: you need an antenna with $L \approx 200nm$. But it's not entirely clear to me if this is completely hypothetical, as "Marek" also ...
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### illuminance on a slope plane

I am trying to understand the illuminance from an extended source(sky dome) on an inclined plane. The article I am reading has beautifully explained it. Yet I don't understand the angles and boundary ...
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### Why is reflected light polarised?

Why is reflected light polarised? I have learnt about Brewster's angle, and how at a particular angle all light reflected is polarised, but do not understand why. Is this something that could be ...
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### DIY optical band pass filter or another alternative

I need to detect laser using a solar cell which would need me to either detect the laser wavelength or use pulse modulation and detect the frequency so I'm kinda here to ask if it's possible to simply ...
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### optoelectronics-smallest wavelength of light

Sorry this maybe a stupid question , but i need to know: A few minutes ago i have read an article about optoelectronics: worlds first optical single atom switch The writer of the article claims:"...
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### Will I see the light?

There is a perfectly smooth wall. We have a slit parallel to it. Through that a laser beam passes. As the slit is parallel to wall the laser beam will hit it normally. So now if I see obliquely I ...
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### Bending of light [closed]

Why does bending of light(diffraction) occur?
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### Blue light filtering

Prologue: my knowledge in these topics is fairly limited, so please feel free to point out the mistakes or the not-so-clear points, and bear with me for the oversimplicity of the language used. I was ...
186 views

### Why does a laser beam stay collimated?

I am looking for a simple way of explaining the collimation of a laser beam. The typical discussion of the two slit experiment of quantum theory relies heavily on the Huygens principle. Its ...
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### How physicists explained straight line propagation of Light thinking of light as wave? [duplicate]

To explain the fact that light travels in a straight line assuming light as a wave physicist said that it has small wavelength. So how does the small wavelength explains the property?
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### A Neutron Star and an Atom are Similar [closed]

In an earlier question I asked if photons could exist without atoms. Is a neutron star's residual light released similar to an exited atom the difference is gravity hold in the electrons in the star ...
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### Where else than Atoms do Photons Disappear and Reappear from? [closed]

Where does photons come from and disappear to? Can photons be destroyed and created? Without atoms would photons exist? What other ways then from atoms can photons be made?
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### How can light appear to spread in mainly a few rays (e.g: 2,4)? [duplicate]

I think it's easier to explain the question with some images. Here you can see a six-rayed one: I cannot post more than 2 links, so: www.i.stack.imgur.com/23YLa.jpg www.i.stack.imgur.com/4WqEU....
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### When i look to a lamp at night, from a distance what happens?

Lets say its night, and i look at a lamp 20 meters away from me. Im obviously in the darkness, but i can see the light from the lamp, if the photons need to stimulate my eyes in order for me to see, ...
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### Is illuminance defined only on a surface normal to the flux?

Assuming on the below image the source is a point source, I can understand that since the light flux falls on dA is the same within the solid angle and since the intensity I = Φ/dω and E = Φ/dA it can ...
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### Implication of Relativity [duplicate]

According to relativity, no useful matter can travel faster than light. Suppose that your are a light beam travelling. Now you have a parallel light beam travelling beside you. Suppose you look at the ...
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### How we are able to see red and green colored objects simultaneously if combination of red and green produces yellow?

If red and green cones in our eyes are tiggered simultaneously then our brain makes us see yellow color. But if two objects which have red and green colors respectively are placed infront of us then ...
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### Why does Diffracted Light cone diameter change in relation to angle of light beam?

I have a question about light diffraction. Take a look at these images of the Pantheon oculus. Now what I don't understand, in the first picture, the light is coming in from overhead and forms a ...
272 views

### How to calculate a straight edge diffraction pattern

A straight edge diffraction pattern is not the same as a slit or multiple slit diffraction pattern. The spacing between fringes is not equal but gradually gets smaller the farther out you go as in the ...
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### Impossible? Or not? [closed]

If the universe is expanding at light speed, and you stand on the edge moving out, if you look across the universe, then you will see twice the light speed, why is that?
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### Linear polarized 3D glasses and the physical shape of light waves

Looking into how linear polarized 3D glasses work, I keep getting explanations that boil down to this: However, I always assumed that a light wave was depicted in diagrams like this... ...to more ...
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### Field of view from travelling at (almost) the speed of light?

