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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What is causing the separation of light in this image?

Reflection of keychain LED light on Macbook Pro (2014) screen I have also observed this phenomenon on my mobile phone and on a tablet. I assume this means it is somehow related to backlit ...
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33 views

Does general relativity have an effect of the frequency of light? [closed]

if a lightbeam is fired from space to earth is it blueshifted? I heard this happens with special relativity but not sure if it happens with genreal relativity
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2answers
83 views

Resolution of the Eye-Light Rays and Diffraction

Please look at the problem. The problem is solved for me. However, I don't understand why the angle alpha is considered to stay constant when the rays go through the lens. The ray along the ...
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1answer
91 views

Why do we observe opposite motion of trees (nearer) and trees (distant) when seen from a moving frame? [duplicate]

If you are in a moving train or in a bus, what you observe is that the trees which are nearer to you move opposite to the direction of your motion. But the trees which are very far away from you, ...
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40 views

Dissipating light pollution

If all the lights in a city, and the area surrounding it were shut off. How long would it take for the light pollution to clear, so the light from stars could be seen?
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3answers
233 views

How to generate Red light from a Blue-Dominated Spectrum [closed]

I have a white LED light source, the spectrum of which looks as follows --- I want to filter out red light from this white LED source. But as you can see the spectrum dwindles in the red zone. And ...
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1answer
117 views

Single slit diffraction pattern in 2D

I was looking at previous exams and I saw a question with single slit diffraction. Please look at picture on the website: http://www.physicsforums.com/showthread.php?p=4807732#post4807732 So, this ...
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72 views

Idea is to make an equipment like torch, which should emit darkness.. Is it possible? [duplicate]

Can we have any equipment as such? If light can emit form a hand held device, why not darkness
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443 views

Problem with plane mirror focal length thoery: Is the focal length actually infinite?

We all learned that the focal length of plane mirrors is considered to be infinite, as the radius of curvature is infinite. However, imagine this scenario: You have a perfectly flat (no one get mad, ...
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31 views

scattering of light

How does the path of light become visible due to scaterring of light? According to me it will only tell the presence of colloidal particle but the book give the example of cinema hall projector and ...
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49 views

Calculating the distance between Detector and Double Slit

I have a little problem that is kind of confusing me at the moment. The following task: Light of the wavelength $\lambda = 500nm$ hits a double slit whose distance is $a = 30\mu m$. Each is $a = ...
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1answer
114 views

Visual Fields testing: Decibels of sensitivity - meaning

Automated Visual Field test measures the patient light sensitivity in decibels. Questions: If one point has sensitivity of 30 decibels and another point has sensitivity of 27 decibels does it mean ...
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60 views

Why do the RGB gamut vertexes not intersect the edges of human vision on the CIExy plot?

As I understand, the CIExy graphic maps "greenness", or rather middle-wavelengthness, to the Y axis and "redness", or rather long-wavelengtsness, to the X axis. The trapping used to reduce the 3d ...
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31 views

Relationship between diffused light and intensity

I was wondering if the relationship of the intensity of diffused light is a linear correlation to the diffusing material. Basically will the intensity of the diffused light change in a linear fashion ...
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1answer
64 views

Does firing electrons at an object change its colour?

If one had an electron gun capable of firing electrons with a specific energy at an object, can it change its colour? I think it is possible because the emission spectrum of the material would ...
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1answer
62 views

Resampling spectral data?

I want to use the CIE CMFs (Color Matching Functions) provided here: http://www.cvrl.org/cmfs.htm With data from my spectrometer in 10 nm increments. However, the CMFs are only provided at 5 nm ...
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1answer
164 views

Implications of Formula for Stellar Aberration

I am studying relativity and was working on deriving stellar aberration using relativity. My derivation is as follows: Suppose that the observer is traveling at a velocity $v$ in the $x$-direction. ...
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233 views

Difference between mirror reflected light rays and rays of a screen

What is the difference between the light rays reflected from a mirror and rays directly emmited from a screen if the screen shows the same image as the mirror would.
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40 views

Diffraction from interatomic spacing

In diffraction from a single slit, we learn that the angular width of the central maxima, is given by $2\sin^{-1}\frac \lambda d$. For $d\approx \lambda$, the incoming wavefront should be spread to ...
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1answer
105 views

Young's DS experiment and most light sources

The reason why two independent bulbs cannot be used to create the young's two slit interference pattern is that the phase difference between those two sources varies very rapidly and therefore, the ...
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2answers
118 views

What is the transmittance function of a photo filter?

The effect of some photo filters can be summarized in transmission curves such as this one: I do not understand which physical value is modified by the value labeled as "Diffuse Density" in the ...
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2answers
115 views

Length of solid part of object shadow

Little background first: I take part in preparing environmental reports for wind turbines/farms and now I'm exploring shadow flickering effect of moving blades. From some sources (in Polish) I got ...
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1answer
80 views

is redshift still true if object emitting is not moving away but the observer is

If something is moving away fast it's color would appear redder than its actual color due to phenomenon known as Doppler effect. But what if the object isn't moving but i am moving away faster would ...
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111 views

Depolarisation of Light in Optical Fibre

I have a question for which I can't seem to find a solid answer in literature and wondered if anyone could offer advice or reliable references please: How does light depolarise in ...
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2answers
96 views

The speed of light through space and its effects on black holes

I was curious about a couple of things that don't quite make sense to me: (and probably won't when I get the technical answer, but I'll ask it anywise.) When light travels through space, is its ...
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1answer
91 views

Can Quantum Stealth be Real?

