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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Explain the notion of light/electromagnetic waves/photons to a non-physicist

A non-physicist asked me about special relativity. My explanations naturally were based on gedankenexperiments involving light. This forced the question: "What is light? It is particles, isn't? Or is ...
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7answers
5k views

How do I see things of the bright room, being in the dark room?

Visible light emitted or reflected from the objects around us provides information about the world. If I sit in a dark room, and see the bright room outside, I am able to see all the objects of ...
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5answers
2k views

Radio antenna producing waves in the visible spectrum [closed]

If a radio could produce waves in the visible light spectrum, what would the result be? This is a thought experiment that I've pondered for a few years now. I realize there are a few/many real-world ...
4
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3answers
330 views

Is the number of rays projected by a source of light finite?

Take a source of light which gives out infinite number of rays, each ray with finite number of photons and each photon with a finite amount of energy, Then, Aren't the number of photons become ...
4
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3answers
847 views

Why does Snell's law not factor in wavelength?

If dispersion is caused due to different wavelengths bending with different angles, how is Snell's law right in generalizing it as $\sin(i) / \sin(r)$? Or am I missing something?
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3answers
9k views

Why does light always travel in a straight line?

No matter the frame light is in, it always moves in a straight line in that frame. Why is that? It doesn't seem like something to me that should necessarily be true. If some one runs forward and sends ...
4
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3answers
290 views

Why does the point of intersection of two shadows look brighter?

When I sit in my garden during the day I always keep looking at the two intersecting shadows of two rods. It looks something like this: What I find weird about it is that at the point of ...
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3answers
4k views

Why is moonlight less colourful than yellow light?

Just what the title states; and this isn't an original question: On full-moon, moonlight is almost as bright as mid-dawn; yet there is hardly any colour visible. This is not the case with sunlight. ...
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3answers
496 views

Why doesn't a ray of light have enough momentum to make us fall?

Why can't light be so powerful that it has enough momentum to make us fall?
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2answers
3k views

Do x-rays and gamma rays also contain photons like visible light does?

Do x-rays and gamma rays also contain photons like visible light does? If so, then what makes photons of visible light and other waves different? The rest mass of a photon is zero, but as it moves at ...
4
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2answers
2k views

Why are most accurate reflective surfaces not white?

Since white is our perception of reflection of light, why are mirrors and other metallic objects that are more grey or silvery capable more reflective than a white object? This is somewhat related: ...
4
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2answers
392 views

Seeing one's back on the event horizon

If we would hypothetically be exactly on the event horizon, we should see our own back, because of the circular motion of photons on the event horizon, right? But what would be the image size, or $-$ ...
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3answers
375 views

Is it possible to transfer light from edge to edge of transparent material?

I don't know much about physics but i believe that this is the place to ask my question. I'm using 3 monitor setup like this: the plastic bezels [ ] are extremely annoying. in order to make them ...
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2answers
1k views

At what distance could you see andromeda with the naked eye?

We've all seen the telescope photographs of andromeda galaxy: I'm wondering if it were possible to travel close enough to the andromeda galaxy could you achieve a same perspective with the naked ...
4
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2answers
492 views

Why Does The Moon Apear White/Grayish and The Sun Yellow? [duplicate]

The Sun, as we all know, is white. Because our atmosphere scatters light the sun appears yellow to us hear on earth. So, why isn't the moon also yellow. Doesn't our atmosphere scatter its light. How ...
4
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2answers
543 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.
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2answers
332 views

Sensitivity of eye

In which color human eye is most sensitive?
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1answer
6k views

Purple doesn't occur in rainbow - or does it?

Usually, when asked whether the purple color exists rainbows, an answer similar to this is given: The purple color is perceived by human eyes via the activation of both red-sensitive and ...
4
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2answers
319 views

Computations using light

I recently found out about analog computers. They really intrigue me. I've seen a few videos on how mechanical computers work. I also know that there are electric analog computers too (I have no clue ...
4
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2answers
620 views

Reflected and refracted light have same frequency as that of the incident light frequency. Why?

My text book says- When a monochromatic light is incident on a surface separating two media, the refracted and reflected light both have the same frequency as the incident frequency. Can anyone ...
4
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2answers
7k views

How do you measure wavelength/frequency of light

I'm sure this is a trivial question for someone who knows something about electromagnetic radiation, but: how do experimenters measure the wavelength/frequency of light? For example, how do we know ...
4
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1answer
741 views

How bright is a 150 W incandescent light bulb?

When I was a boy (I live in the UK) most light bulbs were incandescents and they were labelled with their wattage. The brightest bulb you could get was an 150 W incandescent light bulb. Today there ...
4
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3answers
723 views

Why can I split white light into separate colors with my eyes

I was sitting in a meeting at work today. When I looked up there was a projector facing the rear wall letting out a very bright white light (the projection). When I look right at it, all I could ...
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2answers
2k views

Can a dot of light travel faster than the speed of light? [duplicate]

Say I have a laser. If I spin the laser so that the beam sweeps in an arc along a very distant object, could that dot travel faster than the speed of light? In Diagram form:
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3answers
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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 ...
4
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3answers
188 views

Is it accurate that light loses energy in the absence of gravity and gains energy in its presence?

I just read an article about the supervoid they found and this is suggested. If so, then I am more and more fascinated with the ties between light and gravity. Let me emphasize, every article that I ...
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3answers
199 views

Will the current carrying solid conductors emit light?

