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# Questions tagged [visible-light]

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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### Measuring speed of light with Fizeau apparatus [on hold]

Is the Fizeau apparatus a valid instrument/setup to approximately estimate of the speed of light? If so may some one try to explain it as simplified as possible? My confusion is with respect to the ...
23 views

### What information can our eye-cones actually extract from a spectrum of illumination?

If I understand correctly, the cones in the human eye work as follows: the three types have a degree of sensitivity for each wavelength. A cone is activated in a one-dimensional "degree of activation",...
223 views

### Compare how much a coherent laser visible green light beam spreads out with a incoherent green light beam.

Suppose I am mathematically modeling a visible green laser pointer beam which starts from the ground and ends up a half mile or full mile in the sky, projected upon an aircraft window 2 inches thick. ...
19 views

### Are there experiments specifically testing for electrostatic charge when light enters a medium?

I'm aware of the Faraday effect that occurs when light enters a medium, which suggests that there could be some interactions between magnetic fields and light: https://en.wikipedia.org/wiki/...
333 views

### Refractive Index Base Wavelength

The refractive index of a medium is usually stated as a single "number" rather than something depending on wavelength. However, it does in fact depend on wavelength. This lead to a question I haven't ...
32 views

### What is the definition of a Projection? [closed]

This may be a stupid question. But here it is... Can the scenarios below be reffered to as projections? 1) A projector projects an image onto a white screen. 2) A LCD display forms an image on a ...
141 views

### Why is Copper(I) Oxide Red?

This may appear to be a chemistry problem. But, after reading the Wikipedia article on copper(I) oxide, it seems to have more to do with semiconductor-physics. For example: … light travels almost ...
57 views

### Plasma Frequency of Indium Tin Oxide

What does determine the plasma frequency? The formula is: $$\omega_p² = \frac{4 \pi N e²}{m}$$ and for frequencies above the plasma frequency the material is transparent. So for indium tin oxide (...
365 views

### What are the wavelengths of the red, green, and blue lights used for making LED pixels?

LED screens in televisions and smartphones use pixels that use a combination of Red, Green, and Blue diodes that can produce any color when used in the correct proportion of intensity. My question is,...
12 views

### Is there a noun for a material that absorbs, scatters and luminesces?

I know Luminophore is used for molecules or nanocrystals which absorbs and emit light, and Scatterer is used for materials which scatter light (elastically or inelastically). I suppose it would be ...
49 views

### Why violet light bends the most? [duplicate]

I have read about refraction through a triangular prism,rainbow formation and other natural phenomena.They all told about the strong bending of violet light . I know that it has a shorter wavelength ...
132 views

### Why do clouds appear pinkish after rain?

Monsoon winds are blowing over India and after every rain I observe that the clouds are turning pinkish, even during the night. What causes such a phenomena? Or are the observations coincidence?
39 views

### Classical (non-quantum) explanation for the transparency of glass?

Is there a classical explanation for the transparency of glass? How did physicists explain the transparency of glass before quantum mechanics?
215 views

### Does the brightness of day follow simple harmonic 'motion'?

Is it really true that the brightness during the day on earth follows simple harmonic motion? My teacher mentioned this as an example but it doesn't feel obvious to me by any stretch of the ...
17 views

### The effect of velocity on dispersion of light

It is stated that red light bends less than blue light as white light is dispersed through a glass prism. I understand that red light travels faster within the glass because of its higher wavelength, ...
456 views

### Light focusing on long distances

If I have a green laser (500 nm wavelength) with initial beam diameter 3 mm, with proper lenses I can easily focus it to 1 mm or 0.5 mm for small distances like 10 cm. My question is can I focus it ...
12 views

### What effect will moving one light source closer to the screen have on the diffraction pattern of two coherent light sources?

Say that you have two coherent light sources to begin with, each the same distance away from a screen, but then, you move one of the light sources closer to the screen by a fraction of the wavelength ...
55 views

### Why does the soap bubble shine with the colours of the rainbow?

Is it because of refraction of light in water? a mixture of UV rays in sunlight? polarization of reflected light? interference of light reflected from external and internal film surface? or maybe ...
32k 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. These ...
250 views

### Phase difference for a central maxima in diffraction

For a central maximum in diffraction, contributions from all the parts of slits like point C and D are supposed to be in phase. I am not getting why contributions from all parts of slits should in ...
28 views

### Light Polarizer for Photons

This is maybe a noob question. I read that if unpolarized light is passed through a polarizer that only allows vertical polarization, then if this light is passed through a diagonal polarizer, only ...
34 views

### On seeing and especially in the dark

Our retina detects the change in the electromagnetic field due to the jiggling of the atoms surrounding us as I understand the seeing process. In the total absence of a light "source", however, why ...
280 views

### Polarized light from any surface?

From a textbook I read something like this: "When sunlight is reflected from a horizontal surface, the plane of incidence is vertical, and the reflected light contains a preponderance of light that is ...
61 views

### Focal Power of a Plane Interface

We know that when converging beam of rays are more converging after passing through an instrument, then we say it is of positive focal power. If angle of convergence doesn't change it is of zero focal ...
73 views

