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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'ting' 'ting' sound from a tube-light?

Whenever I light up a tube-light it makes 'ting' 'ting' sound every-time it blinks. I am talking about this tube-light Why is it so? I think its because of sparking(inside glass tube) ...
3
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3answers
170 views

Do electromagnetic waves have endpoints?

When learning about electromagnetic waves at school we never talked about any endpoints as we did with standing waves, so I assumed that light has an endless length, but that doesn't make sense. So my ...
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2answers
466 views

Incorrect IR temperature reading on stainless steel?

Using a Fluke 62 Mini Infrared Thermometer today on a stainless steel pipe with coolant I noticed that it gives incorrect temperature readings. There is a temperature sensor inside the coolant ...
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1answer
859 views

Why do most metals appear silver in color with gold being an exception from a scattering and EM viewpoint?

Related: Why are most metals gray/silver? After reading Johannes’ impressive answer to Ali Abbasinasab question of why do most metals appear silver in color with the exception of gold (and copper), ...
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2answers
103 views

Would it be possible to build a Solar Panel Etalon?

Since, on average, 1/3 of all sunlight that hits a solar panel is reflected, wouldn't it be possible to set up some kind of etalon system where the reflected light is then absorbed by another solar ...
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2answers
643 views

Is light brightness subjective or can it be quantified?

What is the relationship between brightness perception and physical properties of light, such as light intensity?
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1answer
124 views

What the name of the evacuated glass gadget with black and white vanes that turn when a light is applied?

I remember a glass device my physics teacher had at high school which Contained some vanes mounted somehow on a vertical axis, which were all black on one side and white on the other Was in a ...
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5answers
214 views

Light refraction and causality

One way how to look at refraction by a dielectric medium like water or glass is that (phase) velocity of light decreases because it is the wavelength rather than the frequency of the light which ...
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6answers
6k views

Limit of human eye flicker perception?

I am designing a LED dimmer using software-controlled Pulse Width Modulation, and want to know the minimum PWM frequency that I must reach to make that LED dimming method indistinguishable from ...
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2answers
73 views

Did Newton argue that particles speed up when entering a more dense medium?

Statement: Newton argued that particles speed up as they travel from air into a dense, transparent object, such as glass. From this source, I gather that he did argue that the light particles ...
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1answer
87 views

Would white light waves act as same as monochromatic waves in double slit experiment?

Would white light waves act as same as monochromatic waves in double slit experiment? If not, what pattern would be seen on the screen?
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2answers
359 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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1answer
199 views

Why does the Sun turn red near sunset?

At daytime the Sun's light is yellowish if not near white. Why when the Sun starts to go down that it's light turn more red. I don't think the earth's rotation is so rapid to cause a red shift. Why ...
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1answer
108 views

Polarisation of light is a wave concept or applicable to photons as well?

I have a very fundamental question. We explain polarisation of light assuming wave nature of light. Is it still valid if we assume light as photons? Or in other words, polarisation is a wave concept ...
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1answer
88 views

When was it established light travels forever?

The range of electromagnetic radiation is indefinite. When was that established? Doesn't Hubble's limit have an effect?
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1answer
715 views

Didn't Newton's Corpuscular theory fail to explain reflection?

In 1637 Descartes gave the corpuscular model of light and derived Snell's law. This Corpuscular model of light was further developed by Isaac Newton in his famous book entitled OPTICKS and because of ...
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1answer
175 views

Why does a light wave invert at a boundary with greater index of refraction?

Is there a reason why a EM wave reflects invertedly when it meets a boundary point with a greater index of refraction. In the case of ropes, if remember correctly, the reason why it inverts is to ...
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1answer
939 views

How far can the human eye see? Any ending point or infinite?

How far can the naked human eye see if unobstructed? (straight ahead on perfectly flat land). Is there a stopping point or is it infinite when you look in the sky? Is there any situation that the ...
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2answers
476 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 ...
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2answers
163 views

why does a mirror show what is in front of it?

the only answer I can think of is that light is reflected from the objects in front of the mirror (visible color) and then reflects again off of the mirror to our eye, but im not quite satified with ...
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1answer
86 views

Looking for a resource that explains all colors and shapes of stars and galaxies

I've been looking at some of the astronomy pictures of the day from NASA. They all have content that is indicative of certain situations or events. Supernovas have the scattered lines look, new stars ...
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1answer
204 views

Why is the shadow of earth red?

Reading this article about the forthcoming eclipse on December 10th, I noticed mention that the moon passes through the red shadow of Earth; I'd always held the impression that a shadow is universally ...
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2answers
979 views

Propagation of light in transparent media: absorption and reemission or scattering?

In the two Phys.SE questions What is the mechanism behind the slowdown of light/photons in a transparent medium? and Why glass is transparent? transparent media were discussed. But I'd like to clarify ...
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1answer
50 views

Can unpolarized light be created from polarized light?

I have a question regarding this topic. According Stokes Parameters theory, unpolarized light could be described as a superposition of two independent beams of equal intensity and orthogonal ...
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1answer
98 views

Why are reflected objects blurry?

While this may seems like a strange question, I'll try to explain it the best I can. Like 75% of Americans, I wear glasses and contacts to correct my worsening vision. I'm not far sighted so objects ...
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2answers
111 views

The speed of light as it approaches a massive body

No matter how fast you go, you will aways perceive the speed of light as constant. Taking that as a fact, the special relativity theory was formulated. Now, for what I understand about general ...
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2answers
126 views

Why does the colour wheel wrap around?

