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.
14
votes
3answers
365 views
What are these rays that appear in photograph of sun?
In many images of light emitting objects we see such rays. Why do they appear ?
What is the math behind their number and direction?
-4
votes
1answer
70 views
Photonics: Slab As a Lens [closed]
The question can be found here: http://gyazo.com/fc4d26cd35e6ce368ad2a8ed504f1dcc
The refractive index it references can be found here: http://gyazo.com/94fd2f3b5ea7da9226c3acd56b0024c1
I'm not ...
4
votes
2answers
1k views
Why does earth look blue from outer space?
I know it's more than 70% water. But what has it got to do with earth's colour ?
0
votes
2answers
247 views
Is a monochromatic, or non-monochromatic light visible at greater distance?
Just what the title states.
Assuming identical conditions, excellent visibility -
If a 1W monochromatic light source, and a 1W non-monochromatic light source were viewed at a location in deep ...
4
votes
4answers
719 views
What happens when a photon hits a mirror?
When a photon of light hits a mirror does the exact same photon of light bounce back or is it absorbed then one with the same properties emitted? If the same one is bounced back does it's velocity ...
1
vote
0answers
95 views
Digital camera as a measurement device [closed]
It is know that digital camera is not the best device for quantitative measurements. However, it is often used in all sorts of atmospheric physics research, maily due to:
Low cost and availability. ...
0
votes
1answer
170 views
Dependance of temperature on color of metals
I asked this question because I supposedly did last year, Stanfor Klein which belongs to the Solar Energy Laboratory of the University of Wisconsin says that "the color of a car does not affect its ...
6
votes
1answer
306 views
Squinting at street lights
Simple question, I've always wanted to know the answer to this.
Why do you see a pair of lines radiating out from street lights when your squint at them? I can't think of a better way of describing ...
2
votes
1answer
334 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 ...
5
votes
3answers
301 views
Triple slit experiment
If the experiment is done with single photons and a "detector" at one of the slits the interference pattern breaks down.
What happens if three slits are used with single photons and a "detector" at, ...
1
vote
5answers
144 views
Photoelectric effect without light rays
For electromagnetic waves we have the photon association, one imagines light as particles "flying around".
What is the analogy for a constant electrical field, one which doesn't change in time ...
0
votes
2answers
429 views
Red light on blue object (for graphics software)
I'm trying to make a program that simulates shadows in a 2D environment and I need some help in determining how things should look.
For example, if my light source is red and the illuminated object ...
0
votes
3answers
377 views
What colour is nothing?
To me this is very confusing, but I hope we can discuss it and find a solid answer to the question.
If you were somewhere where there was absolutely nothing, what colour would your eyes see?
2
votes
1answer
354 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 ...
1
vote
2answers
431 views
Reflectance vs. Thin Metal film Thickness Graph
Is there formula that gives reflectance of very thin film of given metal (tens of nanometers) to the visible light of given wavelength(808nm) ? Which properties of metals are needed for the formula ?
...
0
votes
1answer
96 views
Is the acceleration and deceleration of a wave instantanious?
When an light travels in free space, it has a velocity of propagation equal to the speed of light.
However, then the light enters a medium with a refractive index of n, the velocity of propagation ...
-1
votes
3answers
166 views
Does the Lorentz transformation not apply to light?
Since you would know that light always travels at the constant velocity with respect to all frame of reference ....according to relativity whenever we are traveling at speed of light our time with ...
3
votes
3answers
339 views
formula for transparency of very thin film of metal
Is there formula that gives transparency of very thin film of given metal (tens of nanometers) to the visible light/light of given wavelength ? Which properties of metals are needed for the formula ?
...
0
votes
1answer
105 views
Can the inverse of a laser exist?
Speaking as a layman, I understand a laser works by exciting an electron so it returns to rest by emitting a photon. Is it feasible to 'damp' the energy level/s of an electron so it absorbs energy ...
0
votes
2answers
84 views
Painting wine botles
Yes, it's a physics related question. Read on.
I know from general knowledge that in order to produce a decent wine, you must keep it in a dark place. Therefore, from my knowledge of physics I guess ...
1
vote
1answer
133 views
Physics of Fireworks
This evening I saw the 4th July classic Fireworks in San Diego, and I was wondering about the most physical picture of what was happening. Does anyone have a good way to explain the detailed physical ...
0
votes
0answers
94 views
Why are subjects upside down when I look through my door peephole?
There is a convex lens 3/4" on the outside and 1 1/2" convex lens on the inside.
Each lens has one flat side facing out and one convex side facing in.
What can be done to correct this image?
1
vote
2answers
155 views
PV cell for invisible spectrum only
Is it possible to make a photovoltaic cell that would only absorb the invisible part of the electromagnetic spectrum, while letting visible light pass through or bounce off its surface?
I guess that ...
0
votes
1answer
74 views
Does regular sky clouds stops the sun's ultraviolet rays?
I have an argue with an ex-Doctor of Medicine about the amount of ultraviolet light reaching us under the clear day sun and under the 100% cloudy sky.
To what extent we can say that the sky clouds ...
2
votes
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 ...
0
votes
1answer
114 views
Does diffraction contribute to the Black Drop effect?
