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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.

456 questions with no upvoted or accepted answers
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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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89 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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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 ...
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1answer
57 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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218 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 ...
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1answer
500 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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139 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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564 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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245 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 ...
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3answers
770 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 ...
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1answer
80 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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1answer
47 views

Can someone explain why optical rotation occurs?

Optical rotation occurs when carbon atom is surrounded by different groups. But how does that affect the direction of light? And why does it happen only for plane polarised light? My thought - if ...
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1answer
69 views

Doppler effect of light

Doppler effect for light is created for relative motion . But shouldn't light always approach us at the same velocity 'c' regardless of the relative speed ?Then how does Doppler effect work ?
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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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173 views

Did diffraction bend this light more than 90 degrees?

Earlier I asked whether diffraction could bend light more than 90 degrees. earlier question Lambda gave me an answer. He stuck a razor blade into a piece of wood, and he shone a green laser at it, ...
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1answer
72 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 ...
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1answer
71 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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476 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 ...
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1answer
214 views

Does the brightness of day follow simple harmonic 'motion'?

Is it really true that the brightness during the day on earth follows simple harmonic motion? My teacher mentioned this as an example but it doesn't feel obvious to me by any stretch of the ...
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385 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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64 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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520 views

Richard Feynman - QED: The Strange Theory of Matter and Light

After reading the book QED: The Strange Theory of Light and Matter, an adaptation of four lectures Richard Feynman gave at the University of Auckland, I gained a greater understanding of QED. I am not ...
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198 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 ...
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1answer
91 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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165 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
148 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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332 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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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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290 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
2k views

Non-polarised light

We know the beam of light oscillates in electric field and magnetic field, both perpendicular to both the wave of propagation and each other. What does, however, a non-polarised beam of light look ...
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48 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 ...
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55 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 ...
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46 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 ...
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1answer
48 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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29 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 ...
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How are the matrices for the RGB to/from CIE XYZ conversions generated?

So far, I've seen two different sets matrices for RGB ⇄ CIE XYZ. One from the Rochester Institute of Technology: $$ \begin{align} \begin{bmatrix} X \\ Y \\ Z \end{bmatrix} &= \begin{bmatrix} 0....
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2answers
38 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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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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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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1answer
37 views

Can Tesla coils up frequency to visibility

So I recently built myself a small ish tesla coil to make my childhood dreams come true, and to further my small understanding of the electromagnetic force. Some people like the musical tesla coils ...
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100 views

Could you actually see the event horizon of a Black Hole?

For years I thought to myself that surely you'd be able to see the event horizon of a Black Hole when looking at it against the surrounding light. I thought that it would be similar to this: Where ...
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1answer
198 views

Can Rayleigh scattering explain the orange color of the Titan sky?

It is my understanding that Rayleigh scattering depends on both the length of the particle as well as the wavelength. Due to the similar lengths of molecular nitrogen and oxygen it is blue light that ...
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Why do far away hills seem blue?

When walking with my grandmother and father in the country recently on a sunny day, I remarked not only on how the hills further away seemed fainter (a fairly obvious observation) but that also how ...
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22 views

Photovoltaic Device and Photon Absorption

When dealing with a photodiode photons with lower energy (such as red light) penetrate deeper then a photon with higher energy (such as blue light). The responsivity of the photodiode has a lower ...
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48 views

Does the black-body radiation formula (Stefan-Boltzmann) change if the photon turns out to be massive?

The black-body radiation formula, the Stefan–Boltzmann law, is derived treating photons as massless. Questions: What would the Stefan–Boltzmann law look like if derived assuming that photons have ...
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2answers
64 views

Red-shifting due to emitting gravitational waves

Light waves exert their own gravitational pull and must be emitting gravitational waves, losing energy in the process. Does this mean that light becomes red-shifted as it travels even without the ...
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1answer
37 views

Perception of rainbows

Does the shape of a rainbow have anything to do with the concave shaped back of a raindrop, from which the light is reflected?
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1answer
179 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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228 views

Integrating over Snell's law with a varying index of refraction

I am working on a research practical and I encountered the problem of having to integrate over Snell's law. The exact problem is that I have a varying index of refraction, which is a function of the ...
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1answer
150 views

Experimental proof of light speed isotropy

Where is the experimental proof that observers travelling toward or away from a light source, will always find that light from that source measures the same speed, regardless of their own speed?