As we go faster, our field of view increases, but would happen if we travelled at (almost) the speed of light? My questions: Can we see a 360 degree view while travelling at (almost) the speed of ...
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### How do we call in English scientific terms the Fermat's principle about back and forth light traversal?

We know that the path followed by the light from point A to point B is independent of the direction of propagation of light. This is what is called in French "le principe de retour inverse de la ...
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### Telescopes and faster than light travel [closed]

If sometime in the future we master faster than light travel, could we solve past crimes by warping to a place in space where the light from Earth is just arriving from that time period and using a ...
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### What would happen if a monochromatic light falls on an electron?

An electron is not strictly free, but in terms of QFT, we consider scattering events in an asymptotic framework where free particles would arise at $t \rightarrow \pm \infty$. So, I would like to know ...
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### Gravitational Lensing Example

Like this tomato wrapped underwater and how light is bent around it does the way a black whole bends space and light in the same way?
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### Same amount of light, spread across larger surface area = more reflection?

I've noticed an odd phenomenon with an adjustable-focus LED flashlight that I've bought. If I shine it at the ceiling of my room at the widest possible angle, the walls get noticeably brighter than ...
253 views

### Why should angle of incidence be equal to angle of emergence for minimum deviation in a triangular prism?

When I was solving questions on Ray optics I encountered a question wherein I had to prove that when a ray of light undergoes minimum deviation through a triangular prism then both the angles of ...
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### Can we have a microscopic image of light itself?

Is there a way we can see light in a microscopic scale- alaser beam to its depth? Possibly seeing the structure of photons.
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### Wavelength limited resolution

I've read through answers to similar questions, and I haven't been able to find a satisfying answer. I've heard it said that in order to make out something, you need to use light with a wavelength at ...
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### Constancy of speed of light in vacuum? [closed]

Have scientists tried their best to calculate speed of light in vacuum? It seems very absurd to me that light of all frequencies have same velocity in space. Can someone find in future if this speed ...
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### What would happen if light was stored in a circular path? [closed]

This is like an idea for experiment. Lets say one has an optical cable that makes a circle. There is a little Y junction/valve to the circle, through which one pumps some coherent light in. The ...
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### What determines a colour of light? [duplicate]

Let's consider an air-glass interface. When light passes from the air to the glass its frequency stays the same, but the velocity and wavelength change. Now the problem starts. If the colour stays the ...
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### acceleration and its effect on the speed of light

One of Einstein's thought experiments involved a rocket and two light sensors inside the rocket, one at the top, and one at the bottom. When the rocket was at rest, a pulse of light from the bottom ...
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### Can light be rotated using lenses or prisms?

I was wondering if it was possible, by using only lenses, mirrors, or prisms, to rotate a ray of light coming from a certain direction. For example, if I have two lasers beams side by side, is it ...
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### Can I emit light from an inductor? [duplicate]

As I understand it, inductors create a magnetic field when current flows through them, and light is an electromagnetic radiation. So, is it possible for an inductor to generate magnetic waves of the ...
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### What happens to scattered light when intensity of light increases?

Does increasing the intensity of the incident light increase the proportion of the light that is scattered?
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### What happens to the group and phase velocity of light as it travels through a medium?

We have all been told that when light travels from, say, a vacuum through water it slows down. What I want to know is what happens to its phase velocity and group velocity. Refractive index is \$n = \...
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### Why are red colored object red?

I've read that all electrons want to be in their ground state, so when light from a source is absorbed by the electrons in a red colored object and forced the electrons into higher orbital/energy ...
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### Is it possible to get a lasing from every luminescent media?

Let's assume that there is a cavity with a couple of mirrors and gain media between which possesses luminescence under some external excitation/pumping. Let the absolute quantum yield of the gain ...
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### How does the sun rise upwards with brightening and set downwards with low fading being stationary on a spinning earth? [closed]

Can someone please apprise me with this phenomena that earth is spinning on it's own axis with 23.5 degrees tilt also rotating around the sun while sun is stationary. when sun is just rising up we can ...
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### Interpreting LED output distribution specification

I have specifications for an LED which gives the following graph of spacial output distribution. I am not sure how to interpret this. As I see it, it could be one of two ways. To make ...
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### Why do we see just one octave of light? [closed]

When one takes a look at the usual chart of EM spectrum one cannot help but notice that visible spectrum is slightly below one octave of frequencies; that is, the ratio between the highest and least ...