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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2
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1answer
29 views

Lux and W/m2 relationship?

I am reading a bit about solar energy, and for my own curiosity, I would really like to know the insolation on my balcony. That could tell me how much a solar panel could produce. Now, I don't have ...
4
votes
1answer
343 views

Why Do My Fan Blades Produce Color When They Spin?

I've posted a short video on my Dropbox as a visual aid. Whenever I put my fan on Medium speed during the night time, it produces a rotating Blue and Orange color design, despite both fan blades ...
0
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1answer
49 views

Why do we perceive a colour?

White/yellow light hits a red case, and the red color is reflected into our eyes, since other wavelengths are absorbed. My question is: since both the paint on the case and the white light have ...
1
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0answers
31 views

What causes the lines in these photos of a flourescent tube?

I was taking pictures of a flourescent tube using a Moto G 2013 when I noticed these evenly spaced lines as I got closer to it. The distance between the lines reduced as I got closer to the tube. ...
-1
votes
1answer
36 views

Can quanta have different energy levels? [on hold]

The energy of a wave is h*f. How i imagine this is each cycle consisting of 1 quanta. I sometimes hear people say the energy of a photon is equal to h*f which makes it sound like each cycle has a ...
0
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2answers
21 views

Why Can You Only See Direct Light In Water From a Lighthouse

Whilst observing a lighthouse, I noticed that I could only see the cone of light reflected in the water when the lighthouse light was directly pointed at me. At all other points, I could just about ...
0
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1answer
29 views

Is scattering cross section determined by mass?

This is just for visible light/photon scattering. Let's say I have small spherical particles in water, if I keep the weight concentration of glass the same but change the diameter of glass sphere from ...
0
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2answers
58 views

Light-Matter Interaction and Object's Appearance

I am taking a course in Computer Graphics, and the teacher said we could put materials in there main categories: mirror like glossy or specular diffuse He suggested that the law of reflection is ...
7
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2answers
453 views

Frequency modulation using visible light

Currently I am doing research into visible light communication from an Embedded Systems background (MSc), but I am struggling to relate the concepts of modulation of radio to visible light. I already ...
1
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1answer
55 views

Police laser speed detection guns

Situation Police shooting a laser device into his rearview mirror, bouncing off the oncoming car license plate. I want to know if this second surface mirror, and the symmetric system--laser gun to ...
0
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4answers
43 views

Can the term «shadow» pertain to anything else than light? [closed]

Can the term shadow pertain to anything else than light? Feel free to interpret this question in the widest sense possible.
2
votes
1answer
70 views

A mirror in the sky to look at past Earth

Earth reflects light from Sun into Space; are there any "mirror like" objects which reflect back to Earth this light? Has anyone been able to use this method to recover some information on how was the ...
4
votes
3answers
357 views

Why does Snell's law not factor in wavelength?

If dispersion is caused due to different wavelengths bending with different angles, how is Snell's law right in generalizing it as $\sin(i) / \sin(r)$? Or am I missing something?
1
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1answer
71 views

Do photons change velocity instantaneously?

Any object traveling at c is observed as traveling at c in all reference frames. When a photon travels through a vacuum at c, all reference frames observe it traveling at c. When a photon passes ...
0
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1answer
31 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
4
votes
1answer
48 views

Why is it hard to make black clothes?

I've noticed that we have so-called 'black' clothes everywhere, I haven't seen so far any piece of clothes that would be really black, it's always some kind of lighter black. For instance, if you ...
4
votes
2answers
89 views

A light so strong it has a shadow

I have recently taken an interest in shadows. I know that in order for a shadow to exist that you must have a solid in the way of the light. My hypothesis is that there can be a light so strong, like ...
0
votes
1answer
43 views

If sound travels through matter what medium does light travel through? [duplicate]

So sound is a wave and is basically just vibrations, an atom vibrates causing another next to it vibrate and so on until it finally reaches our ears to become sound. If that's normally how waves ...
1
vote
0answers
57 views

What is light and how does it travel? [duplicate]

My question is: What is light, and, more specifically, how does it travel? I've been contemplating a theory that I watched on Youtube (which has no real credibility to my knowledge), the Cosmic ...
2
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1answer
466 views

Dark matter a medium for light propagation

Is dark matter a candidate to fill void left by luminiferous ether as a medium for light travel?
4
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1answer
467 views

What is the meaning of this “let there be light” joke?

A middle school teacher across the restaurant is wearing this shirt, and I certainly don't get it.
0
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2answers
91 views

Energy & Mass of a Photon [duplicate]

$$\text{Please read the whole question before answering}$$ Before I ask my question, I would like to say that "Yes, I do know a photon has no mass." I was helping someone here on P.SE with the ...
1
vote
1answer
48 views

What happens to light at sharp points? [closed]

At the tip of the sharp point shown, what will happen to light incident on it. This curiosity was invoked by a friend and also my childhood of watching shiny pointed swords in cartoons. Original ...
1
vote
1answer
49 views

Photons “rate of fire”

I'm not sure if this makes any sense but, do photons "discharge" from a source at an infinite rate?
4
votes
2answers
192 views

If atoms have specific energy levels, why do opaque solids absorb all visible light, not just some? [duplicate]