### What is the average energy of visible light photons, of what we perceive to be white light? (i.e. visible spectrum of 5500K radiation)

Visible light is anything between 1.65eV and 3.10eV, so the answer is somewhere between these values. Naively we could average this to 2.375 eV, but that would not be actual average of full spectrum ...
28 views

### Why is the road hard to see when it’s wet?

Ok, pretend it’s night time and I’m driving down the road with my headlights on. If the road is wet, it’s harder to see; that’s a given. But why? I’d assume it’s because less of the light from my ...
67 views

### Spectral colours

If we shine a prism with white light we get the light spectrum.I am interested what will happen if we block all the formed spectral components but the yellow light and let the yellow pass through ...
42 views

### Why do objects reflect laser light?

Why do non-red objects reflect red laser light? The color of things explained as "Objects reflect in the color that we see them, and absorb other colors." But if to illuminate, say, a yellow thing ...
43 views

### Why does certain clear plastic have an inner glow?

A type of plastic used in packaging for tamper resistant seals appears to have (what I can best describe as) a purplish inner glow under sunlight, and perhaps other bright light. In the image below, ...
36 views

### Is their a way to protect screens from being recorded? [closed]

This idea might sound stupid but... Is there a way a screen would be impossible to record using a prism? I’m not talking recorded by a software but recorded from a camera… If you put a prism layer in ...
33 views

### Vision bluriness

I don’t know much about vision so I hope one of you guys could clarify me… When people who have vision problems look at an object without their glasses, they’ll see this object with a certain level ...
17 views

### Reverse engineering visible color spectrum with night vision glasses

Here's the context from a discussion I was having with a friend. Let's say I have a picture on my phone. Would it be possible to watch this picture on my phone with night vision glasses who usually ...
166 views

### Energy Levels: Reflection or Absorption and Emission / Color of Objects and Emission Spectrum

This is a question that involves different topics that are related to each-other and I think it´s faster more enlightening to put everything in one question than to have multiple questions. First of ...
8 views

### Self-illumination vs lumimance

I'm using a graphics format reading library. There are three luminance modes for materials available, which I'm trying to wrap my head around: Self-illumination, which I interpret to mean "glow", as ...
120 views

### What type of mirage is this?

I am very new to the world of mirages and would like some information as to the type of mirage in this picture which I took this morning. It is the cargo ship African Kalmia which passed my location ...
353 views

### How to find out the wavelength for the blue led diode?

I need your help as I am stuck and I dont know where to start. I have got four blue leds diode that come with dark blue led lights that I really want to get the same led colours for my 3 fans, but I ...
27 views

### Why is the sky near the Earth limb warm-colored, even far from the sun?

I've seen many sunset pictures with explanations. The sun is red, the areas adjacent to it is orange, then yellow... because redder lights bend less, and the air is thick at that angle. Far enough ...
73 views

### How do materials absorb light

I'm curious how light is absorbed in materials. From what I understand, when an electron absorbs a photon, it gets excited to an energy level that is higher than the level it's in and the energy ...
69 views

### Doppler effect of light

Doppler effect for light is created for relative motion . But shouldn't light always approach us at the same velocity 'c' regardless of the relative speed ?Then how does Doppler effect work ?
201 views

### Why are some Air Gap Sparks Orange?

While testing the ignition system on my car with a variable gap spark tester I noticed that the spark was orange. I suspect that there may be a problem with the ignition coil such that there is ...
25 views

### Why does a photomultiplier tube (PMT) traditionally present better signal-to-noise ratio (SNR) than an avalanche photodiode (APD)?

Empirically, a photomultiplier tube (PMT) is said to present better signal-to-noise ratio (SNR) than an avalanche photodiode (APD). Some materials say that it is attributed to the higher gain and ...
4k views

### Where is a good place to learn classical optics for high school competitions?

I need to learn basic optics for a high school academic competition. Does anyone know any good places, preferably free and online, to learn the basics of optics, like lenses, angles of incidence, etc.?...
91 views

### Do photons emitted by grow lights really lose energy over the distance of a few feet?

I have watched videos where they test grow lights PAR(Photosynthetically active radiation) values at different distances. It seems to me that at the speed light is moving, a foot or two should not ...
77 views

### Why do headlights through a window move around a room?

As I lay in bed this evening a few cars have passed by and my blinds are down. As they come down the street, you can see a sliver of light on the wall on the side of the room that is in the direction ...
155 views

### Why are there concentric rings around a laser spot on the hand?

Take a look at this picture: You see, the outermost ring is red and then purple and then there is a small black region after which there is yellow and finally white. Why are these concentric rings ...
38 views

### How does the eye see a real image?

If we look at a convex mirror diagram, it produces a real inverted image at the bottom. Let's say a person's eye is above the object. How do the reflected rays reach the eye? since it's a concave ...
29 views

### Newton's explanation for interference [duplicate]

If Isaac Newton believed that light is a particle, then how did he explain the interference phenomena?
3k views

### Why should the ray become parallel to base in a triangular prism at minimum deviation?

In the case of minimum deviation, the refracting angles at two surfaces are equal. Then the ray inside the prism should be parallel to the base only if it is isosceles triangular prism. But everywhere ...