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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Why can I turn light red or blue by holding my finger up to it?

This is a difficult phenomenon to explain. Imagine you have an opaque object partially covering a very bright light source, for example, an object held up against the sky. The left hand diagram is ...
4
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0answers
91 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 ...
4
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295 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 ...
4
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109 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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1k views

How do you estimate colour temperature based on the position of the sun in the sky?

I'd like to estimate the colour-temperature of sunlight (as applied in photography) based on the position of the sun in the sky for a mobile phone app I'm working on (app link from a more appropriate ...
3
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0answers
72 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?
3
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194 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 ...
2
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32 views

Printing zone plate with laser printer

I tried to print my own zone plates on transparent plastic with laser printer with this generator. I prepared a lot of plates with different settings - focus from 4 to 60 cm, 3 wave lengths, etc. Yet ...
2
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0answers
179 views

Why should angle of incidence be equal to angle of emergence for minimum deviation in a triangular prism?

When I was solving questions on Ray optics I encountered a question wherein I had to prove that when a ray of light undergoes minimum deviation through a triangular prism then both the angles of ...
2
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0answers
57 views

Spectroscopy from a classical light wave or photon only?

In chemistry we mostly regard light/electromagnetic radiation as a beam of particles or photons. This is a very useful model to explain molecular excitations and ionisations from quantum interactions. ...
2
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51 views

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 ...
2
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0answers
100 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 ...
2
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68 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 ...
2
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34 views

Quantum Efficiency Estimation

Might there be a way to do a rough estimate of the quantum efficiency of a photo-detector like a CCD or CMOS sensor based only on a picture taken with it? I've read papers and guides (like this one: ...
2
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116 views

Collimating and homogenizing a divergent tunable-spectrum light source

I have a light source (Xenon lamp) which has the possibility to be tuned over spectral range of 390 - 740 nm with 1 nm spectral accuracy . Bandwidth at each wavelength is about 20 nm . Output ...
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0answers
18 views

Fresnel Diffraction

In fresenls treatment of a plane wavefront when the aperture is infinty then intensity on the screen must be equal to the intensity of incident wavefront. Intensity comes out to be 1/4 times the ...
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0answers
18 views

Light bulbs Flashing on when disconnected

For the 2nd time I've had a lightbulb flash on in my hand after removing from the power socket. The first time the overhead light in my hallway was out for a couple of days before I got around to ...
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0answers
40 views

Can 2 photons make up the same colour as another photon?

So, my question deals with the excited electron shown above. (1st diagram) This electron can return to its ground state by either of two ways. One of the ways involves the emission of 2 photons. ...
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0answers
49 views

Why does Light change color through Glass slab?

I shone a green laser light(~532 nm) through a glass slab and what I saw inside was that the light beam was now red. Imagine a regular refraction diagram but color the beam outside green and that on ...
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0answers
37 views

Why do different color materal differ temperature in the same sunlight?

I have a blue, red, and green cup and put a thermometer in each. Of the 3 the blue cup had the coldest temperature inside, then green, then red. I understand there may be differences in the ...
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0answers
29 views

Intersection point of two wires

When I observe two thin wires (up to 1cm, relatively) at a distance, if those two wires are intersecting (but may or may not have physical contact) the absolute point of their intersection is ...
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0answers
38 views

Scaling of the CIE RGB color matching functions

In the CIE color system, the RGB color matching functions look like this when plotted (I'm unsure what the unit of the Y axis is) https://en.wikipedia.org/wiki/CIE_1931_color_space#CIE_RGB_color_space ...
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260 views

Relation between intensity of light and amplitude of electric field?

A question in my textbook involve finding the electric field amplitude at a point in space given the intensity of light. It uses the following equation to solve it: - ...
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0answers
56 views

How much light is necessary to form a black hole

I suppose that enough light in a small enough volume could create a black hole. What is the good quantity that can tell when light can or cannot make a black hole? Energy density? But there must be ...
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0answers
48 views

What would happen if a monochromatic light falls on an electron?

An electron is not strictly free, but in terms of QFT, we consider scattering events in an asymptotic framework where free particles would arise at $t \rightarrow \pm \infty$. So, I would like to know ...
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0answers
30 views

Wavelength limited resolution

I've read through answers to similar questions, and I haven't been able to find a satisfying answer. I've heard it said that in order to make out something, you need to use light with a wavelength at ...
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0answers
30 views

What are ways to measure light scattering for a science fair project? And how exactly does scattering work?

How does scattering work? And why? I am still in middle school. I am doing my science fair project on scattering and so far the resources I found have either oversimplified it or made it in a way ...
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0answers
92 views

Why do our eyes only pick up electromagnetic radiation which has been classified as visible light?

