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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3answers
271 views
What was the motivation behind suggesting the trichromatic theory of vision?
Background
In this thread, I asked whether it is true that the colors red, green and blue, through additive mixture, can make up any color. Turns out they can't.
However, when reading about the ...
2
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2answers
786 views
Wave / particle duality question for sound and light
Sound is usually referred to as just "sound waves" - we do not talk about a "sound particle" and only as a wave or "matter wave."
Could something similar apply to light i.e. that there really is no ...
2
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1answer
134 views
Solar energy and optical fiber
I'm not really good at science or physics, just wanted to ask about the idea (doesn't have an opportunity to test this).
Will this scheme work and what can be its efficiency?(The goal is to make ...
2
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4answers
137 views
Light refraction and causality
One way how to look at refraction by a dielectric medium like water or glass is that (phase) velocity of light decreases because it is the wavelength rather than the frequency of the light which ...
2
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2answers
28 views
Penetration of light in the atmosphere
While I was considering an answer to this question, I wondered how much light that enters the atmosphere reaches the ground without colliding with air molecules—if any. I've taken a good bit of ...
2
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2answers
103 views
why does a mirror show what is in front of it?
the only answer I can think of is that light is reflected from the objects in front of the mirror (visible color) and then reflects again off of the mirror to our eye, but im not quite satified with ...
2
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2answers
171 views
How does scattering work?
Why is the sky blue?
I was always taught in high school that light with wavelength $\lambda$ acts like a little particle that wiggles up and down through space (in proportion to its magnitude). I was ...
2
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1answer
570 views
Transforming a sound wave into a literal light wave. Is it possible?
Literally transforming sound into an actual light wave seems almost impossible. But transforming the sound wave into a light wave while containing a single mass? I know that sound can contain a mass ...
2
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6answers
2k views
Limit of human eye flicker perception?
I am designing a LED dimmer using software-controlled Pulse Width Modulation, and want to know the minimum PWM frequency that I must reach to make that LED dimming method indistinguishable from ...
2
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1answer
459 views
Visible light spectrum to color space
I need to be able to convert an arbitrary emission spectrum in the visible spectrum range (i.e. for every wavelength between 380 and 780, I have a number between 0 and 1 that represents the ...
2
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1answer
130 views
The range of light
It occurs to me that the empirical evidence shows that there is a point out in space where light stops coming from.
Putting aside the expansion of the universe for a second, and focusing strictly on ...
2
votes
1answer
326 views
Is traveling at the speed of light the same thing as teleportation?
If I were on one side of the room and moved at the speed of light to the other side of the room, to an observer it would appear that I teleported. If time stops at that speed, it would be ...
2
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5answers
2k views
Focal Point vs where you see the images
I am trying to figure out where is the focal point and where is the image. I read some information online about the point where you see the image is the focal point, but however, my supervisor ...
2
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3answers
460 views
High speed and low speed photons
Looking at the discovery of the neutron, and I came across this page: http://www-outreach.phy.cam.ac.uk/camphy/neutron/neutron3_1.htm
The animation on the left, talks about low energy photons and ...
2
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3answers
136 views
What starts the movement of a photon
Although a photon has no (rest) mass, it does have a measurable speed. Its movement can be altered by gravity. A photon "travels". If I turn on a flashlight, seen by someone at a distance, the photons ...
2
votes
1answer
99 views
Commercial Infrared lights
I purchased an infrared light. It's a 100 W Philips infrared lightbulb. Says it's infrared, but I haven't done any spectrum analysis so I don't know for sure if it's just red or really infrared.
As I ...
2
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1answer
104 views
How would one generate Brownian light? What would it look like?
When light is an equal mix of all visible frequencies, we call it white light.
By analogy, sound that is a mix of all audible frequencies is called white noise.
For sound, there is an additional ...
2
votes
2answers
328 views
How objects have different color in different lights?