If we pass current through a gas, like in the discharge tube, the electrons will accelerate in the electric field. The accelerated electrons will collide with gas molecules, and transfer some of their ...
4
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1answer
701 views

Very large absorption lines in stellar spectrum

I was puzzled by the wide absorption lines in a stellar spectrum I found. The following is what I expect absorption lines to look like - thin, crisp lines: However, I found this stellar spectrum, ...
4
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1answer
50 views

Do all narrowband filters tint the field of view?

I observed color in a nebula for the first time this past weekend when looking at the Ring Nebula through my Orion XT8. I noticed a bit of red on the outer edges. I placed my Orion Ultrablock ...
4
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1answer
175 views

If refraction slows down light, isn't it possible to hold light still?

I have a quick question about the refraction of light, and I'm sorry if it seems a bit simplistic or even stupid, but I'm still learning. We know that when light passes through a denser medium, it ...
4
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3answers
298 views

Why does shining a laser into an iPhone camera create these shapes?

When I shine a laser light into an iPhone 6 camera I get these weird shapes: The shapes are in no way in the background behind the laser. What causes these to appear? I know about typical lense ...
4
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2answers
361 views

A light so strong it has a shadow

I have recently taken an interest in shadows. I know that in order for a shadow to exist that you must have a solid in the way of the light. My hypothesis is that there can be a light so strong, like ...
4
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2answers
237 views

Is it possible to have a perfectly black material?

After reading this NASA article about the "blackest material", the following stuck out to me. The tiny gaps between the tubes absorb 99.5 percent of the light that hits them Is it possible to ...
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4answers
1k views

Does optical fiber preserve the angles of incoming light?

I am reading up on optical fibers and there's one thing I haven't understood yet: Does an optical fiber preserve the angles of incoming light? For example, if we light two LEDs in front of an ...
4
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2answers
172 views

Is ocean color affected by Rayleigh Scattering?

We know that sky color is due primarily to Rayleigh scattering. Is Rayleigh scattering the dominant effect for ocean color too?
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2answers
1k views

Does diffraction occur before interference?

In the double slit experiment, light passes through two slits and the waves interfere and form an interference pattern. A single slit is required for diffraction. So, I was thinking about whether ...
4
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5answers
519 views

How can sunlight be white , but pictures of the sun be orange?

I was thinking about elementary physics today and realised: We learned and proved that sunlight is white. But i don't understand why when you look at a picture of a satellite orbiting the sun , it(the ...
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2answers
1k views

How can a green laser be reflected as orange?

My friend recently bought a high-powerd pocket laser pen (from China). It is green, and reflects off most surfaces as green. On some orange surfaces, it reflects orange instead. That is to say, we ...
4
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1answer
141 views

Is it possible to apply force to a light particle?

I know, the universal speed limit is the speed of light $c$. So, is it possible to apply more force to a light particle? What would happen to it if we could?
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1answer
113 views

How can absorption spectra form if atoms can't remain in an excited state?

I have been tasked to write a research paper on stars. However, I know very little about physics in general. I am learning about how we can glean information about stars by analyzing the light that ...
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2answers
1k views

Why slightly closing your eyes let you see the rainbow colors?

So I was sitting and looked at a street lamp outside my house. It is an ordinary lamp that looks something like that: This lamp emits white light and it is about 20 meters from my house. It was ...
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4answers
3k views

Young's Double Slit Experiment : What would happen if the “first slit” was too wide?

I was wondering what would happen to the fringe pattern displayed on the screen if the first slit (as shown in the picture), which is also known as "single slit", was made a bit wider. I read it in ...
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3answers
1k views

Ways of achieving parallel rays of light?

I am thinking of ways of achieving parallel rays of light. Let's say I have an object that emits light, for instance the display of my mobile phone. The display emits rays of light in every ...
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4answers
2k views

Can 2 beams of ultraviolet light intersect and be visible where they intersect?

Is it possible that if you have 2 ultraviolet lasers, that are invisible to the human eye, and if you aim their beams to intersect at some point, that the place of intersection will show a lower ...
4
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1answer
102 views

Why don't I see green flames more often?

I was just thinking today that I usually see red flame, and have seen plenty of blue flame, but not green. My naive presumption for coloration of flames would suggest that I would see more green, so ...
4
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1answer
128 views

Why can gold be drawn out finer than light?

The metal gold is extremely malleable. Gold is also ductile and one ounce can be drawn into 80 km (50 miles) of thin gold wire (5 microns diameter) to make electrical contacts and bonding wire. I ...
4
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2answers
125 views

Could you view yourself in high gravity situations?

I'm trying to understand what effects gravity can have on light. First of all, I don't understand how gravity can even affect it, since it doesn't have mass, right? That is probably a separate ...
4
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1answer
56 views

Shadow of a ripple?

Suppose a stone is thrown into a pool of crystal clear water and its a bright sunshiny morning. You can observe a shadow of the wave in the bottom of the pool. Why does this happen? Is it due to ...
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2answers
4k views

Lux and W/m2 relationship?

I am reading a bit about solar energy, and for my own curiosity, I would really like to know the insolation on my balcony. That could tell me how much a solar panel could produce. Now, I don't have ...
4
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4answers
685 views

Why do the passing objects' shadows run in the direction of the moving train?

While travelling in the train on the sunset, I have noticed the strange phenomenon. The shadows of the lonely trees and lampposts, that stay along the railroad, are moving on the wall in the same ...