My understanding: Electromagnetic radiation is carried via photons - which enter our eyes and activate receptors depending on the amount of energy the photons have when hitting them. At what point do ...
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0answers
142 views

Is Wikipedia wrong about Huygens-Fresnel Principle?

Someone posted a question about why backward waves don't exist according to the Huygens-Fresnel principle: Why doesn't a backward wave exist? In following up on this question I read the Wikipedia ...
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0answers
135 views

What is this bright spot in the sky?

This is my first question here so please be gentle! I took this picutre a few minutes ago (35 minutes ago, currently 1828 here) As you can see there's a VERY bright spot on the right that shows a ...
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0answers
24 views

Geometric and radiometric distribution of light

I'm studying the behavior of the light in a scene, to know how much light arrives at a specific point of a surface and how much of it leaves from the point. From the documentation I'm reading, it says ...
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0answers
80 views

What is the minimal size of the spec of dust I can see with naked eye?

When sun directly shines thru the window - I can see small specs of dusts in the air. All specs have different sizes. Assuming direct sun luminosity is 100kLux, spec is a perfect sphere, reflection ...
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0answers
153 views

UV absorption decrease with an increase in concentration

I am working on a project measuring the absorbance of a solution which contains surfactant and hard brine. The solution has a constant concentration of surfactant and varying concentration of hard ...
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0answers
252 views

Variable wavelength LED

Does there exist a type of LED (or other type of light source) that can change it's wavelength depending on the current/voltage it receives on a second wire? If not, would something like this even be ...
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0answers
121 views

How do I translate from CIE xyY color space to combinations of monochromatic wavelengths

Let's say I have a chromaticity point, on the CIE xyY color space that falls within the real colors. (Like y:0.1, x:0.4 Y:1 -- magenta)[1] I also know that humans can perceive the same color, when ...
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0answers
53 views

How is it that light is reflected in this way in these photos?

I took 2 photos, in one there's a shutter and in the other there's the light that is reflected from the shutter to the ceiling. As you know and as you see from the first image, the shutter has ...
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0answers
152 views

YDSE and diffraction

In a single slit diffraction experiment we know that light bends around the edges. So can we treat Young's double slit experiment (YDSE) as a two slit diffraction since we're using two slits in that ...
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0answers
25 views

About atomic transitions

I accomplished my homework but it opened a whole pandora's box of things I do not quite understand, so I would appreciate help. In x direction linearly polarized light excites atom transition from ...
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0answers
47 views

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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0answers
57 views

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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0answers
35 views

Making sense of sinogram of perspex block in air

I'm confused trying to visualize what happened exactly during this experiment: Setup with a laser and a photo diode on the opposite side. A perspex block (2x2cm) in between. Take 200 measurements ...
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0answers
25 views

What sort of function would accurately model the change in daylight at sunrise or sunset?

Assume that you are standing on the equator in a flat, wide-open space and there is no moon or clouds. What sort of mathematical function would accurately model the increase in daylight when night ...
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0answers
29 views

Does illuminating a conductor with light energy less than its workfunction change the measured conductivity?

For example, does the light absorbed in an exposed metal wire increase the average velocity of the electrons, hence increasing mobility and conductance?
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0answers
16 views

Are there any pigments which can be altered via the use of electricty?

I was looking at alternative visual output methods for computer, phone and the like and was wondering, are there pigments, Red, Green and Blue preferably, that can have their intensity/opacity ...
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0answers
81 views

Use mirror to see every angle around me

An applied physics question: How can I setup a mirror all around an arm wrestling table so I can see all angles of what I'm doing? The arm wresting table looks like this With the wrestlers on ...
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0answers
51 views

Analogy for Rayleigh scattering

This morning's eclipse has me looking into Rayleigh scattering. I'm trying to think of a good analogy to explain it to somebody without getting too in-depth into electromagnetism and other subjects... ...
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0answers
211 views

What is this light pattern caused by LED matrix street light?

At our office, they have installed new downlights in the parking lot (street lights) based on a rectangular matrix of very bright LEDs, which are not diffused. They look something like this one: ...
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0answers
79 views

Absorption Spectrum

I just learnt what absorption and emission spectrum are. And our teacher introduced us to what Quantum Dots are. And showed us their absorption and emission spectra. And they look something like this ...
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0answers
65 views

How does a liquid crystal on Silicon affect the phase of incident light?

When a polarized light beam is directed to a phase-only LCoS system how is the phase modulated ? What is the physical effect behind ? Does voltage modulation has an impact on birefringence ?
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172 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 ...