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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12
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1answer
199 views

Sun in front of horizon after sunset; mirage or reflection?

The day before yesterday, I observed sunset while flying over the eastern Mediterranean. After the sun set, it seemed to 'continue' in front of the horizon. I managed to snatch a picture (sorry for ...
3
votes
1answer
63 views

light falling on a completely reflecting friction less mirror

If you had a perfectly reflective mirror whose face was perpendicular to the ground and was kept on a friction less track on the ground, and you shined a flashlight on it, what would happen? Would ...
11
votes
4answers
389 views

Effect of gravity upon light and bagels

According to this question and this web site, photons undergo twice the deflection from gravitational fields as do physical objects. However, the weak equivalence principle states that locally, ...
0
votes
1answer
68 views

Can someone reconcile the Boltzmann transport equation with the Maxwell equations for photons/light?

Having taking courses in both physics and nuclear engineering, I've noticed that the two fields tend to describe photons/light in two different settings. In nuclear engineering, the radiative ...
15
votes
3answers
1k views

Why is the bottom part of a candle flame blue?

What’s the explanation behind the bottom part of a candle flame being blue? I googled hard in vain. I read this. I don’t understand how it’s explained by the emission of excited molecular radicals in ...
0
votes
0answers
28 views

The path that light travels [duplicate]

This is a question that has puzzled me for some time. As a star emits light, the light travels away from the star. If you were to pick any spot on the star and draw a line extending outwards and then ...
-2
votes
1answer
115 views

Experiments to the question : why wet is dark?

How can we prove the explanations for: why clothes get dark when they are wet, by experiments?
0
votes
1answer
104 views

How to transform infrared beam into visible range?

I am looking for an easy method of turning an infrared beam into a visible beam. There are some well-known ways to do it, for example a camera objective, but it that is very big and uncomfortable to ...
4
votes
2answers
117 views

Is there something equivalent to a diode for light?

In electronics a diode is a component allowing current passing in only one direction, and blocking the other side. I'm wondering if something similar exists for visible light or other EM waves, like ...
3
votes
2answers
545 views

Is there anything that could attract and trap a photon?

Is there any particle or anything that could attract and trap light or photon particle? Can anti photon particle attract photons and trap them ?
1
vote
2answers
121 views

Understanding colored shadows [closed]

When I turn on white lights, these chairs cast a shadow. However, when blue LED lights are turned on the shadow turns yellow. Why is this? Is this due to interference of light or is it just an ...
3
votes
2answers
164 views

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 ...
1
vote
2answers
134 views

How does light actually behave?

Senario: I am walking 5 meters/second and have a laser pointer that I shoot a burst of light from perpendicular to to the path I am walking on. Would the light travel perpendicular to the path from ...
0
votes
1answer
50 views

How does gas pressure increase the lifespan of Halogen tungsten lamps in the Halogen Cycle?

I am curious about this passage "Since quartz is very strong, the gas pressure can be higher,[5] which reduces the rate of evaporation of the filament, permitting it to run a higher temperature (and ...
34
votes
8answers
5k views

Will we ever be able to view the past?

By analogy with the sun, whose light is apparently reaching us in 8 minutes, it means that we are only viewing the sun 8 minutes ago when we look up at it. However, what if we were eventually able to ...
0
votes
0answers
105 views

Why do different wavelengths travel at different speeds through a medium? [duplicate]

Someone gave an explanation in another question: "Maxwell's equations predict that in a linear medium with permittivity ϵ and permeability μ, the speed of light in the medium will be v=1/ϵμ. When ...
5
votes
3answers
235 views

How to arrange mirrors so I can't see myself?

If I wanted to surround myself with mirrors how would I need to arrange them so that if I stood in the middle of them I couldn't see myself in any reflection? For simplicity let's just say we only ...
0
votes
1answer
413 views

Infrared Vs Visible Light

Infrared waves are widely used for quick heating objects, but a quick look at electromagnetic spectrum astonished me and raised a question that how come an infrared wave with lower energy compared to ...
56
votes
2answers
11k views

Why don't fluorescent lights produce shadows?

I have watched light sources such as incandescent lamps and other lamp sources; they have always made shadows. But a fluorescent lamp doesn't make any shadow. What is the reason behind the ...
2
votes
1answer
214 views

At what rate does light 'bend' around the surface of the earth?

Since the g force of earth is 9.8 m/s*2 does that mean light 'drops' at that rate as it travels past earth? Or is general relativity a lot more complex than that?
0
votes
3answers
172 views

What is the physical significance of the negative amplitude of a light wave?

I want to understand what is the physical significance of negative amplitude of a light wave? In an ac electrical circuit, I understand that negative amplitude signifies the amplitude measured when ...
1
vote
1answer
35 views

How long will a light bulb work isf the glass shell removed?

How long will a light bulb work if it gets its glass shell removed?
7
votes
2answers
985 views

How do we know the wavelength of colours?

Every site and video I have been on doesn't address it directly.specifically I want to know what is are the experiments we derive these wavelengths from and how do we calculate the wavelengths inspite ...
5
votes
2answers
1k views

Can spectacles converge sunlight to an extent that it burns the eyeball?

