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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2answers
202 views

Is a white object always white?

Is a object that’s white with the lights on, still white although it looks different under a different light or in total darkness?
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0answers
47 views

How can spacetime affect massless entities? [duplicate]

Why is light affected and "bent" by spacetime if it has no mass or density?
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1answer
650 views

Why do objects of a given color appear white under light of that color?

Under light from the sun, a red object will scatter the red component of light, and absorb all others. Hence, the human eye perceives it as "red". White objects scatter all wavelengths of light. ...
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2answers
1k 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 ...
0
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1answer
320 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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3answers
277 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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5answers
688 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
3k 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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5answers
1k 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
1k 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
32 views

Predicting solar storms?

Quote from BBC "A strong solar storm is expected to hit Earth shortly, and experts warn it could disrupt power grids, satellite navigation and plane routes." How is it that we are aware of a massive ...
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2answers
463 views

Blue-shifting as opposed to violet-shifting

A recent XKCD comic implies that the sky is blue as opposed to violet due to human physiology, and that animals more sensitive to shorter wavelengths will perceive the Earth's sky as the shortest ...
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2answers
393 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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3answers
8k 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
1k views

Can spectacles converge sunlight to an extent that it burns the eyeball?

I need to know whether wearing spectacles can cause optical harm. I saw a movie where one pair of glasses was placed on table exposed to sunlight, then the sunlight converged and focused to a point ...
5
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2answers
647 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
148 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 ...
5
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1answer
127 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
3k 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 ...
5
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1answer
938 views

What is the colour of starlight?

I'm interested to know the colour of starlight - particularly in rgb terms, I'm pressuming it's either white, or very close to white, but I'm interested to know how close. To make it slightly more ...
5
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1answer
192 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
12k 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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2answers
141 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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1answer
115 views

Is it possible to apply force to a light particle?

I know, the universal speed limit is the speed of light $c$. So, is it possible to apply more force to a light particle? What would happen to it if we could?
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3answers
391 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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1answer
169 views

Why are reflected objects blurry?

While this may seems like a strange question, I'll try to explain it the best I can. Like 75% of Americans, I wear glasses and contacts to correct my worsening vision. I'm not far sighted so objects ...
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4answers
121 views

Coherence effect on collecting sun light by mirrors

There are systems that collect sun light in one spot. I wonder, why does it accumulate additively, without destructive interference?
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3answers
355 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 ...
3
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1answer
577 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
757 views

What “exactly” happens when a ray is incident at the critical angle?

The question arose when my physics teacher taught me geometrical optics and told that the phenomenon of both refraction and $reflection$ occur by change in medium. First of all, I'm not sure about the ...
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3answers
1k 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 ...
2
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1answer
162 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 ...
2
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2answers
763 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 ...
2
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1answer
329 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 ...
2
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2answers
184 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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3answers
223 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 ...
2
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1answer
104 views

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

This has started to bug me more and more… it involves: colour theory the trichromatic properties of our eyes through cone cells and light. Is there a one-to-one relationship between colour ...
2
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1answer
289 views

What's the difference between the equivalence principle and curvature of spacetime?

Calculating using the equivalence principle only accounts for half the deflection of light, whereas the other half is from curvature of space-time. But isn't the equivalence principle the same thing ...
2
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2answers
572 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 ...
2
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1answer
631 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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2answers
210 views

Light, being a probability wave, carries energy; does an electron wave also carry energy? If so, how?

The entity "light" behaves as a wave & particle. The wave is actually probability wave . That is, to every point in a light wave we can attach a numerical probability that a photon can be ...
1
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2answers
464 views

Why does a circle of light appear when I shine a laser pointer at a wire? [duplicate]

When I point a laser at a wire , a circle of light appears on a wall behind it . why this happens. What is the circle of light and why does it appear? Could anyone give some tips on what I should ...
1
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4answers
274 views

Double rainbows

In my garden, when I'm watering the plants I sometimes see a rainbow or two. How did two rainbows appear? Why can't I see three rainbows then, or how can I see three rainbows?
1
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1answer
658 views

Visible light through a single-mode optical fiber?

If I understand things correctly, the optical fibers used for (long-range) data transmissions are generally single-mode fibers, transmitting light in the 1300-1500 nm spectrum. Now, could such a ...
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2answers
1k 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
130 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
57 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
300 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 ...