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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1answer
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Is energy density of two $P$ W lamps the same for one $2P$ W lamp?

Do two lamps of power $P$ produce the same energy output as single lamp of power $2P$, assuming ideal environment? E.g. lamps do not occlude each other, distance between lamps is negligible, no ...
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Why can't we see light in between point a and b [closed]

Many have asked this question and I will tell you a secret truth. When are all born, we all open our eyes for the first time. When you do, all you see is brilliant white light, as if an enormous ...
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1answer
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Do enough photons from Proxima b make it to Earth that its surface could be imaged directly with a huge, but not astronomically so, telescope?

I hope I didn't miss someone answering something similar. I was doing a small thought experiment. And I was wondering whether you kind people would check up on my math. Say we want to build a ...
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7answers
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What really determins the color of light? [duplicate]

I have been considering this problem: Colour is characterized by which of following character of light? a)Frequency b)Amplitude c)Wavelength d)Velocity Different websites claim ...
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Does diffraction limit on light divergence apply to all beams?

The diffraction limit $\theta = {\lambda \over\pi w}$ is generally referenced as a theoretical lower limit on light beam divergence. However this limit seems to be based on the assumption that a ...
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5answers
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Intuitive explanation for why blue light is refracted more than red light? [duplicate]

I understand the equation explaining angles of refraction related to wavelengths. But I'm looking for a more intuitive approach/visual explanation? Perhaps related to QM?
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3answers
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About the lowering of the speed of light in non-vacua

I don't understand really why matter interacts with light so as to slow down wavefronts to a speed strictly below $c$, but still preserving that sharp wavefront-like signal. This is somewhat ...
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2answers
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Can I shake a charge to illuminate my surroundings?

If I put charge on the tip of a rod and shake it back and forth at the right frequency, can I illuminate my surroundings? According to my understanding of Maxwell equations this would create EM waves ...
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6answers
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How can a red light photon be different from a blue light photon?

How can photons have different energies if they have the same rest mass (zero) and same speed (speed of light)?
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4answers
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Why do photons follow specific path after reflection from a mirror surface if they can be emitted in any direction by electrons of mirror surface? [duplicate]

The electron absorbs the energy of photon(with specific frequency)and re-emits the photon.The photon can be emitted in any direction. So why do they get re-emitted in a specific direction after ...
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Is the moon illusion a physical or psychological problem? [duplicate]

Is the moon illusion a physical or psychological problem? Some say it's a physics problem, and some say it's a psychological problem. I think it ’s a physical problem. What do you think is the ...
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How does light interact with matter? [duplicate]

I think light as made of photons every time is absorbed and than re-emitted. This explains reflection and scattering. Is it true? I also think that photons can not interact with EM fields? It true?
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What's the closest I can get to seeing all the colors?

The human eye can see a wide range of colors, but most computer monitors can only display less than half of them. Any color they display have to fit within the triangle made by the three primaries ...
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2answers
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Do gases become more opaque as they are cooled or compressed?

So recently I was thinking gases (at least colourless ones) are more transparent in their gaseous state than liquid state. And as we talk of continuity in liquid and gaseous state (fluids) is it ...
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0answers
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How does the formation of a real image in a cinema hall occur?

first question here... I'd like to know the complete process of formation of the image on the screen of a cinema hall right from the light emitted by the projector to it entering our eyes. I'd be ...
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1answer
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Is color perception of an celestial object effected by red shifting?

Assuming I stand on the edge of the gravitational well formed by our Sun. If I was to move infinitely closer to the Sun- and was staring at it without a filter (and wasn't harmed in doing so)- would ...
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2answers
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Could something theoretically observe the first light in the Universe?

Light travels at 299,792,458 meters a second. If you look at something that is 299,792,458 meters away, you're observing light from 1 second in the past. If an observer's distance from a light source ...
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1answer
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Explaining light distribution trough a gap using waves and Huygens principle

According Huygens principle when a light wave goes trough a gap that is so narrow that only one wavelet can pass, it would spread out in all directions like in this image: (image from https://en....
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Reasons for mechanical wave inversion? [duplicate]

General idea (with strings): When a wave in a string in transmitted through 2 different media, a part of it is inverted and a part transmitted. 'Rules:' If a wave enters a region where the wave ...
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4answers
93 views

Peculiar Question: Can Sound travel through particles of Light?

It is a thought Experiment. Imagine a box that is lined on the inside with 100% perfect mirrors. Shine some light into that box and seal the box. The light will bounce back and forth between the ...
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0answers
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If both violet light and red light was incident on the center of a semi circular block, and refracted, would they have the same refraction angle?

As the violet and red light have the same speed in air, with the incident angle being less than the critical, with the violet light and the red light coinciding on each other, (like on top of each ...
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0answers
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Why cannot we see back of our head? [duplicate]

Suppose we are watching a star at night, we are able to see that star because the photons from that star reach our eyes, now since the photons emitted by that star will reach earth and if we ...
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0answers
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What is the color of viral particles?

I read today on twitter that because COVID-19 particle is very small (<100nm) and visible light wavelength is larger (>250nm) the virus has no "colour". I know that some molecular bonds vibrate at ...
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1answer
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How to calculate amount of reflected light from a retro reflective tape at a distance

If retro-reflective tape is reported to be 1000 cd/lux/sq m reflective at some angle, how much of initial light can be measured at some arbitrary distance? That is if I shine a 5mW laser beam at the ...
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4answers
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Electrons emitting photons. Real life example?