Here's my question: if atoms have well defined energy levels and those differences correspond to the frequencies of light that can be absorbed, how is it that opaque objects absorb all or most visible ...
2
votes
4answers
113 views

Photons to Represent a Wave

I fear that I have a fundamental misconception about the "wave particle duality" of light, but in a related question, the answerer said, in some sense, that a light wave propagates until it hits ...
2
votes
1answer
96 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
votes
1answer
78 views

Making fire using a filled water bottle

I have seen videos where a fire was started using a water bottle filled with water. I guess the bottle acts like a convex lens that converges light to a focal point to start a fire. But why does water ...
0
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0answers
33 views

How does light travel at the speed of light? [duplicate]

If it is impossible for matter to accelerate to $c$ (because doing so would take infinite energy), and if light can be deemed matter (because of wave-particle duality, photons are matter, right? And ...
1
vote
1answer
36 views

Can a single photon be polarized non-linearly?

I want to check if I correctly understand polarization. Considering a single photon travelling in vacuum, it can only be polarized linearly under the same direction at any time, right? When we talk ...
0
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2answers
35 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 distance s ...
4
votes
2answers
83 views

Why slightly closing your eyes let you see the rainbow colors?

So I was sitting and looked at a street lamp outside my house. It is an ordinary lamp that looks something like that: This lamp emits white light and it is about 20 meters from my house. It was ...
2
votes
4answers
85 views

Why wire filament shakes inside a light bulb?

My light bulb cast a clear light toward adjacent wall and I can clearly see, that wire filament inside bulb shakes, though lamp itself does not moves even an inch What is causing this? Is it a ...
2
votes
0answers
47 views

Deformation of light-cone

In the paper The geometry of free fall and light propagation by Ehlers and his colleagues (Gen. Relativ. Gravit. 44 no. 6, pp. 1587–1609 (2012)), when the authors introduce the differentiable ...
0
votes
1answer
48 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, ...
26
votes
6answers
6k views

Can you run away from your shadow?

Now this might be a silly question but it's actually bugging me, this one might be easier to understand if you have kids that watch (or used to watch) Peppa Pig. In one of the episodes, about shadows, ...
9
votes
2answers
166 views

Which of these theories on why light slows in media are true?

This question is similar to previously asked questions, but the responses to them are confusing and I think it may be better covered by listing out all the potential answers for clarity. It's a ...
8
votes
2answers
124 views

Why does the sky suddenly look gray through this window?

I am looking to the windowed roof of my building, and I notice that the sky, which has few white clouds, sometimes looks completely gray, as if there was a huge cover of gray clouds, but there are ...
0
votes
1answer
23 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?
1
vote
0answers
32 views

Is there any acceleration of light? [duplicate]

I find it hard to believe that photons always travel with 3 x 10^8 m/s just from the start. But there must be some acceleration of light. Maybe huge or taking place in picoseconds. So what maybe the ...
3
votes
3answers
212 views

Light has a wave particle duality, how do we know?

I've been told my whole life that light is either a wave or a particle. When it's traveling through space, it's a wave. When it hits a wall, or a photo-sensitive chemical strip or something similar, ...
6
votes
3answers
658 views

Why can't light penetrate solid objects?

Light is combination of perpendicular electric and magnetic fields, since electric fields penetrate a conductor, why can't light travel in them? I think my argument does sound stupid, but I can't ...
1
vote
1answer
49 views

Redshift of a reflected photon from a solar sail

Can someone help me understand my mistake here? I'm thinking of a photon travelling with momentum $p=h/\lambda$ which reflects off a solar sail of mass $m$ travelling with momentum $p_0$ in the same ...
1
vote
1answer
23 views

Relation between intensity of light and refractive index

The intensity of light (as calculated from time average of the poynting vector) is given by $I = (1/2) \epsilon v E_0^2$. Here the intensity is dependent on the velocity of light in the medium. The ...
4
votes
2answers
71 views

What is the physical structure of light?

Conceptually, I understand what light is, but I don't know what a photon would "look like" if it could be frozen in space/time. For instance, the notion of amplitude seems to be absent when discussing ...
-1
votes
1answer
80 views

Does the formula $ \theta = \frac{v}{c} $ to find out deflection of light make sense?

I read in reliable sites that GR and classical physics calculate the angle of deflection in the same manner. The formula is almost identical: $$\theta = \frac{4GM}{c^2*r} \rightarrow \frac{4GM}{c*r} = ...
25
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2answers
3k views

Why is the sun brighter in Australia compared to parts of Asia?

Background: I've lived in Philippines for several years, and visited other parts of Asia occasionally (Singapore, Indonesia, Hongkong). I just moved to Western Australia a few months ago and I ...
2
votes
1answer
36 views

Optical fibre modes and intensity pattern

I shine laser line in front of one side of multimode optical fibre.Light coming out of other side is projected into wall.Whether the intensity pattern seen on wall is same as the mode of propagation ...
0
votes
0answers
30 views

Cause and properties of northern lights [duplicate]

If outside on a dark night in the middle to high latitudes, one might be able to see an aurora. It may be several hundred kilometers high and several thousand kilometers long, stretching around Earth ...
2
votes
2answers
101 views

How can heat turn into light

I am confused about how hot surfaces can radiate light to their surroundings. When I shine a light on a surface the light turns to heat spontaneously, and when I leave that hot surface it radiates ...