I need to know whether wearing spectacles can cause optical harm. I saw a movie where one pair of glasses was placed on table exposed to sunlight, then the sunlight converged and focused to a point ...
3
votes
2answers
2k 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 ...
1
vote
2answers
163 views

Basic rule for diffraction

I'm a high school student. I still don't understand the reflection, diffraction and refraction of light. It seems to me that in concept of quantum physics, reflection is just a process of object ...
2
votes
2answers
192 views

Rainbow reflected on TV screen? (pic attached)

According to wikipedia, A rainbow is an optical and meteorological phenomenon that is caused by reflection, refraction and dispersion of light in water droplets... Given that we require ...
1
vote
1answer
77 views

Possibility of a Dark Star

I think it was a very early notion, pre-black holes, that there may exist a star that was so massive, all of its outgoing light would return to its source. Is this actually possible? Is there an ...
4
votes
1answer
568 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 ...
3
votes
4answers
118 views

Is light amplitude spacial?

In diagrams I often see light waves depicted as little sine waves that travel through space. And often when describing polarizers, the explainer will angle their hand to show the angle of ...
0
votes
0answers
51 views

Polarization modulation

To increase bandwidth, for EM free space communication, could you modulate the polarization, so that, e.g., for a one-meter wavelength radio wave, the polarization could be modulated between vertical ...
0
votes
2answers
136 views

Why does black glass reflect better than white one?

Why does black glass reflect better than white glass? Both of them are glasses, so they reflect light. But why black glass reflects better? See below, shiny black glass.
1
vote
1answer
51 views

Why are LCDs black? [duplicate]

I had a question on LCDs after noticing something interesting about its color. LCDs are black when they aren't used. But when we observe LCDs closely, we see they are made up of red, green, and blue ...
1
vote
2answers
136 views

what is the whitest material?

I saw before a great question on what is the blackest material. Therefore I started wondering, there are many things that look white but in fact absorb light. So what material is truly white? Or, ...
3
votes
3answers
121 views

How to improve the visibility of light without increasing the brightness?

I am not sure whether or not this is the right SE site to post this question on but I'm sure someone will inform me of my mistake soon enough if it is wrong. Basically I am an Electronic Engineer and ...
2
votes
2answers
165 views

Moving electric charges

I just wanted to double-check these three statements, as I'm not entirely sure I understood them completely: 1) A stationary electric charge (let's say a proton) produces electric field. 2) A moving ...
0
votes
1answer
115 views

I want to know why light even moves at all.

Never mind in a vacuum, why and how does light even move at all? What propels it?
1
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0answers
22 views

Does illuminating a conductor with light energy less than its workfunction change the measured conductivity?

For example, does the light absorbed in an exposed metal wire increase the average velocity of the electrons, hence increasing mobility and conductance?
2
votes
1answer
57 views

Intensity of light wave penetrating soft tissue

I'm studying for a medical physics exam and I'm struggling with the following question: Calculate the fraction of energy which penetrates to a depth of 3cm in soft tissue for a beam of light at a ...
1
vote
0answers
30 views

Band of color around a light source [closed]

When a light source, like a phone flash light, is observed in the dark, why is there a band of seven colors observed as a ring around it ?
2
votes
0answers
148 views

Possibility of a free-space hologram

Holograms are real. But they are not what sci-fi calls holograms. From a simple geometric optics standpoint we can see that in order to create the illusion of an object there must be some sort of ...
1
vote
2answers
133 views

Convert normal white light to laser-like light?

Is there a probable device that can convert white light to laser-like light without the need of an electrical stage in-between? I'm thinking of something along this level. A very precise filter and ...
3
votes
1answer
66 views

What are the common points between physical optics and geometric optics? [closed]

I am trying to write a paper about light, I want to discuss the two way of studying light, the physical/wave optics and the geometric/ray optics, but I want to write a general introduction about them, ...
0
votes
0answers
26 views

What does the refractive index depend on? [duplicate]

I've always thought refractive index is dependent on the density of the material. The more denser, the more refraction. But kerosene whose density is higher than water has refractive index less than ...
1
vote
2answers
40 views

What is the maximum light difference for one to be able to see into or out of a building and equally discern objects? [closed]

In this question I am referring to the physics behind not being able to discern objects outside when in a lit room, even though you would be able to discern them if you were outside, even though when ...
0
votes
1answer
60 views

Why EM waves with long wave length traveles long distance cmpared to EM waves of smaller wave length? [closed]

Most of the times i was told with an example that police uses red light because they travel large distance than compared to blue or green or other wave lengths ? ...
1
vote
2answers
123 views

Why do I see things better when they're reflected through my iphone screen?

Sometimes looking at a screen for too long hurts. This happens to me when I use my computer or smartphone for too many hours, and my eyes become tired and weak. Lately I noticed that if, instead of ...
2
votes
2answers
427 views

If photons have no (rest) mass, why would black holes attract light? [duplicate]

I was told that photons have no (rest) mass. However I thought that black holes are called "black" because no light can go escape the gravity force in their vicinity. I somehow think that, if light is ...
3
votes
2answers
316 views

How we see laser light if it travels in a straight path? [duplicate]

Light travels in straight path, and our eyes detects an object's reflected light then we see the object. So if laser light is going in a straight path, how come we can see laser light?
0
votes
1answer
32 views

Duality in Electromagnetic Spectrum

Is visible light the only portion of the electromagnetic spectrum that exhibits particle/wave duality? If so, how/why do other frequencies (i.e. radio) behave as waves?