In highschool we are taught about Bohr's atom model and how electrons emit light/ photons when transitioning from a higher energy orbit to a lower energy orbit. First question Where does this ...
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1answer
27 views

Two positions of the convex lens for a fixed object-screen separation

Explain why, for a fixed separation between the object and the screen(i.e., d + d' is fixed) there are two positions of the lens at which the images formed on the screen are in focus (clear images or ...
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2answers
37 views

How can I make sense of the way (screen) colors are generated? [duplicate]

OK here is some common knowledge I have from the net: a computer screen has 3 constituent colors of red, green, blue. To make all spectra of stuffs it just combines them. We also know that red is ...
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1answer
54 views

What happens to light (waves) when it falls into a room?

For my project that includes to design an ideal window for studios and housing i need to know the science behind what happens to light that falls into a room. I know that the light rays, to some ...
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1answer
24 views

Why doesn't the orange light filter appear bluish if it transmitts orange and reflects or absorbs all other frequencies?

I was going through the absorption and reflection phenomenon of light and this question struck my mind as I was walking through the light filters. Why does orange filter not appear bluish if it ...
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0answers
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Easiest way to achieve low divergence beam coming out fiber

So I have a green (I plan to swap it with 940nm IR) LED shining the other end of an optical fiber and I want to produce a 5mm spot at 5cm. The conventional way to achieve this would be with a lens but ...
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2answers
80 views

What kind of information does light carry so that brain can “see” shapes and distances of objects? [duplicate]

I know that we actually see with our brain in a way that eyes only absorb the incident light upon them and they transform some sort of information to the brain and the actual "seeing" is done by the ...
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1answer
88 views

How can a picture of a virus be taken when they are not even 300 nm (wavelength of blue light) long?

We cannot take photos of protons because they are not at least the size of the wavelength that registers into visible light. I see photos of Coronavirus in the news everywhere where there is a clear ...
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How to use convex lens to magnify image without inverting

From my knowledge, convex lenses magnify and invert light rays that pass through it. So is it possible to use a second convex lens to make the magnified inverted image into a magnified upright image?
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1answer
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Conduction band energy level under illumination

I am new to the field and my apologies if its trivial question. Consider a semiconductor having valence and conduction band at certain energy level. When it is illuminated with photons having ...
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3answers
51 views

Bubbles (water) are transparent, then how can they produce white light in mass amounts?

Bubbles (water) are usually translucent, and transparent too. In the field of optics, transparency (also called pellucidity or diaphaneity) is the physical property of allowing light to pass ...
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0answers
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Why does an overlap of atomic orbitals in a solid cause a continuous emission spectrum? [duplicate]

A given explanation for a light bulb's continuous spectrum of emitted light was that energy levels in solids overlap, therefore all energy changes can occur. How can these changes occur? If an ...
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1answer
43 views

Order of coloured bands of light: red, blue, green, orange, red, violet, green, and violet

I am currently studying the textbook Modern Optical Engineering, fourth edition, by Warren Smith. Chapter 1 presents the following diagram and explanation when discussion interference and diffraction: ...
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1answer
29 views

Why is the two-term form for the Cauchy equation sufficient?

The general Cauchy equation for the relationship between refractive index and wavelength is given by, $$n = A + \frac{B}{\lambda^{2}}+\frac{C}{\lambda^{4}}+...,$$ but this is often approximated to $$...
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2answers
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Must a rainbow's observer also be able to observe the sun?

I think I may recall sometimes a rainbow going away when a cloud comes between myself and the sun. I know that the appearance of the rainbow is location dependent. But do we need the sun, rainbow, ...
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1answer
23 views

how much information can beam of light can have in unit area? Can it have entire Earth's image? [closed]

Can one have a big lense in distant Galaxy where he can see everything (like humans walking and so on..) that happening in Earth? (Though there is a delay that's not important)
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Radiant Intensity

Radiant intensity is power per unit area and area being perpendicular to propagation of energy. Moreover, intensity varies inversely with square of distance. My question is if a beam of light is ...
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3answers
93 views

Is there any relation between turn on voltage of LED and the colour emitted?

It is evident from the above V-I graph that longer the wavelength of the light emitted lower is the turn on voltage. I know that turn on voltage is voltage required to have significant current that ...
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1answer
34 views

Mirascope Holograms

So I just realised that 3d hologram fan projectors are now a thing, and the quality looks quite good (search Ashata 3d hologram fan projector). However, an inherent problem with them is that the image ...
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1answer
46 views

A question about supernova (explosion decay curve)

In the third paragraph of this article: http://www.astro.ucla.edu/~wright/tiredlit.htm It talks about supernova decay and how a 20 day decay would appear to be a 40 day decay at a distance that has ...
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1answer
52 views

Can white light have two spectral peaks?

I was looking at a graph on the receptive ranges of the 3 types of color sensitive photoreceptors in us humans, and I had the idea that if we place only two peaks at the right places, we'll be able to ...
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4answers
104 views

How can an electromagnetic wave behave as a particle?

Light is an electromagnetic wave and it possess both properties of a particle and wave. Looking at the image I can imagine how it behaves like a wave. However, I'm not sure how it can behave like ...
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1answer
56 views

If we had a good enough eyesight would we be able to see atoms and the fuzziness of the quantum world?

If our eyes had enough precision and calibration to see hundreds of thousands smaller scales than we do, surely our brains would also need a major tuneup to process it. But could our classical body ...
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0answers
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Factors affecting Diffraction

I know that the larger the wavelength, the more the diffraction. However, I have a few questions. Is the diffraction more when the wavelength is equal to the gap size, or when the wavelength is ...
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0answers
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Why is the ocean darker when it is windy?

There are a lot of questions and answers on this site about ocean color, but none of them addresses my question. I have found this too: https://science.nasa.gov/earth-science/oceanography/living-...
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1answer
73 views

Why the rays do not continue in a straight line when passing through a prism?

How does the lightning that is not going through a rectangle know? a ray that passes through a rectangle, continues in a straight line What happens to a prism made of retangles of different lengths? ...

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