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.

learn more… | top users | synonyms (2)

-3
votes
2answers
87 views

Can you see back in time? [closed]

When you look at the stars, the light that you see is probably hundreds of years old. Which means that you don't know if they still exist. Does all this mean, that if you fly in a speed faster than ...
4
votes
1answer
63 views

Experimental determination of speed of light

How is the speed of light measured by the most current method i.e. using lasers and atomic clocks? Alternatively, is there a better method?
0
votes
1answer
43 views

Beam of electromagnetic wave, with radius of 3cm or less

I need to create a beam of electromagnetic wave, with radius of 3cm or less, for distance about few meters. What is the minimum frequency (maximum wavelength) that it is really possible?
1
vote
2answers
108 views

Can we get the refractive index of a prism by using white light?

Can we get the refractive index of a prism by using white light ? I guess since white light is non chromatic, it is not possible.
5
votes
4answers
576 views

Why is an opaque body opaque?

When does a body qualify to be called an opaque body? Is it anybody which cannot let visible light through it or is there any other definition? And when and how does a body allow radiations through ...
0
votes
5answers
78 views

Is anything coloured “infra-red”?

All our day-to-day objects are things we can see, and thus we can conclude that their colour lies in the visual spectrum. Is there matter that does not have a colour within the visual spectrum? What ...
2
votes
2answers
56 views

What exactly is color? [duplicate]

What is color? “The property possessed by an object of producing different sensations on the eye as a result of the way the object reflects or emits light”…. You might say. So take a white object ...
37
votes
6answers
5k views

Is there a physical reason for colors to be located in a very narrow band of the EM spectrum?

The portion of the electromagnetic spectrum that is visible to humans are wavelengths between 380 and 750 nanometers. I am aware that animals have different capacities than humans, but the EM ...
3
votes
2answers
52 views

Whats the reaction that creates light when I open BreatheRight strips? [duplicate]

Darken a room. Pull open the sides of a BreatheRight nose strip (they work for me, though may be placebo effect). Notice the blue light coming from the separating adhesive.
2
votes
3answers
320 views

If I turn the light off in a room why does the light instantly disappear? [duplicate]

So today I was asked a question which I found very simple yet I honestly couldn't explain (embarrassingly). One of my mum's friends who knows I'm a scientist asked me "If I turn the light off in a ...
0
votes
1answer
57 views

Path Difference Due to Angled Incident Light

If light incident on a diffraction grating makes an angle $\alpha$ with respect to the normal to the grating, show how $$m \lambda = d\sin\theta$$ becomes $$m\lambda = d[\sin(\theta - \alpha) + ...
3
votes
3answers
297 views

Making a plastic scintillator glow?

I have a plastic scintillator I had purchased off eBay, which is believed to be BC408 http://www.phys.ufl.edu/courses/phy4803L/group_I/muon/bicron_bc400-416.pdf Upon shining a small UV LED (10-40mA, ...
0
votes
1answer
52 views

How does Huygens Principle explain interference?

How exactly does Huygens theory about the propagation of wavefronts account for interference?
3
votes
3answers
67 views

Negative frequency contributions for very short pulses?

I am wondering if very short optical light pulses can have a Gaussian envelope? When I describe the pulse shape with a Gaussian than the frequency distribution has also a Gaussian shape. But if the ...
5
votes
3answers
1k views

What does the colour of a light bulb depend on?

There are light bulbs of different colors available (red, green, yellow, white, etc). What does the color depend on? Is it on the temperature of the filament?
1
vote
4answers
345 views

What's so special about the speed of light? [duplicate]

What's so special about the speed of light? Why do many equations in physics include the speed of light in vacuum $c$? Why do so many thing depend upon it? Why can't it be the speed of sound? ...
2
votes
2answers
100 views

Where's all the light going in the universe?

According to my knowledge, matter can not go faster than light, and light is emitted constantly in the universe from many types of reactions. If this is so, then isn't light constantly getting past ...
1
vote
1answer
66 views

Splitting a light wave

What I want to ask is what would happen if you split a single light ray (a photon) into two using a half silvered mirror? Would the emerging light rays have half the amplitude as the original one or ...
2
votes
2answers
107 views

Why does light fade from a room?

So basically in my toilet I have this really bright ceiling light, but when I turn it off it doesn't just instantly plunge me into darkness, but rather sort of fades out over a few seconds. It looks ...
1
vote
3answers
124 views

What conditions should be met to notice a Doppler effect on light?

What relativistic conditions should an observer meet to notice the Doppler effect on a sample light wave, and is it even possible for one?
-4
votes
1answer
53 views

is it possible to extract spectrum (color in general) from an animal [closed]

if i may ask....can this be ASAP? :3 my problem: okay this is going to sound lame, but i was wondering if it is possible to extract color (specifically spectrum) from an animal. this question ...
3
votes
1answer
36 views

Is it possible to improve the efficacy of light bulbs with a semipermeable mirror? (The greenhouse bulb)

Let us imagine that there exists a material that reflects infrared radiation, but is transparent for visible light. Could we take an incandescent bulb and add this material to the inner surface of the ...
1
vote
1answer
43 views

Pattern on mesh office chair emulates thin film interference for curved surface. Possible to form an equation?

I saw a chair that looked like this at the dentists office yesterday, and the pattern caught my interest, as the light patterns emulated thin film interference fringes formed by an object that has a ...
0
votes
1answer
42 views

AC wire radiation

I'm trying to test my recently installed MEEP program for a very simple AC current. I know that for DC current, Ampere's law dictates that the magnetic fields must drop off as 1/r. How does this ...
8
votes
2answers
1k views

Would using Cherenkov radiation for lighting be feasible?