Red colour bares 430-480THz and Violet bares 670-750THz according to Wikipedia. What frequencies are the colours between red and violet? Will they be higher than red? or lower than violet? What ...
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1answer
154 views

What determines the form of the intensity curves in Laser-Induced Fluorescence (LIF) measurements?

What determines the form of the intensity spectra of different particle species in Laser-Induced Fluorescence (LIF) measurements? See e.g. I figure that bigger particles have more ways to get ...
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2answers
136 views

Colors of light

White light is always said to contain all the different wavelengths of light. Why, then, can we 'make' new colors simply by adding wavelengths? Is it just a matter of our perception, that, when two ...
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1answer
382 views

Is there a simple model explaining Faraday effect?

I find magneto-optical effects fascinating, and especially the Faraday effect. But most sources only give a phenomenological description, while I want a deeper explanation of its mechanism. Is there a ...
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1answer
512 views

How to set up a very simple experiment in optics?

This might come across as a very rudimentary question. My fundamentals of Optics are weak. In the optics chapter of my physics text book I saw diagrams each depicting an object on the left and a lens ...
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1answer
430 views

simple test/measurement to quantify water opacity

I am performing some measurements on liquid surfaces and I want to quantify how these mesures depend on the liquid opacity by performing it with different concentrations of colorant. To allow ...
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1answer
376 views

What are the coloured bands in this “Pale Blue Dot” picture?

You can see Earth in the right most band in this image: What are these bands doing in space?! Can somebody please explain the coloured bands in this image?
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1answer
310 views

Lunar twilight and sixth magnitude stars

Summary: when the Moon is x degrees below the horizon, it interferes with stargazing the same as astronomical twilight would. What is x (as a function of the Moon's phase)? We define civil, ...
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1answer
97 views

A mirror in the sky to look at past Earth

Earth reflects light from Sun into Space; are there any "mirror like" objects which reflect back to Earth this light? Has anyone been able to use this method to recover some information on how was the ...
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1answer
107 views

Why do we see the sun's light color different from the moon's light color?

Why do we see the color of the sun's light as red or orange, while we see the moon's light as white, although it's reflected from the sun?
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2answers
302 views

Is the frequency/wavelength of light modified when multiple light sources are combined?

Let's say I light a wall with two spotlights: One red and one green one. Where they overlap, I'll see a yellow area at the wall. My question is, whether this is caused by an modification of the ...
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2answers
160 views

What is the energy distribution of light if it has an infinite length?

What is the energy distribution of light if it has an infinite length? I have read in one of the answers here on phys.SE that light has actually an infinite length. But then what is the energy ...
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2answers
46 views

How should I interpret an article about light being slowed and compressed?

I've found an article describing a method that allowed the light to be "slowed and compressed"... That sounds really strange, which made me google a lot and find this PDF document. However for me, ...
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1answer
205 views

Radio vs optical telescope imaging

As I understand, the visible light from an optical telescope is focused on a sensor which correlates light exposure to an electrical voltage, which is then converted to an image. A single antenna ...
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1answer
66 views

How far can diffused undersea light travel and still be perceived by the human eye?

Example: If one SCUBA diver looks past another SCUBA diver horizontally into negative space, how far away is the most distant emission of 'blue' light waves? Consider the sight angle in question to ...
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3answers
2k views

Seeing colors: photons vs waves

As an atmospheric physics major I am familiar with electromagnetic radiation in the atmosphere and what dictates what wavelength objects will emit at. When observing radiation in the atmosphere it is ...
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2answers
137 views

Decomposing light into frequency spectrum

Light hits a charge coupled element. The wavelength of the light somehow is translated into a color picture. Where can I learn about methods (algorithms) to decompose light hitting a CCD into ...
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3answers
235 views

Question on Radiance equation

The radiance equation is $$ L = \frac{d}{dA} \frac{2(\phi)}{dW cos(\theta)} (watt/srm^2) $$ where $\phi$ is the flux. I am thinking, should not be the cosine term on the numerator instead of the ...
3
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1answer
127 views

Angle of rays leaving a light source

I'm working on ray tracing and I'm trying to understand the impact of the angle at which a light-path intersects the surface of a light source on the amount of light that source delivers to the path ...
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3answers
2k views

formula for transparency of very thin film of metal

Is there formula that gives transparency of very thin film of given metal (tens of nanometers) to the visible light/light of given wavelength ? Which properties of metals are needed for the formula ? ...
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1answer
50 views

How do you transform between theoretical Hertzsprung-Russell Diagrams and Colour-Magnitude Diagrams?

When discussing stars, theorists tend to use effective temperature $T_\text{eff}$ and luminosity $L$ (on logarithmic scales). Observers, on the other hand, usually talk about observed colours and ...
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2answers
1k views

Are Colors Emitted at Specific Temperatures?

There are quite a few nagging questions I have been having over the years, I do not require a full explanation, just some guidance in my assumptions and pointers if I am very wrong. My basic ...
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3answers
550 views

Does the wavelength always decrease in a medium?

I was studying a GRE Physics Test problem where optical light with a wavelength of 500 nm travels through a gas with refractive index $n$. If we look at the equations for wave motion and index ...
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1answer
35 views

Is it possible to improve the efficacy of light bulbs with a semipermeable mirror? (The greenhouse bulb)

Let us imagine that there exists a material that reflects infrared radiation, but is transparent for visible light. Could we take an incandescent bulb and add this material to the inner surface of the ...