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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Determining the path of a light ray

Let's consider a ray in the plane $xy$. Let the refractive index be defined in any point of the plane with the function $n(x,y)$. In time $t=0$ the ray is located in coordinates $(x_0, y_0)$ and its ...
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473 nm light through a single mode fiber designed to operate between 1500 and 1600 nm

Can we send light with 473 nm through a single mode fiber designed to operate between 1500 to 1600 nm spectrum? The radius of the fiber core is 4.25 micrometer, NA=0.12 and the single-mode cut-off is ...
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125 views

What would happen to a star if a Dyson sphere lined with mirrors reflected a significant portion of the stars light back to the star

I have looked for similar questions here on stack exchange. The closest example to this that I found is Could a Dyson sphere destroy a star. That question assumed less than perfect absorption of ...
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52 views

How fast would you have to go to claim you saw the red light as green due to the Doppler Effect?

Driving toward it, I suspect you would have to be going at relativistic speeds. Calculating this, it appears to be around 1/6 the speed of light when driving directly at it, but since you are on the ...
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50 views

Why does radiance remain constant along rays of light through empty space?

In Radiometry, radiance (L) is defined as flux density per unit area per unit solid angle. If we move further along a ray, away from a point, shouldn't the radiance decrease? I am unable to grasp an ...
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46 views

How can light experience a force [duplicate]

According to the second law of Newton f=ma only objects with mass can experience a force. But light can be bent by gravity and is not supposed to have a mass. How ...
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22 views

Polarized Filtering Frequency Shift?

A polarized filter is exposed to a unpolarized light source. The output of the filter should be of lower intensity, hence lower energy. Should not the filtered light be of a lower frequency to ...
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1answer
73 views

Why does the sky look blue rather than violet? [duplicate]

Sky looks blue because because our eyes are sensitive to blue colour. But when viewed through a camera why don't we see violet of the sky even though we can see violet colour of other pictures taken ...
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1answer
45 views

Can a magnifying glass work on EM radiation other than visible light?

A magnifying glass is a convex lens which allows us to bend visible light, thus the image of the object appears larger. My question is, can a magnifying glass work on the rest of the electromagnetic ...
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3answers
78 views

Can we see a rainbow on moon or any other celestial body?

We see rainbows after rainfall on earth... According to my understanding a rainbow is formed as a result of scattering of light....Then is it possible that we can be able to see a rainbow on the ...
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1answer
90 views

Understanding the behavior of light/photons inside a Laser

I am trying to establish a model inside my head of how light behaves but find it hard with all the seemingly contradicting information. For example, electrons inside a Laser are raised to a higher ...
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1answer
49 views

Digital colors: why RGB instead of RYG? [duplicate]

We know that Red, Yellow, Blue are primary colors. Any other color can be created by mixing these color. Graphical representation is below: But when I began to learn about computers, I noticed that ...
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40 views

What is the maximum of information in a beam of light?

If I look at the space I can see the Andromeda Galaxy as a small dot in the sky. If I look through a telescope, I can see the spiral shape. If the saw right through a huge telescope, I could see a ...
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3answers
68 views

Why stars are white? According to Rayleigh Scattering

According to Rayleigh Scattering, the red waves are capable of travelling a long distance, so that only we are seeing the Sun as reddish during Sunset and Sunrise. If this was true then all other ...
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19 views

Absortion of light by a plasma

Considering a plasma generated in a fixed volume by increasing the temperature of Helium gas from the environment temperature (this temperature is not stated) and an initial presure of 0.001 Torr, to ...
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What is angular accelerating light?

As described in this article "Our angular accelerating fields rely on combinations of orbital angular momentum - so-called twisted light," says Forbes. Light carrying orbital angular momentum ...
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1answer
15 views

Recalculating lux from EV

I have to calculate amount of light from IR emmiter. The only equipement, that I can use is Sekonic Light Meter like this one: http://www.ebay.com/bhp/sekonic-l-358 The problem is that i need to have ...
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2answers
86 views

Theoretically, is it necessary that if light passes through a glass slab, its intensity should decrease?

Is it necessary that for an E/M wave of given frequency which can pass through a medium of given refractive index, it should lose some of its intensity. Practically, this must be necessary because of ...
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1answer
50 views

Polarization of light upon reflection

I was wondering (since I've looked pretty hard and haven't been able to find anything)- are there any models that explain the polarization of light upon reflection? Everywhere I've looked I've seen ...
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1answer
61 views

Difference between speed of light and of bullet after passing through a barrier [duplicate]

I just read that, when a ray of light traveling in vacuum at $c$ strikes a glass slab, its speed decreases and then when it re-emerges it gets back to its original speed i.e $c$. If I draw a ...
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1answer
47 views

Sound waves and chromism?

I am definitely not a physicist, but I have a question related to Physics so I thought I'd give it a try. Please excuse my ignorance. :) I am somewhat familiar with the changes in color caused by ...
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2answers
101 views

Why do we see light and isn't everything dark?

Suppose it is dark. If someone shines a flashlight directly at you, you see light. If, however, someone shines a flashlight at something else, you see that thing illuminated, but you don't see the ...
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54 views

What is the relationship between $a$ and $m$

$a$ is defined in HERE What is the relationship between the length-scale $a$ and the mass $m$?
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circular orbits in general relativity [duplicate]

I am studying the derivation of the circular orbits of particles in general relativity (Derivation) Question 1: What is the meaning of the constants $a$ and $b$, it says they are " length-scales", ...
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29 views

Conservation of Energy in Blue Shift

Imagine light coming down and hitting a neutron star. It light is blue-shifted. I know that energy/mass is conserved and that the energy to blue-shift it comes from the gravitational field, but how is ...
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1answer
160 views

A yellow lemon is illuminated by green light. What color does the lemon appear?

