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.
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
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 ...
3
votes
2answers
162 views
Why do hot objects prefer to emit photons over electrons ? Is there electron-positron annihilation?
Why do hot objects prefer to emit photons over electrons ? Is there electron-positron annihilation ? If so , why ? Im confused by this.
0
votes
1answer
125 views
Confused about fire?
Im confused about fire.
The way I see it :
Heat creates (kinetic) energy in mass and this creates stronger vibrations of atoms.
When those vibrations are strong enough the electrons interact ...
-1
votes
1answer
288 views
Focal length of Convex lens [closed]
A lens forms a real image of $3\ \text{cm}$ high of an object $1\ \text{cm}$ high. If the separation of object and image is $15\ \text{cm}$, find the focal length of the lens.
2
votes
1answer
115 views
Can light be canceled by merging with an inverted wave?
Can light waves be canceled by merging them with their inverted waves? Seems like it would violate conservation of energy but waves are added together when they overlap, right? Where is the flaw in ...
2
votes
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 ...
-1
votes
1answer
76 views
Are the speeds of the different wavelengths of visible light different or varying in a medium such as air?
Are the speeds of the different wavelengths of visible light different or varying in a medium such as air? If so, please inform by how much?
Also, even if the wavelength speeds vary minimally, please ...
6
votes
1answer
160 views
Why both yellow and purple light could be made by a mix of red, green and blue?
We see the mix of red light and green light as yellow light (#FFFF00). The wavelength of yellow light lies between red and green.
But the wavelength of purple light lies outside of red and blue. ...
0
votes
3answers
385 views
Intensity of light
If we have 2 beams of light with equal intensities, but with different frequencies, wouldn't the one with the higher frequency generate more power?
If so, how come the intensity, which is in $W/m^2$, ...
1
vote
4answers
148 views
Is infrared light diffused on walls?
Lamps that produce visible light can light up a whole room because the ceiling and the walls diffuse light. This way, when there is a single lamp in a room, something that is in the shadows is not ...
-1
votes
1answer
178 views
How can you test what color different people perceive? [closed]
If I would show someone a yellow object and ask them, "is this object yellow?"
That person would say "yes".
But I could never know if my perception of the color yellow is the same as that other ...
-1
votes
2answers
65 views
Why photo cannot be captured while facing toward the Sun /
When the Camera is facing toward the Sun and a person is standing to and We're capturing his photo , all we get is a black shadow even when we capture with the flash light or anything.
Why does it ...
2
votes
3answers
762 views
Is there something special in the visible part of electromagnetic spectrum?
I always wondered how much information we get from color. Things we see have different colors; edible products change color when began to spoil so we have a notion what color a fresh product should ...
9
votes
2answers
693 views
Is the “How to break the speed of light” minute physics video wrong?
I am referring to this video, on YouTube, by minutephysics, which has quite a lot of views.
In the video it states that if you flick your wrist while pointing a laser that reaches the moon, that the ...
1
vote
1answer
404 views
Why doesn't my pinhole camera work?
We all know that light travels in straight a line, which can be proved by pinhole imaging as in the picture shown :
But when I'm doing this little experiment with an apple, no matter how I change ...
40
votes
10answers
4k views
Is it possible that there is a color our human eye can't see?
Is it possible that there's a color that our eye couldn't see? Like all of us are color blind to it.
If there is, is it possible to detect/identify it?
1
vote
3answers
79 views
Redshift of light in dark matter
Following Edwin Hubble, it is widely believed that the universe is expanding, which is based on the red-shift of light from distant objects. Can dark matter cause light to be red-shifted and make it ...
2
votes
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 ...
0
votes
0answers
34 views
Need to write a function that computes the UV index
I have found a lot of people talking about how to compute the UV index, but have not found an example that shows the actual equations, so I could adapt them into an algorithm.
Probably the closest ...
2
votes
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?
7
votes
1answer
143 views
Strange light polarization effect?
I spent a while working with MgF2-windowed xenon flash / discharge lamps. Primarily, I characterized their spectra with two normal-incidence spectrometers against a calibrated Deuterium lamp. In this ...
0
votes
4answers
145 views
Seeing The Light in a Black Hole
I assume if light can't escape a black hole, then light is in a black hole. Does the light 'shine' inside a black hole
0
votes
2answers
179 views
What is the color of Water?
What is the color of Water? I am not talking about large water bodies like Ocean or lake but a glass of water. If it has no color how can we see it?
5
votes
3answers
257 views
How many percent of the visible light reaching the Earth are from other stars than the Sun?
How many percent of the whole visible light reaching the Earth are from other stars than the Sun?
Is it maybe 0,5 - 1% or is my guess already too much?
I am interested mainly in visible light, but ...
