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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Photons and Black holes

How many photons in one Planck volume would it take to form a tiny black hole? A photon doesn't have mass but it does have energy, $1.0101 \times 10^{-37}$ Joule for red $650$ nm wavelength light if ...
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2answers
842 views

Is there 100% reflective mirror…i just want one

I have heard there are none right now...but i saw something that said something about 100% reflection. Forgotten completely. sorry. I want it, i think it'd be very amazing to save sunlight in it from ...
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3answers
249 views

Does the Lorentz transformation not apply to light?

Since you would know that light always travels at the constant velocity with respect to all frame of reference ....according to relativity whenever we are traveling at speed of light our time with ...
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1answer
210 views

Can light exist without spacetime?

Since the medium in which light propagates is spacetime, would light be able to exist if spacetime did not exist? Is this like one of those chicken/egg problems, or can light be thought of as a ...
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5answers
451 views

Is velocity of light constant? [duplicate]

There is a difference between the concept of the speed of light and the velocity of light. are both of them constant ($dc=0$ and $dv_c=0$)? if yes, why?.
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5answers
2k views

What do the colors in false color images represent?

Every kid who first looks into a telescope is shocked to see that everything's black and white. The pretty colors, like those in this picture of the Sleeping Beauty Galaxy (M64), are missing: The ...
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2answers
2k views

Has everything we see happened in the past?

Whatever we see is basically based on the light that hits our eyes, right? When we look at the Moon we are looking at the Moon as it was couple of seconds ago, as the light takes some seconds (~2 ...
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6answers
9k views

Is “dark clothes for winter, light for summer” relevant?

We are told to wear light clothes in summer as they are better at reflecting sunshine and keeping us cool. And dark clothes absorb sunshine and keep us warm. But is it really relavent? If I buy ...
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5answers
945 views

Superposition of electromagnetic waves

The superposition of two waves is given by $$\sin(\omega_1 t)+\sin(\omega_2 t)=2\cos\left(\frac{\omega_1-\omega_2}{2}t\right)\sin\left(\frac{\omega_1+\omega_2}{2}t\right).$$ For sound waves, this ...
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2answers
1k views

What does the sky look like to human eyes from orbit?

There are numerous pictures, obviously, of the blackness of space from the shuttle, the space station, and even the moon. But they all suffer from being from the perspective of a camera, which is not ...
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2answers
925 views

Slowing down light in an opaque crystal for a whole minute

I just read about a team of physicists at the University of Darmstadt, Germany, that managed to completely slow down a beam of light that traveled through an opaque crystal (article here). How is it ...
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2answers
385 views

What is changing in latest light bulb technologies?

I'm confused with the latest home lightning bulbs. Understanding filament bulbs was easy. For example take 220V, 100W filament bulb: Power = $V^2/R$ Filament gets heated and emits energy in the form ...
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2answers
252 views

Squinting at light sources

I am sure it's just your eyelashes creating a filtering effects, but if you look a a bright(ish) light source such as a lightbulb while squinting, if looks like you are seeing straight light rays ...
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2answers
103 views

Redshifting of light from a moving light source

We know that the expansion of space causes redshifting of light. I even read somewhere that the Doppler effect also happens in light. So imagine I switch on the headlights of my car in front of a ...
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1answer
102 views

Predominant light frequency over the day?

I'm not well-versed in physics, so I hope you'll forgive me if this question is significantly off the mark. I'm interested in the predominant frequencies of light over the course of one day. My ...
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2answers
2k views

How photons represent colors that you see?

Right now, my understanding is that, a mixture of photons of many different frequencies is perceived as white by your eye. While no photons at all, is perceived as black. And photons with the blue ...
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1answer
183 views

What would a length contracted object look like?

I have multiple sub-questions but they are related. What would the object look like if in were passing by? What would a star look like if we were traveling near $c$? Would the perspective be a a ...
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2answers
9k views

Why does earth look blue from outer space?

I know it's more than 70% water. But what has it got to do with earth's colour ?
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3answers
6k views

What invisible flicker do different types of light bulbs have?

What waveform does the light coming off different types of artificial light sources have and (of course) what are the underlying physical reason for them? I was inspired to ask this question ...
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2answers
106 views

Is ocean color affected by Rayleigh Scattering?

We know that sky color is due primarily to Rayleigh scattering. Is Rayleigh scattering the dominant effect for ocean color too?
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3answers
297 views

Making a plastic scintillator glow?

I have a plastic scintillator I had purchased off eBay, which is believed to be BC408 http://www.phys.ufl.edu/courses/phy4803L/group_I/muon/bicron_bc400-416.pdf Upon shining a small UV LED (10-40mA, ...
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3answers
247 views

What electric field vector should I use for modeling unpolarized light?

Regardless of computational cost, light is a kind of electromagnetic wave, so it can be simulated with Maxwell's equations. If we want to simulate light with Maxwell's equations, we need to express ...
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4answers
5k views

Why is there a difference between additive and subtractive trichromatic color theories?

Helmholtz distinguished between additive and subtractive trichromatic color theories. Additive theories concern optical combinations of colored light sources and are usually modelled on RGB while ...
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4answers
3k views

Is it only red, green and blue that can make up any color through additive mixture?

I'm reading about color vision and have some trouble understanding the motivation for why the trichromatic theory was suggested in the first place. The book I'm reading ("Psychgology: The science of ...
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1answer
527 views

Formula for polarized “light” transmission through close filters?

I'm still trying to understand photons (or polarized electromagnetic radiation). This question is similar to one of my previous questions, but different: Consider the famous demonstration of crossed ...
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3answers
195 views

What happens to photons after they hit objects?

