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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2answers
48 views

Does any substance possess the property color? [on hold]

A substance possess color according to the color which it reflects. Such as a leaf is green in color because it reflects green. When there is no light, leaf may appear black in color. So is there a ...
0
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0answers
39 views

What is the age of the Universe from the big-bang light perspective?

What is the age of the Universe from the big-bang light perspective? We all agree that the universe is around 14 billion years, from the perspective of a hypothetical observer moving in a galaxy, ...
16
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4answers
2k views

When photons reach us, what exactly is happening to us and to that photon?

I'm new to physics and am just going through some of the free online classes at World Science U, and after watching this video on the nature of the speed of light and its constancy, a question came to ...
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1answer
21 views

Why the crest of water absorb more light than the trough of water?

I have done my experiment using water ripple to study the behavior of waves. I know that the crest will absorb more light than the trough so that the image created on the white paper sheet appeared to ...
0
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0answers
23 views

How do RGB colors work? [duplicate]

They say that all colors can be formed by mixing Red, Green, and Blue appropriately. Is it true? Isn't the Fourier basis infinite dimensional? Or does it turn out to be the case that only three ...
1
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4answers
81 views

Can't virtual images be put on a screen?

Apparently the plane mirror makes virtual images, and virtual images cannot be projected onto a screen. If you look below, it is? If the eye is basically a screen of rods and cones, then everything ...
1
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3answers
51 views

Do atoms of a surface excite to reflect the light?

How do surfaces reflect certain colours and absorb the others?
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1answer
26 views

Calculating the distance between Detector and Double Slit

I have a little problem that is kind of confusing me at the moment. The following task: Light of the wavelength $\lambda = 500nm$ hits a double slit whose distance is $a = 30\mu m$. Each is $a = ...
2
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3answers
64 views

Why can colors be mixed? [duplicate]

We can combine colored light, creating other colors, at least in terms of visual perception. But how it the result physically "a different color" - if it is at all? Or is all this not a physical ...
0
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2answers
46 views

How camera flash can send information

Nikon have CLS a system that allow to trigger one flash with other flash. I don't know how exactly it work from user point of view, I think that one flash (in command mode) can send information like ...
1
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1answer
58 views

How car headlight works?

There are two headlight of car. One having a light bulb between two concave mirrors (one mirror behind and other infront of bulb), and the other type of light only have one concave mirror behind the ...
-2
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1answer
44 views

About light waves [closed]

I read about the Michelson-Morley experiment (forgive spelling) showing Ether as an unnecessary concept for what might have been a medium for light waves. What if space-time is 'saturated' with so ...
5
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2answers
183 views

Which solution to the electromagnetic wave equation is the most accurate model of monochromatic light?

When a photon is modeled as a monochromatic electromagnetic wave its electric and magnetic components are usually taken to be sine waves (for example here ...
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1answer
37 views

How do projectors work?

So, objects are certain colors because they are absorbing every color except for that one. So why is it that if I take a projector and project a blue image on a red wall, the red wall still reflects ...
0
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1answer
32 views

Visual Fields testing: Decibels of sensitivity - meaning

Automated Visual Field test measures the patient light sensitivity in decibels. Questions: If one point has sensitivity of 30 decibels and another point has sensitivity of 27 decibels does it mean ...
1
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1answer
21 views

galaxies fading away after time [duplicate]

Dark energy is constantly pulling all objects away from each other with increasing speed. This in turn causes a red-shift of the light from the most distant object where this effect is most profound. ...
0
votes
1answer
19 views

Why do the RGB gamut vertexes not intersect the edges of human vision on the CIExy plot?

As I understand, the CIExy graphic maps "greenness", or rather middle-wavelengthness, to the Y axis and "redness", or rather long-wavelengtsness, to the X axis. The trapping used to reduce the 3d ...
0
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0answers
38 views

Light emanating from finger tips?

My little nephew on two occasions (when he was 4 now 6) said he saw light rays emanating from his fingers. His father said this is true and that there is physics behind it. I have searched the ...
0
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0answers
20 views

What's the proof that the polarization occur s to the electric field of the light? [duplicate]

What's the proof of the light polarization that it happens to the electric field and not the magnetic field? How did Malus discover that the light is polarized although he didn't see the waves ...
1
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2answers
68 views

Why doesn't the magnetic field polarize when polarizing light?

If the magnetic field doesn't polarize does it follow the electric field path of propagation? or does it vanish?
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0answers
77 views

Photons and Black holes

How many photons in one Planck volume would it take to form a tiny black hole? A photon doesn't have mass but it does have energy, $1.0101 \times 10^{-37}$ Joule for red $650$ nm wavelength light if ...
5
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2answers
146 views

Why must an integrating sphere be a sphere?

Why must an integrating sphere be a sphere? Why can't it be an integrating cube? What is the difference? Could I use a cube to measure total illuminance like an integrating sphere does?
5
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4answers
111 views

Question about the wave nature of light

I quote from my textbook, " Consider two vertical slits S1 and S2 placed parallel to each other, and a string is passed through them. The end B is fixed and A is given jerks perpendicular to its ...
1
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5answers
88 views

If you shoot a light beam behind the event horizon of a black hole, what happens to the light?

I have a couple of questions about light here, and sorry of they are silly.. So since anything that goes beyond the event horizon can't go out, so what if a light beam was pointed somewhere behind ...
1
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1answer
34 views

Light and Prisms

If you matched the yellow light of one prism to that of the green light of another prism, say through a thin glass pane, what would be the resulting color?
2
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2answers
45 views

How is the image in a mirror created without a lens or pinhole?

