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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6
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6answers
410 views

Is antumbra part of shadow darker than penumbra part of shadow?

I'm exploring different types of shadows casted by objects. I want to know if antumbra part of a shadow is darker than penumbra part. I've found two misleading pictures on Wikipedia: First: Second: ...
1
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1answer
288 views

Lambert's cosine law

I am learning how to physically render images in computer graphics. I just saw that the area that gets light is given by the Lambert's cosine law. In my head it makes perfect sense the relation but ...
0
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2answers
164 views

Do any other particles get excited(or absorb energy) by photons like electrons?

Electrons get excited to different energy levels when photons of specific frequencies fall on them.But, is there other particles which absorb the energy of the photons?
0
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2answers
86 views

Length of solid part of object shadow

Little background first: I take part in preparing environmental reports for wind turbines/farms and now I'm exploring shadow flickering effect of moving blades. From some sources (in Polish) I got ...
3
votes
3answers
222 views

What electric field vector should I use for modeling unpolarized light?

Regardless of computational cost, light is a kind of electromagnetic wave, so it can be simulated with Maxwell's equations. If we want to simulate light with Maxwell's equations, we need to express ...
1
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2answers
211 views

How to test cutoff frequency of IR filter on camera?

Modern cell phones seems to come with IR filters on their cameras. I want to do an experiment to figure out what wavelengths these filters allow to pass and which they block. How would I go about ...
1
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1answer
865 views

How is light created?

I'm very curious about how light is created. I'm trying to get back to some type of real understanding about why everything on the sub-atomic level vibrates and the implications for the ...
3
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2answers
95 views

Will changing the color of the light source change the apparent brightness on a traffic light?

Let's say you have a traffic light with the well known red, yellow, and green tinted glasses. Setup 1: Each glass has a white light bulb behind it. Setup 2: Each glass has a colored bulb behind it ...
0
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1answer
70 views

is redshift still true if object emitting is not moving away but the observer is

If something is moving away fast it's color would appear redder than its actual color due to phenomenon known as Doppler effect. But what if the object isn't moving but i am moving away faster would ...
-1
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1answer
144 views

How light causes increase in temperature

Temperature is the measure of movements of atoms. So if something is said to have high temperature it means that its atoms are moving fast or have high KE energy. There are basically two ways heat ...
0
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1answer
150 views

When an object casts a shadow, why are there different shades of that shadow?

Let's imagine that there is a lamp on the floor. There is a dice on that same floor casting a shadow from our light source, the lamp. Why is it that there are different shades of the shadow phasing ...
4
votes
2answers
371 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 ...
0
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2answers
172 views

Does light have an unending journey?

When we shine a torch in a room its light travels to the back of the room. What happens to the light of a star ? I dont suppose we can say it continues to travel to the back of the universe as the ...
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3answers
235 views

Color of a substance

A plant with green leaves viewed under red light would appear as which color?
-3
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1answer
76 views

What is the speed photons coming out from headlights of a car running 100 km/h? [duplicate]

And, technically, would the color of the light change at different car speeds?
3
votes
3answers
158 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
votes
3answers
589 views

Real image with converging lens?

I read in a AQA GCSE book that: A real image is formed by the converging lens if the object is further away from the principal focus/focal point. I did this experiment in class: Here is my ...
4
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2answers
263 views

Why do clouds appear black?

I have noticed clouds appearing black during rain. But I don't know what makes clouds to acquire that colour. This phenomenon doesn't appear every rainfall. There has to be distinction to white ...
0
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2answers
125 views

What colour is the Earth?

More specifically, what shade of blue is the earth on average? I want to create an accurate earth-coloured blob in a simulation / presentation. A quick search didn't turn up anything. What I found ...
3
votes
2answers
414 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 ...
3
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0answers
54 views

Two Photon Absorption dependence on Semiconductor Band Gap

It's well known that Two Photon Absorption coefficient is scaling with $E_g^{-3}$. Does anyone know what is the physical reason for this scaling? What is the physical theory behind this mathematics?
10
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3answers
603 views

What causes atoms to have their specific colors?

I understand that light (color) is part of the electromagnetic spectrum, and that it depends on what wavelengths are reflected/absorbed. Though what property of an individual atom gives it its color? ...
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1answer
36 views

Additive Trichromatic Color: Seeking Answer for a Fun Application

I'm not the brightest person and I was wondering if it was possible, in the same way that it's possible to make ink that's visible under UV light, if it's possible to make ink that requires a distinct ...
3
votes
1answer
150 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 ...
0
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2answers
116 views

Length contraction as $v>c$

What would theoretically happen to an observed object's length (let it be a 5 meter line) moving at some speed greater than that of light in a straight path?
0
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2answers
678 views

Is there 100% reflective mirror…i just want one

I have heard there are none right now...but i saw something that said something about 100% reflection. Forgotten completely. sorry. I want it, i think it'd be very amazing to save sunlight in it from ...
2
votes
1answer
159 views

