Questions tagged [visible-light]

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.

575 questions with no upvoted or accepted answers
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9
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0answers
127 views

Why does light not propagate backward in dense media?

It is easy to see how light propagating in a dense medium destructively interferes laterally and constructively interferes in the forward direction. This is why light will travel forward in such a ...
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268 views

The color of deep space background of an arbitrary universe

While writing my notes on cosmology in general relativity and the Olber's paradox, I was wondering about the color of the deep background of space. Our universe is mostly black because light didn't ...
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1answer
126 views

Can we see stars in day time by making use of a blue notch-filter?

Given on a clear sunny day, the only light that is blocking the star light is the scattered blue light of atmosphere. If we make use of a notch filter, which blocks only the blue light, can we get ...
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147 views

Energy absorbed in Polarization of light

A polarizer absorbs all light that vibrates in a particular direction. Where does the energy absorbed by the "chain molecules" of the polarizer go? Does it change the structure of the molecules? Is ...
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0answers
30 views

How can compact fluoscent lamps light up?

My understanding of fluorescent tubes is that filament on one side gets very hot, undergoes thermoionisation and shoots electrons into the gas. The collision between a mercury gas atom and a fast ...
4
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1answer
69 views

Different Color Intenensities from simple ON/OFF RGB subpixels

I recently got interested in electronic paper. One design that I liked was the one from Mirasol: https://en.wikipedia.org/wiki/Interferometric_modulator_display However, what I don't understand, is ...
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241 views

Does Blue Light Really Have a Dark Side?

I was reading the following article on Wikipedia which discusses the dangers of blue light: Blue-light hazard is defined as the potential for a photochemical-induced retinal injury resulting from ...
4
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1answer
738 views

Under water light reflection of air in a cup vs water in a cup

The last time I was on vacation I was drinking on the swimming pool, and after I was finished with the drinks I started playing with the 2 plastic cups I had, and noticed that the air produces a ...
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0answers
581 views

Possibility of a free-space hologram

Holograms are real. But they are not what sci-fi calls holograms. From a simple geometric optics standpoint we can see that in order to create the illusion of an object there must be some sort of ...
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288 views

Optical Bloch oscillation

I have a doubt about how the optical Bloch oscillations happen in a 1D photonic crystal. I try to explain: in a photonic crystal with discrete translational symmetry in one direction I superimpose a ...
4
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3answers
892 views

Finding the illuminance from a triangular light source

Since most light sources in games are point-like, it's pretty difficult to approximate area light sources with point sources. As triangles are a universal form to represent 3D models (thus area light ...
4
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1answer
669 views

How much heat do colors absorb?

A common grade school experiment is to compare how hot different materials get in direct sunlight. See examples here, here and here for example. The premise is generally two identical objects of ...
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40 views

Do laser filaments propagate in a straight line over long distances?

In so-called filament propagation, a powerful laser beam can propagate through a medium without diffraction. This occurs because the beam focuses itself through non-linear optical effects. Self-...
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28 views

Lab Construction of LED

If given a semiconductor with known bandgap, how might someone construct an experimental LED within a lab? It seems common to prepare solar cells using FTO glass plates with a paste of semiconductor ...
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2answers
200 views

Why are gold nanoparticles red?

While watching the latest computerphile video (https://www.youtube.com/watch?v=FGiBHsUkVzU) I came across a solution of nanoparticles of gold , but to my surprise, they appeared as red, shouldn't ...
3
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1answer
113 views

While flying over Rome we noticed that during sunset, there was a green color between the red and blue of the sunset sky. What causes it?

The picture has only been trimmed and not edited. The green is visible when the red or orange tapers off into the blue. Is this different from what causes the green flash? We were flying from Rome.
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2answers
177 views

Light reflection from a charged surface

Will we see differences (in intensity or spectrum) of visible light reflection from surface of positively versus negatively charged metal plate (or any non-conducting materials)? Are there data about ...
3
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1answer
85 views

Why are powdered silver and powdered platinum black?

The quantum-mechanical (relativistic) explanations for the observed colours of copper, silver & gold don't appear to explain the black colours of powdered silver (& powdered platinum). Can ...
3
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1answer
124 views

Why is refractive index equals to speed of light upon phase velocity and not group velocity?

We have been using group velocity for most purposes as its the velocity with which the wave packet travels, they why do we use phase velocity for calculating refractive index.
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0answers
1k views

Reflection of "phone screen" light in a window

I've noticed that the reflection of a phone (or computer) screen in a window (or other smooth surface) has distorted colors (towards red-purple or green-yellow), which change as the screen is rotated ...
3
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2answers
515 views

How do those cheap shoebox-phone projectors throw any "decent" image?

You've probably seen them; shoebox phone projectors. They throw a very dim image, but I'm surprised it throws any image at all, since the lightsource is completely diffuse. Why does it still ...
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557 views

Can our eyes and ears detect phase information in addition to amplitude and frequency information?

Both eyes and ears detect continuous waves that impinge upon them - electromagnetic waves in the case of eyes, and sound air pressure waves in the case of ears. The amplitude of these waves is ...
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85 views

Thin Film Interference Maxima Calculation

I would like to calculate for which thickness, d, I have maxima. The Set-Up: I have a laser of wavelength 300nm that shines with normal incidence onto the layers. Now, I would like to calculate for ...
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246 views

Could sonoluminescence be the result of the Casimir Effect?

My question concerns Sonoluminescence. I was amazed to learn that collapsing cavitations in liquids generate temperatures greater than 20,000 Kelvin. Is it possible that the vast amount of energy ...
3
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1answer
93 views

Why can't we see better with an antenna?

