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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248 views

How bright was the universe after Big Bang during photon epoch?

After 10 seconds of Big Bang, most of the leptons and antileptons annihilate each other leading to an outburst of photons. The universe was said to be dominated by photons resembling a glowing fog. ...
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Could ultrasound pings and triangulation really help de-scatter diffuse red light for imaging?

Does the science explanation in the latest OpenWater TED talk make sense in principle? The claim involves taking advantage of the doppler effect. Could someone give a more detailed explanation as to ...
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53 views

How do lens capture reflections clearly?

In an optical system which uses lenses (cameras, our eye) multiple rays from the same point are conveyed in a single point on the retina / image sensor. This is typically shown as in the image below. ...
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237 views

Are there any types of lasers that emit orange and yellow light?

That is, without the introduction of nonlinear optics for frequency multiplication. In the case of orange light, I've often wondered in orange minerals like Lead Molybdate (PbMoO4) fluoresce the way ...
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2answers
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Why aren't maximums at 1 wavelength for single slit interference?

I can understand why there are destructive points in single slit interference. It is because the path length difference between the "pairs" of rays have a path length difference of $\lambda/2$. What I ...
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Cherenkov radiation relativistic correction

I have to write a paper on Cherenkov detection. And got a bit of an issue on the relativistic particle/recoil correction of the Cherenkov angle formula. Normaly $$cos( \theta_c) = \frac{1}{n\beta} $$...
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11 views

Light traveling through ice and glass and then lightsensitive film

I’m not a physician but I’m facing a physical issue in producing some images. My light source is a photographic enlarger - light is coming through a lens. That light travels through ice, then glass ...
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2answers
112 views

Photons’ Speed (light speed) in vacuum [duplicate]

In a vacuum, are photons always traveling at 100% light speed? Can photons go any slower in a vacuum? They have no mass which means they can go at 100% light speed, but do they have to?
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4answers
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Can you change the wavelength of light keeping frequency constant and can you do the opposite as well? [duplicate]

Can you change the wavelength of light keeping frequency constant and can you do the opposite as well? I understood the basics but please don't hesitate to go deeper into the concept. Also, If you ...
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1answer
46 views

Visible light as fraction of the EM spectrum

I was asked today what percentage of the EM spectrum we can see. It looks like a simple question, and yet I don't know how to answer it. I know that the visible light has wavelengths between $3.8 \...
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3answers
319 views

Why is grass green? [closed]

How come grass isn't blue or pink, but apparently, it is according to this scientist it is every color but green. I also got told by my teacher that grass is only green and no other color. So I am ...
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Determine whether a mirror is convex or concave from image magnitude, distance and reality

An object is placed 1.5m in front of each of three mirrors, (i), (ii) and (iii) with the following results: i) The image is real and 1.5m from the mirror. ii) The image is virtual and 1.0m from the ...
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1answer
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Refractive index and optical fibre question

This is an A level AQA question: A signal is to be transmitted along an optical fibre of length 1200m. The signal consists of square pulses of white light and this is to be transmitted along the ...
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2answers
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What kind of light coherence is required for an image

If 1- Optically speaking, an image point (or pixel) is a light interference pattern 2- interference patterns require phase coherence then 3- the source of the image point must emit coherent light ...
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1answer
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How does the anti-gravity fountain work?

I just saw this video of an anti-gravity fountain on youtube, but I can't understand how you can reverse the flow of water. I know you can stop the flow of water by using something called a ...
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2answers
133 views

Why are there rings (halos) around street lights? Especially when it's foggy

I was in a car that was turned off last night for some time and the windows became foggy via condensation (moisture droplets building up on one side of window). Looking outside, I could see that ...
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3answers
195 views

How many yellow objects are there? [closed]

I thought and read about color mixing today. I made some counterintuitive discoveries, and i now have some thought experiments which i cannot test. I could print a yellow image but i use a different ...
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3answers
115 views

How does a wave become a color?

I am a mathematician and not a physicist, so please be gentle to me. The best explanation I found so far about light waves was here: https://youtu.be/7eutept5h0Q If I got it right, then light is a ...
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3answers
48 views

How does one perceive light in terms of value?

I'm coming from learning art, and I'm trying to figure out the way light perception works. If I got it right, in order to see the surface, it has to reflect rays of light in viewer's eyes, but the ...
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2answers
46 views

How to find absolute luminance of a pixel in a photo?

Suppose we have a photo camera, which can take photos from which we can find out relative luminances of various pixels. Suppose also that we can vary exposure times so as to measure scenes of very ...
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6answers
161 views

Can an electromagnetic wave travel less than the speed of light and yet perceived by the eye as a light?

When an electromagnetic field passes through different mediums, it is known that it will refract. And during refraction - since its frequency is kept constant - the only parameter that changes is its ...
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Do virtual images exist in the real world? [duplicate]

I have been reading an article here in physics stack exchange that talks about if it is possible to see virtual images, and i read an answer saying it is actually your brain that understands the ...
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1answer
42 views

What does the person looking from the point of the image which is behind see?

In a plane mirror, the image of an object is virtual and is behind the image of another object. What does the observer looking from the point of the image which is behind see?
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Thought experiment: if an observer can travel at the speed of light [closed]

What would the observer see if he could travel at the speed of light and shot a photon beam at the same time?
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Crookes radiometer showing radiation pressure

Originally, the Crookes radiometer was meant to measure the light intensity. For decades the explanation for its rotation was debated. It is now known that the rotation does not originate from ...
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1answer
56 views

How do we see if light scatters in all directions?