Could Cherenkov radiation be used for general illumination, for example, to replace LEDs, light bulbs etc? I.e. are there, or could there be, methods to produce substantial amount visible light with ...
1
vote
1answer
78 views

Why seeing further in “timespace” does not add up?

I've read that astronomers have received a light (a photon) 13 billion years old. Here's my question: If we start to turn the clock backwards all matter, energy, etc should start heading to the ...
1
vote
1answer
46 views

One way mirrored hollow sphere [closed]

Imagine a one way mirror, where from one side it appears to be glass, but from the other side, it appears to be a mirror. Now, fold that sheet into a hollow sphere, so the inside is mirror (and I'm ...
4
votes
2answers
175 views

Is manufacturing roughness really the only reason we don't see optical interference in thick dielectrics like windows?

I had always kind of wondered why we didn't see interference in things like windows -- we were taught that the condition is that the thickness of the film/slab/medium just has to be an integral number ...
1
vote
1answer
150 views

Energy Dispersion in Young's Double Slit Experiment

In Young's double slit experiment, when you see the diffraction pattern, why does the intensity of the light fade out as you move from the central maximum? I think it has something to do with the ...
0
votes
0answers
26 views

Are there datasets with light spectrum samples and their respective 1931 CIE XYZ values?

I'm developing a software (.NET/Mono) library to work with color spaces and light spectrums, and I want to add many test cases in order to ensure software quality. I've programmed code to convert ...
0
votes
0answers
17 views

What's so special about the invention of Blue LED that a Nobel was awarded to its invention? [duplicate]

Why was this years Nobel Prize for Physics awarded to Isamu Akasaki, Hiroshi Amano, Shuji Nakamura for inventing the Blue LED? I know that if a Nobel Prize is awarded for an invention, it must be ...
0
votes
0answers
29 views

What makes fluorescent lamps lower in heat than high pressure lamps coated with phosphorus?

Why does a fluorescent lamp give off more pure visible light (without heat) than a high-pressure lamp? Is the heat given off by high-pressure lamps caused by the intensity of light being emitted from ...
1
vote
0answers
65 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 ...
1
vote
0answers
32 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... ...
2
votes
0answers
156 views

Nobel prize for (dangerous) LED lamps? [closed]

There are many scientific articles about the danger of LED lamps (see below from the LED magazine, from scientific american, from a governmental journal and from Harvard health newsletter): Light ...
1
vote
0answers
48 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: ...
1
vote
3answers
87 views

Why is the Moon not redder at moonrise/moonset?

Okay we all know about Raleigh Scattering, which makes the sky blue. And by the same token, sunsets appear red because sunlight traveling through more atmosphere will "lose more blueness" as it's ...
4
votes
1answer
65 views

How do mirrors look & behave atomically?

I was observing mirrors recently and I was thinking about how an mirror would look atomically. I was always used to looking at atoms as being colored that said, I was always concerned at how they ...
1
vote
2answers
43 views

constant speed elevator light beam paradox

I can't get my head around this problem. Suppose there is an elevator moving up at a constant speed relative to an observer outside of the elevator, far away from any gravitational effects. Suppose a ...
0
votes
1answer
52 views

How can monitors display a sharp image, if light travels in all direction?

The question title might be a misnomer, help me improve it. My question is, from my understanding, a light travels in all direction from it's origin point. Also I assume that in the example of a ...
6
votes
2answers
448 views

Homemade Spectrometer

Recently I have had ideas of how to build a spectroscope, but I'm not sure if it will work. As can be seen in the diagram, the experiment is simple: it consists of a laser that generates the light ...
0
votes
2answers
71 views

How does the human eye knows how far the object from which the photon was reflected?

A photon is emitted from a source and reflected off an object (or objects) until it hits the human eye. The color of the object we see depends on the photon wavelength. If photon travels with constant ...
73
votes
2answers
4k views

Why does my wooden door disperse light into a rainbow color spectrum?

On a clear morning, light comes through this window (viewed from the inside) It then hits the door on the opposite side (so viewing from the outside the door straight on the other side) There is ...
1
vote
0answers
43 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 ...
1
vote
1answer
37 views

How to get the direction of bending light?

When light passes from a more dense to a less dense substance, (for example passing from water into air), the light is refracted (or bent) away from the normal. My question, is there any ...
2
votes
3answers
122 views

What “exactly” happens when a ray is incident at the critical angle?

The question arose when my physics teacher taught me geometrical optics and told that the phenomenon of both refraction and $reflection$ occur by change in medium. First of all, I'm not sure about the ...
2
votes
3answers
182 views

What happens to photons after they hit objects?

If I am not wrong when light hits for example white wall most of the photons are absorbed and transformed into heat and few of the photons at certain wavelength are reflected from the object. So white ...
18
votes
3answers
863 views

Why is the sky dark at night? [duplicate]

The question is the well-known Olbers' paradox: If there are so many/infinite stars, in every direction, why is it dark at night? Where goes all the light we don't see? Discussing with a friend ...
34
votes
4answers
6k views

Why is the sky never green? It can be blue or orange, and green is in between!

I, like everybody I suppose, have read the explanations why the colour of the sky is blue: ... the two most common types of matter present in the atmosphere are gaseous nitrogen and oxygen. ...
0
votes
0answers
35 views

Rotating sheet of light

I am looking for references on "rotating sheets of light" generated from a point source. Mainly I am looking for applications. (I saw a use related to climate studies or weather forecasting, where a ...