Or alternatively: Why don't antennas look like telescopes? If visible light and radio transmissions are the same thing, why is there such a difference in the equipment we use for augmenting it?
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181 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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358 views

Is there a wavelength of electromagnetic radiation that can penetrate iron but reflect off iron oxides?

We can see corrosion or rust because visible light travels through air reflects off the material back through the air and into our eyes. But I am wondering if you could see the corrosion through on ...
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94 views

Two Photon Absorption dependence on Semiconductor Band Gap

It's well known that Two Photon Absorption coefficient is scaling with $E_g^{-3}$. Does anyone know what is the physical reason for this scaling? What is the physical theory behind this mathematics?
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309 views

Bandgap Spacing in Photonic Crystals

I am doing some self-study on photonics and have encountered the following question: We know that amorphous electronic crystals such as amorphous silicon have a bandgap. Can amorphous photonic ...
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1answer
92 views

Why is the law of reflection true?

When a bunch of photons strike a surface then they get absorbed by the electrons on that surface which then starts oscillating and thus re - emit some photons but they do it in the same plane as that ...
2
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1answer
40 views

Is there measurable heat at the point of contact with a material subject to light that is deliberately set up to interfere with itself?

When a laser is spaced to produce two beams separated by exactly 1/2 the applicable wavelength, interference occurs, and there's no visible light, at least to the human eye. But is there heat ...
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1answer
74 views

Does light travel in a straight line from a third observer's view?

We are always taught that light travels in straight path in a homogeneous medium, we even do experiments in primary school with cardboards with holes, "proofing" that light does not bend. ...
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36 views

Wien's law and colors

I know there are a Wien's law for frequency and one for wavelenght, but I'm wondering which one is the most accurate when it comes to our perception of colors. For instance for the Sun, the Plank ...
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0answers
68 views

Introduction to electromagnetic waves with easy math

My father would like to understand the physics of light (let's say Maxwell's theory, the wave-particle duality and special relativity) and he's asked me what book he should read. He's a quick learner, ...
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1answer
58 views

Anti-blue light gear. Some claim to filter blue light without changing color perception. Real or fake?

Please note: I do NOT wish to debate here whether blue light is really harmful or not. I just want to discuss what the anti-blue light technologies actually do. What I found: Please note: To avoid any ...
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1answer
19 views

Does the vanishing point of linear perspective occur when there's a 1-to-1 matching between the lights in the source, and the sensors of the observer?

Imagine we have a panel of lasers in a truly dark vacuum, together with a panel of sensors, facing each other, some distance apart. Further, imagine that the number of lasers within the light-panel is ...
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1answer
120 views

How do Airy disks happen in focused vs unfocused light?

In articles about Airy disks, I can't find whether they are talking about an aperture with a lens or mirror that focuses the light, or about a plain aperture. Most of the time they are talking about ...
2
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1answer
74 views

What is “spectral turnover”?

In a paper which deals with the spectra of radio frequency cosmic events, the word “spectral turnover” is used. What is “spectral turnover”?
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2answers
44 views

How does a non-infinite monochromatic plane ray of light know which way to refract?

I have been making a simulation of light traveling in medium from classical physics perspective and while trying to makes sence of a traveling wave packet i realized i don't understand something very ...
2
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1answer
42 views

Conduction band energy level under illumination

I am new to the field and my apologies if its trivial question. Consider a semiconductor having valence and conduction band at certain energy level. When it is illuminated with photons having ...
2
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2answers
88 views

What determines how transparent a material is?

Every time light hits a material, both reflection and refraction occurs. How does a material determine how much light gets reflected/ refracted e.g. glass vs silver? So far what I could find is light ...
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0answers
43 views

Hydrogen discharge tube emission spectrum different from emission during burning

In "How is it possible some substances burn with an invisible flame" it is stated that light emitted from burning hydrogen is almost invisible, more precisely: You say that hydrogen flames are ...
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0answers
142 views

Is every kind of energy quantised?

I know this is been asked on this site before but I felt unsatisfied by its one answer. I’m familiar with the concept of quantisation, I keep reading that “energy is quantised” but what do they mean ...
2
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0answers
262 views

Calculating Laser Beam Intensity Absorbtion

This question pertains to the ability to calculate the laser beam intensity , at a particular point in time when using lasers for the purposes of Cutting and Engraving Materials. The parameters at ...
2
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0answers
49 views

Estimating focal length using light

I am considering how to estimate the focal length of a dynamic lens (such as biological lenses) non-invasionally, i.e., without harming the animal. The mammal lens changes its shape depending on ...
2
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1answer
90 views

How do LCDs vary light intensity?

What exactly happens when an electric field is applied? Say we're dealing with a TN LCD, in a 'normally white' mode. With no voltage applied, the orthogonal grated plates cause the director of the LC ...
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0answers
53 views

Total amount of diffusely reflected light off of a sphere?

I have a numerical simulation that uses ray tracing to calculate the total amount of light picked up by a sensor, after diffusely reflecting off of an object. To validate this simulation, I'd like to ...
2
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2answers
62 views

What kind of light coherence is required for an image

If 1- Optically speaking, an image point (or pixel) is a light interference pattern 2- interference patterns require phase coherence then 3- the source of the image point must emit coherent light ...
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0answers
54 views

Can water be made more violet?

Water is intrinsically blue because of molecular vibrations. The topic is covered here: Only sea water appears blue in color, why this is not happening in river water? And here, which I post ...
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0answers
53 views

Feynman’s Treatment of an Opaque Wall

First time poster. I’ve been reading Feynman’s Lectures on Physics, and I’ve just finished reading his treatment on diffraction. Feynman described a method of thinking about an opaque wall that was ...

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