This may be a silly question, but I'm not sure how we see an object in front of us. If light hits the points of the object and scatters in all directions, how come we are able to form an image of the ...
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2answers
73 views

How does a camera or eye detect violet if the smallest wavelength pixel element only detects blue?

Since cameras have RGB sensing elements per pixel, and eyes' cones similarly detect color with red, green and blue variants. The spectral sensitivities of the eyes are something like the following, ...
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1answer
93 views

Why farther objects do not look dimmer?

As far as I understand it, a light bulb irradiance (and illuminance) fall off following the inverse square law with distance, however radiance does not. I wondered why we (and cameras) do not see ...
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1answer
43 views

Speed of light dependent on source velocity in other medium [duplicate]

Does speed of light depends upon the velocity of source in a medium (like water) other than space? if yes, does the speed gets added up when the light source moves in direction of light?
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79 views

Spaceship A and Spaceship B move in opposite directions at half the speed of light, and A fires a laser at B, does the laser light reach Spaceship B? [closed]

This question has been bugging me for a week now! I believe it would, but logically, I feel like I'm missing something. Please give a full explanation.
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How can compact fluoscent lamps light up?

My understanding of fluorescent tubes is that filament on one side gets very hot, undergoes thermoionisation and shoots electrons into the gas. The collision between a mercury gas atom and a fast ...
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1answer
41 views

Diffraction Gratings Composed of Spherical Particles (such as those in opals)

I was curious about simulating opals, and after some research, found that their amazing colors come from diffraction gratings. Although, it seems to be different from the gratings caused by what is ...
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Can water be made more violet?

Water is intrinsically blue because of molecular vibrations. The topic is covered here: Only sea water appears blue in color, why this is not happening in river water? And here, which I post ...
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Is the whole electromagnetic spectrum made of quanta?

My question is probably stupid (and maybe has already been answered on other posts), but I just started investigating quantum physics and I am struggling to understand the real meaning of "quantum". ...
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40 views

Where does dispersion actually take place?

Out of 1 & 2, which is most accurate? And, out of 3 & 4, which is most accurate? Do they both agree with each other? Please explain?
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2answers
79 views

Why is gaseous carbon dioxide transparent? [closed]

Some carbon-heavy products of combustion, e.g. soot, are black, as is carbon in other forms, e.g. graphite. This seems to suggest that carbon is black. But then how can $\text{CO}$ (carbon monoxide) ...
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About the color [closed]

When I am reading my book keeping my head steady, everything is fine. But when I bend towards the right or left of the book, or the phone screen, things become darker (it happens more in phone screens)...
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30 views

What kind of wave is light? [duplicate]

When people say about wave-like nature of a photon, what do they mean: Pressure-like wavefront - it moves as a sphere (or a bulge on a surface) and then if we measure pressure at one single point (...
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2answers
172 views

Why can't I see whole galaxies with the naked eye?

I have read these questions: At what distance could you see andromeda with the naked eye? Do all the individual stars that we can see in the night sky belong to Milky Way? I look at the night sky ...
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2answers
1k views

Why light coming from distant stars is not discrete? [duplicate]

Imaging the light racing out from distant sun, as beam of light shoots aways is a circular pattern (spherical actually), remembering that, light comes in photons or packets of energy. so how come is ...
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1answer
28 views

Would not the oscillation of light slow down the wave? [duplicate]

Would not the oscillation of the light wave slow down the wave? Does light travel at "c" of its net position over time, or does it travel at "c" on the wave?
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49 views

Moonlight reflection on ocean [duplicate]

I am trying to explain physically what is happening in the picture below: My gut explanation is that we are observing the reflection of a cone of light emanating from the moon, it explains the form ...
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2answers
52 views

Can lasers cause glare or reflections?

When going to the movie theater I sometimes notice reflections from the projector on my glasses and I find it very annoying. What happens is that the light hits the back of my glasses and i can see a ...
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3answers
607 views

Is the black hole image in false color?

The first-ever image of a black hole released this week was taken with radio telescopes, suggesting that it is a false-color image and doesn't represent what a person would see in reality, or visible ...
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75 views

How does a concave lens form a virtual image?

If rays of light are diverged upon exiting a concave lens, then they have no focal point. The rays completely spread out in random directions. Like diffuse reflection(which does not form an image) So ...
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0answers
21 views

(Color Temperature) How to calculate combined color temperature (kelvin) of two different sources

I have been looking for a while but I can't seem to find any information on this. I would like to figure out the formula to calculate the CCT of two calibrated sources of light relative to their ...
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11 views

Why is the luminous flux in a closed sphere equal when the light bulbs are the same Watt regardless of the radius?

Why is the luminous flux in a closed sphere equal when the light bulbs are the same Watt regardless of the radius ?
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1answer
21 views

Why is luminous intensity dependent on the incident angle?

Why is luminous intensity dependent on the incident angle which hits a surface of a specific area?
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1answer
39 views

Cylindrical Light Waves and how the wave equation changes

My homework asks "Suppose the source was a long thin filament so that cylindrical waves were generated. Describe how your equations would change for this situation." The equations we have that they ...
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1answer
39 views

Does light only mimic water waves, or also the properties of water?

Huygen's Principle compares diffraction to ripples in water. Do the similarities translate to surface tension? The hydrophobic effect?