If I am not wrong when light hits for example white wall most of the photons are absorbed and transformed into heat and few of the photons at certain wavelength are reflected from the object. So white ...
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1answer
119 views

Is light so important in special relativity?

I'm an amateur physics enthusiast with no formal university education in Physics. So my question might sound very naive, so forgive me. I had this question in the back of my mind since the wrong ...
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2answers
245 views

Calculating the coherence length from a spectrum

I have measured the spectrum of the LED in my interferometry set-up, and now I want to calculate the coherence length from it. A commonly found formula is $l_{coh} = \frac{c}{\Delta f}$, sometimes ...
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1answer
189 views

Red color has largest wavelenght and violet minimum (in the range of visible light). then why does violet light appears reddish? RED + BLUE = VIOLET [duplicate]

My question is simple. Green light is more similar to red light than violet, then why is violet reddish and green not? in the language of frequencies and wavelengths, red and violet should contrast ...
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2answers
121 views

Does any material glow, under appropriate conditions?

Given a high enough temperature, or a high enough electrical field, can we make every material emit visible light?
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2answers
231 views

Can we observe diffraction even if the slit size is tending to zero?

According to Huygens principle, if we consider any point of the primary wave fronts, each point is the source of secondary disturbance. If the point size we consider tends to zero, the number of ...
2
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1answer
99 views

Is there a one-to-one relationship between colour theories and our trichromatic vision?

This has started to bug me more and moreā€¦ it involves: colour theory the trichromatic properties of our eyes through cone cells and light. Is there a one-to-one relationship between colour ...
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2answers
492 views

Electron model under Maxwell's theory

I was not able to recall my memories, so: What is the formula that states the frequency of electrons revolving around nucleus is equal to the frequency of light (or photon) emitted (or radiated)? (I ...
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1answer
558 views

Snell's Law of Refraction

I was told that "Snell's law of refraction implies that a light ray in an isotropic medium travels from point a to point b in stationary time." Why is this true? Thanks.
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3answers
74 views

Relation between wavelength and system size

We always say that when a given light wave interacts with atoms bound in a molecule, only waves with wavelength close to the inter-atomic-spacing are able to probe the system. In other context ...
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3answers
159 views

How far does a Photon's field Extend?

I read the related answer to whether photons have size, and the answer seemed to be it depends. If a Photon, or a rather an E&M wave has a magnetic and electric field, should things be able to ...
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2answers
677 views

Why are two independent sources incoherent?

Coherent sources are produced from a single parent source. But, why are two independent sources always incoherent? Two sources can produce light of the same frequency. Then, I guess the problem is ...
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0answers
104 views

How to get “massless” equation of motion from the action of Nordstrom scalar field theory?

There is Nordstrom theory of the particle moving in a scalar field $\varphi (x)$: $$ S = -m\int e^{\varphi (x)}\sqrt{\eta_{\alpha \beta}\frac{dx^{\alpha}}{d \lambda}\frac{dx^{\beta}}{d ...
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0answers
51 views

Is there any evidence that everyone sees colours the same way? [duplicate]

We all know that the sky is blue. Grass is green. Blood is red. But, how do we know that everyone sees these colours more or less the same? How does one know that my ...
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1answer
233 views

Principle of relativity and motion perpendicular to the direction of light beam

consider you are in a train that moves with a speed of $c/4$. A bulb is hanged from the ceiling. A light beam leaves the bulb downward. Exactly under the bulb on the floor is a detector. According to ...
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2answers
446 views

Is there a way to see light frequencies invisible to the human eye without the use of electronic sensors?

I wonder if it's possible to be able to see light frequencies that cannot be normally seen by human eye, without using sensors designed specifically for detecting a certain spectrum range, but rather ...
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1answer
4k views

Could the shadow move with faster-than-light speed? [duplicate]

If I make a huge laser with a figure for shadow in front of the laser, and I shine it on to the moon, will I see the light from the laser AND the shadow moving the same speed? (I read somewhere the ...
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3answers
96 views

Trapping EM radiation [duplicate]

Is there a material which can allow light (or any other EM radiation) to pass through from one side as if it is transparent but its other side reflects light like a mirror?
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2answers
1k views

Reflectance vs. Thin Metal film Thickness Graph

Is there formula that gives reflectance of very thin film of given metal (tens of nanometers) to the visible light of given wavelength(808nm) ? Which properties of metals are needed for the formula ? ...
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1answer
365 views

How does a strobe lamp stop a fast moving object?

A strobe lamp can be used to seemingly stop a fast moving object when calibrated. Commonly used in quality assurance during production to inspect otherwise non-observable assembly line activity. What ...
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1answer
355 views

Combining Multiple Light Sources

Ok, Lets say I have two point light sources A and B. Each light source has a power Pa and Pb, and is distance Da and Db away from a point P on a plane. I can calculate the amount of luminosity at ...
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3answers
891 views

Conversion formula from spectrophotometer readings to any standard color space profile?

I have readings of colors from a spectrophotometer that records across the human visible color spectrum 390nm to 790nm intervals. I'd like to convert this into any color space, could be CIE XYZ, HSL, ...
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1answer
47 views

What happens to the energy of photons when two light waves with plane wavefront interferes destructively? [duplicate]

When I began learning about optical interference, I came to know about destructive interference in which light waves cancel each other. How the energy is still conserved ? I found that the ...
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3answers
122 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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0answers
55 views

Mathematical formalism to include wave and particle perspectives of light

Does the exist any mathematical formalism (model) describing the behavior of light and incorporating its particle character (divisibility, quantization) and wave character? (i.e. quantized wave model) ...