Two reasons are given to explain the black drop effect here, but I think I came up with a third.
Consider a two-dimensional cross section of the situation just after second contact and just before ...
5
votes
5answers
414 views
Why isn't it allowed to use a flash when taking pictures in a certain place?
When I go to, for example, a museum I try to take some pictures.
Sometimes the museum staffs forbid me to use a flash. Do you know the reason? I don't think it is related to photo-electric effect, ...
3
votes
2answers
303 views
Why do electrons around nucleus radiate light according to classical physics
As I navigate through physics stackexchange, I noticed Electron model under Maxwell's theory.
Electrons radiate light when revolving around nucleus? Why is it so obvious?
Note that I do not know ...
2
votes
2answers
341 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
382 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 ...
3
votes
10answers
604 views
Why do we think of light as a wave?
I've read that light travels in a straight line and has a wavelength of 400nm to 700nm. But I don't understand why does it have a wavelength and what creates its wavelength? I agree with the concept ...
0
votes
0answers
203 views
Get RGB value from a Color Wheel [closed]
Say I have a color wheel like this
http://bluelobsterart.com/wordpress/wp-content/uploads/2009/03/rgb-color-wheel-sm.jpg
Now how do I determine the RGB value at one particular point inside the ...
8
votes
3answers
432 views
Why isn't light scattered through transparency?
I'm asking a question that has bothered me for years and years. First of all, let me give some context. I'm a layman in physics (college educated, math major). I've read Feynman's QED cover to cover, ...
0
votes
0answers
51 views
Image intensity when light is located in front of camera
According to papers, Image intensity has relationship with light intensity,
$L = ch(v)$
where $L$ is image intensity, $v$ is light intensity, $h$ is a nonlinear function $0<h(v)<1$ and c is ...
4
votes
4answers
1k views
How to bend light?
As we all know that light travels in rectilinear motion. But can we bend light in parabolic path? If not practically then is it possible in paper? Has anyone succeeded in doing that practically ?
8
votes
3answers
277 views
How can a body be transparent?
How can a body be transparent? I need the theoretical explanation for the same. Has anybody succeeded in doing that practically?
1
vote
1answer
141 views
How does a strobe lamp stop a fast moving object?
A strobe lamp can be used to seemingly stop a fast moving object when calibrated.
Commonly used in quality assurance during production to inspect otherwise non-observable assembly line activity.
What ...
1
vote
0answers
156 views
Does Infrared Light passes through Active Shutter Glass?
The glasses that we use for 3D viewing does it allow infrared rays to pass through them. Infrared rays pass through normal glass right? I need the pupil illuminated through infrared LEDs so I need to ...
0
votes
1answer
136 views
Where do you get $I_p=\frac{P}{4 \pi r^2} sin \alpha$?
This problem is about color science and it is short but tricky: Where do you get $I_p=\frac{P}{4 \pi r^2} sin \alpha$, where $I_p$ is radiant intensity(color science: radiometric quantities). Look at ...
2
votes
1answer
583 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 ...
1
vote
1answer
138 views
Combining Multiple Light Sources
Ok, Lets say I have two point light sources A and B. Each light source has a power Pa and Pb, and is distance Da and Db away from a point P on a plane.
I can calculate the amount of luminosity at ...
0
votes
1answer
60 views
What kind of light is needed to light up Venus?
Let's say I would want to light up Venus, such that we can see Venus all day long and not have to wait for a Venus Transit. What kind of light would I need for it? How powerful would it need to be?
0
votes
0answers
195 views
Is Photosynthetic Photon Flux Density (PPFD) a synonym for Photosynthetically Active Radiation (PAR)?
Both have units of $\mu\text{mol m}^{-2}\text{s}^{-1}$ and refer to light in the 400-700 nm range - that activates photosynthesis. However, I just want to confirm that these are synonyms and don't ...
2
votes
1answer
117 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: $\cos\theta=\frac{\Delta}{r}$
0
votes
1answer
94 views
Exist some relationship between irradiance units and wavelenght of the incident sunlight?
Exist some relationship between irradiance units and wavelength of the incident sunlight?
What about irradiance? I want to establish a relationship between wavelength and irradiance, because I would ...
2
votes
1answer
142 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 ...
21
votes
2answers
2k views
Why is the sky not purple?
I realise the question of why this sky is blue is considered reasonably often here, one way or another. You can take that knowledge as given. What I'm wondering is, given that the spectrum of ...
2
votes
2answers
952 views
If blue light has a higher energy than red light, why does it scatter more?
As $E=hf=\frac{hc}{\lambda}$, blue light - with a smaller wavelength - should have a higher energy. However, it is the case that blue light scatters the most. Why is it that higher energy rays scatter ...
6
votes
2answers
621 views
EM wave function & photon wavefunction
According to this review
Photon wave function. Iwo Bialynicki-Birula. Progress in Optics 36 V (1996), pp. 245-294. arXiv:quant-ph/0508202,
a classical EM plane wavefunction is a wavefunction (in ...
1
vote
3answers
793 views
Hours of light per day based on latitude/longitude formula
I'm looking for a formula that will return the number of hours per day given a specific location. I was thinking that can be calculated as a difference of sunrise and sunset, but I see that there are ...
