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
77 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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108 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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0answers
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
60 views

Beating the Diffraction Limit with NSOM

I am trying to understand exactly why we can beat the diffraction limit when using near-field scanning optical microscopy (NSOM). For those who aren't familiar with NSOM, check out this article: ...
3
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69 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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187 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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50 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
56 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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49 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
91 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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0answers
233 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 ...
2
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0answers
64 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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33 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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84 views

Why is condensed milk glowing green under UV?

Teeth, nails and also сгущёнка (condensed milk) are glowing green when exposed to black light. What do they have in common? Is it a specific luminophore substance?
2
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108 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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42 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
24 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 ...
1
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0answers
25 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
68 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
116 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
109 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
23 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
62 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
102 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
173 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
101 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
51 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
128 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
43 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
48 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
32 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
24 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
49 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
171 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
125 views

Intensity of Brightest Fringe of a multi-slit Diffraction

Let's say we have a multi-slit experiment with N slits.Since the central fringe has the most intensity, is there an equation to calculate the intensity of central fringe in terms of the intensity of ...
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0answers
69 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
62 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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166 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 ...
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0answers
112 views

Spreading UV light? Fresnel lenses?

I'm making a little UV exposure box and I'm looking for a way to evenly spread out the UV light. I've used Fresnel lenses to do just this in the past, but that was for visible light. But from what ...
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0answers
34 views

Are “phase-specific” masks ever used in the context of double exposure lithography? Can these sorts of things exist?

I was recently reading an 08' paper on double exposure lithography: and I was wondering if there existed some material that could be used to create a mask for e.g. a 193 nm light source that was only ...
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0answers
66 views

Is there spatial data loss in light passing through transparent crystal?

There is perfect parallelepipedal bar made of transparent crystal with cubic lattice floating in vacuum. Faces of parallelepiped are parallel to lattice axis. There is image, forming checkerboard ...
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0answers
46 views

How close do two wavelengths of light need to be to produce a metamer?

Suppose I have two wavelengths of light ($r_1$, $r_2$) coming from a source. These rays are then reflected specularly on a surface. What is the minimum distance required for the two wave trains of ...
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0answers
199 views

Splitting light into colors, mathematical expression (fourier transforms)

I am trying to solve a problem that includes a function of the light hitting a certain area. My question is, how would I change a function $G(x)$ of photons hitting a certain area to include just ...
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0answers
257 views

Representing a polarization vector for light as a 'manifold of two state'

Explain me these projections please Context: I was reading a paper (Phys. Rev. A 68, 052307) which involved mesoscopic coherent states of light. There, in order to calculate the uncertainty of a ...
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0answers
122 views

How does a lens affect the field of view in a mirror?

If one looks into a mirror, he can see a certain field of view. If he places a convex lens that magnifies (or a concave lens that does the opposite) in front of the mirror, but so that he can still ...