I've recently heard about this new material called Quantum Stealth which is suppost to be a replicate of Harry Potter's 'Invisibilty cloak' . Apparently the material, bends light waves around a target ...
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106 views

Light-Particle Wave Duality

There is a lot of reading to do on this to fully understand it, but without doing that reading is there a short explanation as to why and how light behaves as a wave and a particle?
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979 views

Paraxial rays and marginal rays question

Paraxial rays are found to focus far away the lens whereas marginal rays focus near to the lens, why? I didn't find satisfactory answer in my academic book..
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2k views

Young's Double Slit experiment question

Q-A beam of light consisting of two wavelenghts 600 nm and 450 nm is used to obtain interference in Young's Double Slit experiment (YDSE). Find the least distance from the central maximum where the ...
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1answer
357 views

What is the momentum of these emitted photons?

5 x 10^7 kg of radioactive material emits energy in the form of photons of red light (700 nm). (Note: photons have no mass.) What is the momentum of each photon? ...
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1answer
66 views

Regarding “Holes” in bands, and Photons

So from learning Band theory, and PN Junction and such, I've learned that photons are created when "holes" are filled in a band, and this is what can create light (Isn't this how LEDs work?) Anyways, ...
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1answer
458 views

Dispersion & Absorption in Optics

1) I understand light dispersion. But, I wonder what happens if I used a lens to focus it into a small point. Would it be a white point (would it reverse dispersion) or would I have a multicolored ...
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1answer
84 views

Is synchrotron radiation considered incandescent?

Synchrotron radiation is produced via the acceleration of charged particles, much like incandescence. However, all information I've seen state that incandescent light is produced exclusively from the ...
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1answer
317 views

Transmission of Gaussian Beam Through Graded-Index Slab

The $ABCD$ matrix of a glass graded-index slab with refractive index $n(y)=n_0(1-\frac{1}{2}\alpha^{2}y^{2})$ and length $d$ is $A=\cos(\alpha d)$, $B=\frac{1}{\alpha}\sin(\alpha d)$, $C=-\alpha ...
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283 views

Dependance of temperature on color of metals

I asked this question because I supposedly did last year, Stanfor Klein which belongs to the Solar Energy Laboratory of the University of Wisconsin says that "the color of a car does not affect its ...
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1answer
137 views

Is the acceleration and deceleration of a wave instantanious?

When an light travels in free space, it has a velocity of propagation equal to the speed of light. However, then the light enters a medium with a refractive index of n, the velocity of propagation ...
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1answer
131 views

Does diffraction contribute to the Black Drop effect?

Two reasons are given to explain the black drop effect here, but I think I came up with a third. Consider a two-dimensional cross section of the situation just after second contact and just before ...
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1answer
64 views

What kind of light is needed to light up Venus?

Let's say I would want to light up Venus, such that we can see Venus all day long and not have to wait for a Venus Transit. What kind of light would I need for it? How powerful would it need to be?
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1answer
200 views

Exist some relationship between irradiance units and wavelenght of the incident sunlight?

Exist some relationship between irradiance units and wavelength of the incident sunlight? What about irradiance? I want to establish a relationship between wavelength and irradiance, because I would ...
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1answer
96 views

Any process or algorithm to estimate color sensitivities or color matching function of a RGB camera? [closed]

CIE defined color matching functions (CMF) for XYZ and thus RGB colors. But of course, each camera has its own color sensitivities for visible spectrum. Is there any way to estimate this function (or ...
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1answer
25 views

Interference of waves

Every thing has a dual nature. So if we take waves(consider light interference) as particles, exactly what happens during interference (both constructive and destructive)? Can you explain in easy ...
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0answers
25 views

Can other animals see black differently? [on hold]

I am not sure if this is the right place for this question, but this is a debate that has been going on between two colleagues for days and I need a resolution because it's driving me crazy. So any ...
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1answer
43 views

Has the knowlege of rainbows gained from snell's law ever been used in a practical way? [on hold]

So, I'm an AP physics 2 student at the moment, and I'm learning about Snell's law and refraction. Due to the changing speed of light (for these purposes; I am aware that C is constant) in water ...
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19 views

Why does the spectrum for deuterium show a weak line at H-alpha?

I was wondering why the spectrum for deuterium shows a weak line at H-alpha, the first line in the hydrogen spectrum.
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0answers
39 views

Does Gravity Act on Any and All Things in the Universe? [duplicate]

I'm studying physics, and the questions below popped up in my head. I learned that all objects on planet Earth fall due to the influence of gravity. A ball falls. A mug cup falls. A coin falls. ...
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2answers
113 views

Why is the spectrum of a blue flame the way it is?

In the spectrum of the blue part in a candle flame, there’s a violet emission at 432 nm due to excited CH* molecules (chemiluminescence). Why 432? Why not 400 or 500? There are emissions at 436, 475 ...
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1answer
10 views

Saturation point of incident Light on an object

Since the color of objects depends on the parts of the visible spectrum reflected out and the remaining is absorbed; is there any maximum limit to which the absorption can take place? In other words, ...
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0answers
12 views

Is the link between shadows a refraction of the light? [duplicate]

When two objects in the sunlight approach, if you look at their shadows, they form a link when they are really close, is that an example of refraction? If so, is it the same as the refraction we see ...
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0answers
21 views

Generation of electromagnetic waves [duplicate]

I came across this while searching about generation of electromagnetic waves-Does this mean that if I vary the electric current following through a conducting wire, it will radiate electromagnetic ...
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28 views

How is the formation of the first atoms related to the cosmic microwave background? [duplicate]

Common atoms formed when the universe finally got cool enough for electrons to bind with atomic nuclei around the year 380,000. From what I understand this shift in state from plasma to discrete atoms ...