I think it's blue, but I'm not sure. Is there a way to find out without simply testing it?
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93 views

Find the electric field of light due to an LED [closed]

This is a JEE mains question which neither me, nor any of my teachers can figure out. Help me here. "A red LED emits light at 0.1 watt uniformly around it. The amplitude of the electric field of the ...
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77 views

UV filter, does it exist?

On the video here https://www.youtube.com/watch?v=o9BqrSAHbTc, Thomas Leveritt uses a UV filter which, as far as I understand, lets only the UV through. I couldn't find any photo filter that do that. ...
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83 views

What happens when both of Polarizing filter in LCD screen are Horizontal

What would be the result if we replace the vertical polarizing filter in LCD device (screen) with a horizontal filter, what could we see exactly? Would we see the same if we use only one horizontal ...
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27 views

How to combine contributions of individual type of cone cell sensitivity to get the human luminosity function?

As shown in this figure from some computer vision book: The data of three types of cone spectral responses is pulled down from: http://cvrl.ioo.ucl.ac.uk/cones.htm It is said that the Long, Medium ...
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1answer
58 views

What are the units of color matching functions?

In some computer vision book I read lately, the color matching function is invoked without clear definition of its units. I suspect the color matching functions are spectral irradiance or spectral ...
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1answer
41 views

Interference and windows

The other day i was learning about interference patterns with the effect of a bubble making a rainbow on the surface. I learned that the reflections from both sides of the soap can interfere ...
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2answers
134 views

Special Relativity - Distance Not Increased?

I just watched the movie Interstellar and the question was asked of why/how high-speed travel would slow time within an area. Curious as I am, I watched several YouTube videos to quickly 'educate' ...
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31 views

Path length requirement for diffraction problem [closed]

The following question has been asked in a problem sheet I have been asked to answer: "The above diagram relates to the path lengths of radiation, with an angle of incidence, θ, reflecting off ...
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2answers
44 views

Color of objects in Yellow sun

The sun appears yellow but the objects on the earth appear as if they have been illuminated in white light. Are all objects that we see in sunlight actually in a yellow shade, and would appear ...
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28 views

Florescents and radio waves

Okay so if you put a florescent light bulb in front of a certain radio, the radio waves excite the mercury inside a causes them to emit UV light which makes the outer coating of the light bulb light ...
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1answer
57 views

Surfaces that reflect UV rays

I've been trying to research what surfaces reflect UV rays for the past day but it's been difficult coming up with definitive answers. So far what I've found is that surfaces that reflect visible ...
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3answers
1k views

Why does red light travel faster than blue light?

I know that light of all frequencies travel at the same speed in vacuum. But I wonder why their speed differ in any other medium, why does red light travel faster if it has less energy than blue ...
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1answer
49 views

Polarization vector identity in Minkowski space?

Playing around with numerical light-like momenta $p^\mu_1,p^\mu_2$ (light-like meaning ${p_1}^\mu {p_1}_\mu={p_2}^\mu {p_2}_\mu=0$) and corresponding polarization vectors ...
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1answer
86 views

What causes these rainbow effects using a polarizing filter on an airplane?

I know that light reflected from a surface at 45° is polarized and that for a similar reason skylight arriving from a direction orthogonal to the sun is polarized too. Photographers make use of this ...
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1answer
247 views

Does my green laser pointer emit three distinct frequencies, or is my measurement flawed?

I was playing around with a cheap diffraction grating and my set of laser pointers, and I noticed that while the red and the blue pointers produce a single point in the spectrum, my green laser ...
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1answer
69 views

Laser diode spectrum vs LED spectrum, why so much difference in broadness?

I've been reading about how light is produced in both laser diodes (the most common types of lasers) and LED's. The mechanism seems very similar if not exactly the same: one applies a potential ...
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98 views

Does a source emitting visible light also emit infrared, microwave and radio waves?

I have a bulb which is hot enough to emit visible light and obviously it's hot enough to emit radiation which lies before the visible light temperature i.e. radio waves, microwaves, and infrared ...
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Why does the light instantly disappear when we switch off the source?

For example i take a box which is completely covered by the most perfect mirrors possible inside and inside that box i have a bulb whose bulb holder is also covered with the most perfect mirrors ...
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Why doesn't light affect a compass?

In our daily life a lot of photons of visible light, infrared and radio etc move around us. We know that light is an electromagnetic radiation. So why doesn't that electromagnetic radiation affect a ...
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100 views

Does a photon travel in all directions?

For example i am standing and a beam of light is passing in front of me. I am able to see that beam of light so does it mean that photons are travelling in all directions other than the photons which ...
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2answers
782 views

Why do we use microwaves in microwave oven?

We know that any object above absolute zero emits electromagnetic radiation. So hotter the object shorter the wavelengths. In the electromagnetic radiation spectrum radio waves has the longest then ...
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1answer
70 views

How to build a MOKE (magneto-optic Kerr effect) magnetometer at home?

I'd like to build a magnetometer at home. The type does not matter actually that much but it should be doable at home. The MOKE (magneto-optic Kerr effect) magnetometer at least appears to use ...
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How is ink's color produced?

From https://en.wikipedia.org/wiki/Complementary_colors The pairs of complementary colors vary depending upon whether the colors are physical (e.g. from pigments), or from light. These change ...
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85 views

Refraction of light marching band analogy

When trying to understand the refraction of light when it hits a slower medium, lots of people seem to be enlightened by the 'marching band' or 'marching soldiers' analogy, which 'explains' that when ...