As everybody knows that Black objects are black because almost all the light that falls on them is absorbed into the material. Little or no light is reflected back toward our eyes, therefore we see ...
2
votes
1answer
325 views
What are the properties of the partially polarized light on refraction?
When a ray of ordinary light is passed on the surface of the water the reflected light will be completely polarized( vibrations in one plane).
My question is what will be plane of vibration in the ...
2
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1answer
352 views
Rotating mirror - Foucault's measurement of light speed
Some time ago I came across a secondary web source on measurement of light speed in water made by Foucault around 1850. I append its redrawn scheme below (light is reflected from the rotating mirror ...
2
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1answer
116 views
Is it possible to send a single photon from a distant planet (say Mars) and detect its arrival at a site on Earth?
My question is specifically whether there exists a technique by which a single photon can be "tagged" or "encoded" in such a way that it can traverse our atmosphere and arrive at some sort of detector ...
2
votes
1answer
141 views
Can a charged black hole interact via electromagnetism? [duplicate]
Possible Duplicate:
Detection of the Electric Charge of a Black Hole
Light cannot escape from a black hole. However light is also interpreted as the carrier of the electromagnetic force. So ...
2
votes
1answer
102 views
Why is the shadow of earth red?
Reading this article about the forthcoming eclipse on December 10th, I noticed mention that the moon passes through the red shadow of Earth; I'd always held the impression that a shadow is universally ...
2
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1answer
290 views
How to set up a very simple experiment in optics?
This might come across as a very rudimentary question.
My fundamentals of Optics are weak. In the optics chapter of my physics text book I saw diagrams each depicting an object on the left and a lens ...
2
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3answers
306 views
Does the wavelength always decrease in a medium?
I was studying a GRE Physics Test problem where optical light with a wavelength of 500 nm travels through a gas with refractive index $n$.
If we look at the equations for wave motion and index ...
2
votes
2answers
161 views
Is there a reason for photodynamic therapy to not cause cancer if mobile phones might?
I don't want to open a debate about whether cell phones can cause cancer,
I read the thread: Could cell-phone radiation cause cancer?
For the sake of this question let's assume there's a chance for ...
2
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1answer
28 views
Relation of color and frequency for the visible spectrum
In this question the OP is looking for a way to see light that is outside of the visible spectrum without using electronic sensors. This got me wondering about the visible spectrum itself. Typically ...
2
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2answers
100 views
Seeing colors: photons vs waves
As an atmospheric physics major I am familiar with electromagnetic radiation in the atmosphere and what dictates what wavelength objects will emit at. When observing radiation in the atmosphere it is ...
2
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2answers
87 views
Decomposing light into frequency spectrum
Light hits a charge coupled element. The wavelength of the light somehow is translated into a color picture. Where can I learn about methods (algorithms) to decompose light hitting a CCD into ...
2
votes
1answer
128 views
Can an invisible light source cast shadows?
Let's assume that we have a mechanism for producing EM radiation suspended in the air, and that that mechanism itself is invisible to the naked eye (e.g. a microscopic light bulb on a microscopic wire ...
2
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1answer
61 views
A question about how light hits a surface
my question is about how photons travel from a light source and hit an object.
When you look at an object being hit by light the whole surface becomes brighter.
What i'm trying to understand is why ...
2
votes
1answer
99 views
What is the spatial mode of light or the spatial mode of a massive particle?
I'm extremely confused by what physicists mean by the spatial mode of light. I am also equally if not more confused by what the spatial mode of a massive particle is. Can anyone help me out by ...
2
votes
1answer
72 views
Can small clouds reflect enough light to hurt your eyes/blind you?
I looked out my window a minute ago and immediately noticed a very bright spot where a cloud and a jet/plane trail met. The spot was so bright that I thought the sun was behind it because it left that ...
2
votes
1answer
148 views
What's the difference between the equivalence principle and curvature of spacetime?
Calculating using the equivalence principle only accounts for half the deflection of light, whereas the other half is from curvature of space-time.