Finding Interstellar Extinction Coefficient

I have the following problem for an astrophysics course: A star is seen through a rather dusty region of space has its brightness dimmed by +1 magnitude/kpc, which makes it seem further away ...
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0answers
91 views

Do atoms and molecules affect light rays

Molecules of air are all around us all the time. If so, during daylight do rays from the sun diffract as it passes through molecules in the air? and if so is this diffraction negligible to be noticed? ...
68
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2answers
2k views

Why is a laserpointer able to “erase” a glow-in-the-dark sticker?

a while ago I tried to charge a glow-in-the-dark sticker using a simple red laser pointer. It was a large sticker, of the type used to mark emergency exits and fire extinguishers here in Germany. I ...
4
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1answer
381 views

Why same formula describing Doppler effect in the case of light in different situations?

I made comparison between Doppler effect in light and sound and one interesting thing that I saw was that in the case of sound there are different formulas to find the apparent frequency in different ...
3
votes
2answers
126 views

Is there any case of total transmission?

When light strikes the interface of two media some light is refracted and some is reflected. But, is there a case where no light is reflected i.e all the light gets passed through the given object. ...
4
votes
2answers
477 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 ...
2
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2answers
313 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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1answer
70 views

speed of light observation

I was on a ship at night travelling parallel to the shore watching a lighthouse beam hitting the concrete sea wall. As the beam hit the wall at ninety degrees and continued to rotate I saw what ...
37
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6answers
3k views

If I am travelling on a car at around 60 km/h, and I shine a light, does that mean that the light is travelling faster than the speed of light?

The title says it all. If I was on a bus at 60 km/h, and I started walking on the bus at a steady pace of 5 km/h, then I'd technically be moving at 65 km/h, right? So my son posed me an interesting ...
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0answers
51 views

Is there any evidence that everyone sees colours the same way? [duplicate]

We all know that the sky is blue. Grass is green. Blood is red. But, how do we know that everyone sees these colours more or less the same? How does one know that my ...
6
votes
1answer
365 views

Why does burning things make them black?

It's not clear to me how burning process can transform a material which was previously capable both of absorbing and emitting photon to one which can only absorb them. I would like to hear an educated ...
9
votes
6answers
7k views

Is “dark clothes for winter, light for summer” relevant?

We are told to wear light clothes in summer as they are better at reflecting sunshine and keeping us cool. And dark clothes absorb sunshine and keep us warm. But is it really relavent? If I buy ...
3
votes
1answer
64 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 ...
0
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1answer
118 views

Why does a street light cast a wavey shimmer across the water (at night)

See image You will have to zoom in. Why is the reflection a wavey one? Could someone explain how this is occurring, to the layman, (with the style of feynman if possible -heh) :)
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3answers
136 views

Quantum mechanics: How do the atoms in an electronic circuit enter a smaller orbit on the filament of an incandescent light bulb?

Bear in mind that this is not a homework question, and I have put together some stuff to work on from below: http://www.doublexscience.org/how-fluorescent-lights-work-quantum-mechanics-in-the-home/ ...
3
votes
1answer
868 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 ...
0
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1answer
90 views

Depolarisation of Light in Optical Fibre

I have a question for which I can't seem to find a solid answer in literature and wondered if anyone could offer advice or reliable references please: How does light depolarise in ...
2
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2answers
81 views

Can contemporary technology simulate the spectrum of a star?

The ability to manipulate light spectra (as in mercury lamps, sodium lamps, infra red) is within the ambit of contemporary technology. Stars are said to be unique in the spectrum they emit ; ...
1
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5answers
455 views

Light-like Interval

In SR, the interval $I$ between two spacetime events is called light-like if $I=0$. Griffiths in his Introduction to Electrodynamics book says that [page 503], If $I=0$ we call the interval ...
3
votes
5answers
276 views

Can light travel slower than the maximum?

First of all, I know that light does indeed travel slower in a medium like air or water, but that's because the photons are bouncing off of the medium's particles and in different directions so the ...
0
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2answers
87 views

The speed of light through space and its effects on black holes

I was curious about a couple of things that don't quite make sense to me: (and probably won't when I get the technical answer, but I'll ask it anywise.) When light travels through space, is its ...
1
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1answer
219 views

Principle of relativity and motion perpendicular to the direction of light beam

consider you are in a train that moves with a speed of $c/4$. A bulb is hanged from the ceiling. A light beam leaves the bulb downward. Exactly under the bulb on the floor is a detector. According to ...
4
votes
2answers
456 views

Does thin film interference (anti-reflective coating) let more light through?

The theory of an anti-reflective coating is that the reflected light off the coating and the reflected light off the substrate is 180 degrees out of phase, causing destructive interference and ...
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1answer
504 views

Resonance Experiment

Today in high school physics class, we performed an experiment on the resonance of sound, with a set up like this... To put it simply, the sound waves are supposed to rebound with the surface of ...