3
votes
1answer
271 views
Transparency of solids using bandgaps and relation to conduction and valence bands
I think I understand how a solid can appear transparent as long as the energy of the photons travelling through it are not absorbed in the material's bandgap. But how does this band gap relate to ...
7
votes
2answers
136 views
Does light have timbre?
Timbre is a property associated with the shape of a sound wave, that is, the coefficients of the discrete Fourier transform of the corresponding signal. This is why a violin and a piano can each play ...
6
votes
2answers
176 views
Blue-shifting as opposed to violet-shifting
A recent XKCD comic implies that the sky is blue as opposed to violet due to human physiology, and that animals more sensitive to shorter wavelengths will perceive the Earth's sky as the shortest ...
4
votes
1answer
131 views
What is the colour of starlight?
I'm interested to know the colour of starlight - particularly in rgb terms, I'm pressuming it's either white, or very close to white, but I'm interested to know how close.
To make it slightly more ...
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 ...
4
votes
1answer
160 views
Photons arriving from the Sun
Given that the Sun is a bit less than 10 light minutes away from Earth, is it correct to assume in principle (I understand actual processes in the core of the Sun make the situation at a photon's ...
0
votes
1answer
97 views
Colors in the secondary rainbow reverse of that in the primary rainbow
Why the colors of Secondary rainbow is reverse of that in the color in the Primary rainbow?
What can be the possible reason among the following options
Because it is formed by one internal ...
1
vote
0answers
147 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 ...
1
vote
0answers
213 views
Malus' Law (Polarization) [closed]
Consider the image below:
Let $\theta_2$ be the angle between the axes of transmission of Polarizer 2 and Polarizer 3 and $\theta_3$ be the angle between the axes of transmission of Polarizer 3 ...
0
votes
2answers
107 views
Building a LED lamp, which is the brightest? 3 LEDs of 2500 mcd or 1 LED of 6000 mcd?
I want to build the brightest lamp, for it to be seen at daylight, should I use 3 2500 mcd LEDs or 1 6000 mcd?
And also Why?
3
votes
1answer
88 views
Angle of rays leaving a light source
I'm working on ray tracing and I'm trying to understand the impact of the angle at which a light-path intersects the surface of a light source on the amount of light that source delivers to the path ...
3
votes
1answer
199 views
plotting an sRGB gamut Chromaticity Diagram starting with xy coordinates
Starting with xy coordinates I would like to plot a chromaticity diagram displaying just the sRGB gamut portion of the CIE xy chromaticity diagram.
For each ...
5
votes
1answer
263 views
Why does the sun “shine brighter” some days?
Today, the sun seems extremely bright; more dazzling than usual, and even the roads seem to be brighter so it's not just when you look up in the sky. Is more light actually getting through (perhaps ...
1
vote
0answers
153 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 ...
0
votes
0answers
40 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 ...
10
votes
1answer
219 views
Why does the spotlight reflected off of a rectangular mirror tend to become circular?
Background and setup
When I was 12 I used to like a girl, we were almost neighbors and it was essential that our parents don't find out. So whenever one of us wanted to call the other they'd signal ...
0
votes
1answer
626 views
Index of Refraction
The scenario:
A ray of light strikes the center of the (a) flat surface and (b) curved surface of a semicircular glass medium with the angle of incidences in degrees of 10, 20, 30, 40 and 50.
The ...
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 ...
-5
votes
3answers
185 views
Could some Red and Blue shifts be the result of light passing through “dark matter”?
As i see it, light behaves in certain ways, as the Double Slit experiement shows,
So when light comes into contact with dark matter, it becomes both a wave and a particle, the wave is bent around the ...
1
vote
0answers
66 views
Photon Statistics of a Coherent Gaussian Beam [closed]
Assume that a 100 pW He-Ne single-mode last emits light at 633 nm in a TEM00 Gaussian beam.
(a)What is the mean number of photons crossing a circle of radius equal to the waist radius of the beam ...
0
votes
1answer
159 views
Dispersion & Absorption in Optics
1) I understand light dispersion. But, I wonder what happens if I used a lens to focus it into a small point. Would it be a white point (would it reverse dispersion) or would I have a multicolored ...
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 ...
-1
votes
1answer
77 views
Determine when a light is going into the object [closed]
Please look at this image: (http://mypages.iit.edu/~smart/acadyear/refract.gif)
How can I determine when light is going into the object?
Actually, if there is, what is the simplest way to ...
2
votes
3answers
7k views
0
votes
1answer
396 views
Huygens Principle and principal of rectilinear propagation of light
Suppose I have an wave source and light waves are radiating from it. If I have a point source, then after a time t, with a radius of ct I will have a circular wave front.By Huygens principle each ...