But isn't the equivalence principle the same thing ...
2
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1answer
180 views
Different colors in LED/LCD display when viewed from different angle?
I want to know why different colours appear when viewed with a different angle. Can anyone tell me why?
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2answers
339 views
Electron model under Maxwell's theory
I was not able to recall my memories, so:
What is the formula that states the frequency of electrons revolving around nucleus is equal to the frequency of light (or photon) emitted (or radiated)?
(I ...
2
votes
2answers
379 views
Do we see color with higher frequency first?
Out of the 7 colours of the rainbow, violet has the highest frequency and the smallest wavelength. Does this mean that our eye sees it first? If yes, then why? Does it travel at the same or higher ...
2
votes
1answer
116 views
Calculating a Deflection of Light Integral from Einstein's 1907 paper on Gravity and Light
$\frac{1}{c^2}\int_{\theta=-\pi/2}^{\theta=\pi/2} \frac{kM}{r^2}cos\theta ds=2\frac{kM}{c^2\Delta}$
An observation: $\cos\theta=\frac{\Delta}{r}$
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2answers
97 views
Luminescence when ripping (answered) and when pouring (not answered)
As a father to a small child, I have often observed this phenomenon but have until i posted this question not found the vocabulary to Google for it.
Can you explain what I am seeing?
In a darkened ...
2
votes
1answer
503 views
Effects of high frequency lighting on human vision?
I have a couple of different LED flashlights. One of them has three different "modes" of brightness, and the way it controls it is via pulse width modulation (PWM). Here is a picture that illustrates ...
2
votes
3answers
1k views
UV reflective surfaces
Do surfaces that reflect visible light efficiently also reflect UV light? If not, are there surfaces that do?
(I have a large array of UV LEDs that I need to make larger and more diffuse, so I'm ...
2
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3answers
124 views
If photons can be absorbed by electrons, wouldn't that mean light has a charge? [duplicate]
I am a biochemistry and molecular biology major. If photons can be absorbed by electrons, wouldn't that mean light has a charge? Electrons only attract positive charges. Isn't it?
2
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0answers
28 views
How does the Luminosity Function relate to the tristimulus sensitivity function?
In colorimetry, the irradiance spectrum is weighted with the luminosity function to obtain the perceived luminosity, and the tristimulus sensitivity functions to obtain the perceived ...
2
votes
1answer
67 views
Atomic physics through classical resonance?
I have a rather general question regarding the theory of Quantum Mechanics. To preface this question, consider a violin string. When a violinist exposes the string to a bow, this is exposing the ...
2
votes
1answer
260 views
Gravitational Redshift around a Schwarzschild Black Hole
Let's say that I'm hovering in a rocket at constant spatial coordinates outside a Schwarzschild black hole.
I drop a bulb into the black hole, and it emits some light at a distance of $r_e$ from the ...
2
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1answer
78 views
Question on Radiance equation
The radiance equation is
$$
L = \frac{d}{dA} \frac{2(\phi)}{dW cos(\theta)} (watt/srm^2)
$$
where $\phi$ is the flux.
I am thinking, should not be the cosine term on the numerator instead of the ...
2
votes
0answers
54 views
Was Einstein's Cross Predicted by Einstein's Theories? [duplicate]
Possible Duplicate:
How does gravitational lensing account for Einstein’s Cross?
Einstein's Cross is a fascinating phenomena for which I have asked explanation here. However, I'm also ...
2
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3answers
288 views
Why is the colour of sunlight yellow?
I was going through the preliminary papers of other schools and found a question that I did not know. It was "Why sunlight appears yellow?". Can anyone answer it?
2
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0answers
86 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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2answers
428 views
What's the relationship between an object's color and it's energy?
All else held equal, which has more energy: a violet-painted teacup or a red-painted teacup?
I know that violet light has more energy than red light, but does this mean that the inverse holds true ...