How is the image in a mirror created without a lens or pinhole? From every point in the world there are infinitely many rays going out. How come the image on a mirror is ok, when there is no pinhole ...
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2answers
32 views

How is the image in a mirror created? Are there infinitely many light rays?

How is the image in a mirror created? Are there infinitely many light rays? My motivation for the question is from image processing. We work with images as discrete 2D functions, as matrices. Spatial ...
3
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1answer
25 views

How is barometric light porduced?

A shaken sealed glass tube containing liquid mercury in a dark room will glow. This has been know since the 17th century and is called barometric light. How does the addition of potassium ...
2
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3answers
69 views

Does Light Ever Cease Once Created

I was reading an article on Huffington Post (link to article) about the Multiverse theory. In the article it said this: The big news last week came from the Background Imaging of Cosmic ...
2
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2answers
71 views

Calculating the coherence length from a spectrum

I have measured the spectrum of the LED in my interferometry set-up, and now I want to calculate the coherence length from it. A commonly found formula is $l_{coh} = \frac{c}{\Delta f}$, sometimes ...
39
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4answers
3k views

Why is water clear?

Water appears transparent to visible light, yet most other objects are opaque. Why is that? Is there an explanation why water appears transparent? Is water transparent at all wavelengths, or are ...
0
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0answers
12 views

Transmissivity of Liquid Crystals in the near-infrared range

The gist of my query is in the title. I have been searching for papers and studies that could provide transmission curves (in nematic liquid crystals) across the visible to near-IR range (or from ...
1
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0answers
48 views

Why color of dress changes when water falls? [duplicate]

When you drop water to dress actually the color changes, that is the color of dress becomes dark, but when you add water to color, for example water color or poster color it becomes light. Why is it ...
1
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1answer
61 views

Does the transmission axis matter for sending polarized light through polarized glass?

If I have polarized light and I send through only one polarized glass plane, does the transmission axis matter, or will the intensity be halved no matter what.
0
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1answer
41 views

Can relativistic momentum (photons) be used as propulsion for 'free' after the initial generation?

In discussing this question about propelling a spacecraft with photons and their relativistic momentum, the author asked that I restate my comment as another question. If photons can really be used ...
1
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1answer
70 views

Is every electromagnetic radiation considered “light”?

Somebody mentioned on Freenode chatroom for physics that All Electromagnetic Radiation are delivered in form of Photons not just light. Is it true? Does that mean if we get a THF electrical ...
3
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7answers
541 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 ...
3
votes
2answers
62 views

Squinting at light sources

I am sure it's just your eyelashes creating a filtering effects, but if you look a a bright(ish) light source such as a lightbulb while squinting, if looks like you are seeing straight light rays ...
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0answers
47 views

How to demonstrate total internal reflection?

How can we demonstrate total internal reflection practically to explain it clearly?
1
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1answer
33 views

Does a high energy photon experience deceleration or direction-change when it impinge into water or something due to the change of refraction index?

Wave experiences refraction when it propagates into another medium which has different refraction index. Lights surely does experience refraction at the border of mediums which have different ...
7
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7answers
855 views

Why can't we have a wave of particles?

I understand the nature of light can be complex and has extensive theories/experimental data. We hear light can be both a wave and particle, so why can't it be both, a wave of particles?
0
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3answers
58 views

Does light color change when refracting? [duplicate]

When light refracts from a medium to a second one, its frequency stays the same, and its wavelength changes. If this is true, why we see the refracted light ray's colour is the same as the incident ...
0
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0answers
8 views

Dangerous levels of ozone from combined UVB lamps?

I have a reptil UVB lamp in my room, and a de-humidifier that uses a UV lamp to clean the air passing through it. Honestly since I got it working (the lamp was dead at first) my room is mold free. I ...
0
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0answers
30 views

How do cathode ray tubes (CRT) synthesize colours?

I just read about how LCD displays were based only on black&white contrasts, and only colour filters on each subpixel generated the colour of a pixel. However, how does that happen for a CRT? Is ...
2
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2answers
29 views

Is every ordinary coloured transparent paper an optical filter?

Can any red coloured transparent paper be used as an optical filter that only allows red colours through it?
1
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1answer
51 views

Red color has largest wavelenght and violet minimum (in the range of visible light). then why does violet light appears reddish? RED + BLUE = VIOLET [duplicate]

My question is simple. Green light is more similar to red light than violet, then why is violet reddish and green not? in the language of frequencies and wavelengths, red and violet should contrast ...
1
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0answers
26 views

Dispersion in a rectangular prism

Why are the colours visible only at the fringes of the light refracted through a rectangular prism?
0
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0answers
16 views

What is the perceived color of a D-illuminant?

I am implementing a software that simulates the color of the sky. To do this, I use a model that takes as input the sun position and returns the Yxy components of a D-illuminant for each point of the ...
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1answer
49 views

Human and Ultraviolet light

As I know, ultraviolet light can be created from burning something at high temperature. So I have a question: Can a human body become a source of ultraviolet light at high temperature? If the answer ...
1
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1answer
95 views

Refractive Index formula for denser to rarer medium

I learnt that the formula for refractive index when light travels from rarer to denser medium is (sin i / sin r) where i = angle of incidence r = angle of refraction Is the same formula used for ...