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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Why do we see brown light?

While researching about lasers (it's my hobby), it suddenly hit me: there are lasers for every color of the visible spectrum, but there are no brown lasers. Brown isn't even on the rainbow. How is it ...
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1answer
270 views

Inside a spherical mirror

imagine standing inside a sphere composed entirely of mirror surface; what does this look like? inside is lit by an invisible light source if each point encounters a reflection of itself, what is ...
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2answers
95 views

reflection of light and the uncertainty principle

I've heard that light reflects the same angle that it falls and so if we know the position of photon (the spot where it hits the surface) and the direction of where it shall go - that's violation of ...
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2answers
80 views

Why lasers and not light? [closed]

Some laser applications consist simply concentrating light into a small spot (e.g., image projection, welding, cutting, etc.). Why are lasers used instead of a simpler light source?
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276 views

Why do two beams of light pass through one another without interacting?

Why is it that if I have two torches, each shining rays in perpendicular directions at perpendicular screens, such that the beams cross, then the images on the respective screens are independent of ...
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1answer
103 views

Is it possible to produce coherent light with a thermal source? [closed]

Coherent light means monochromatic light and alle waves have the same phase difference. This is given for laser, where the resonator is a potential box and the outgoing waves have the same phase ...
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1answer
79 views

What happens if light is trapped between two points?

The image can explain my question In the image light is clearly trapped.Even if the mirror absorbs energy the light is continously being added, will there be enough force to break the mirror?
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2answers
336 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 ...
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2answers
223 views

Why does light from a laser end up in a concentrated spot?

I've heard from several people that photons will always take the past of least action while travelling, so why does laser light projected on a surface appear concentrated to a single spot when ...
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5answers
419 views

Why is microwave better than visible light for point to point data communication?

In the electromagnetic spectrum, it appears that the shorter the wave length, the better the bandwidth due to higher frequency. Some communication systems utilize microwave to transmit data to offer ...
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1answer
142 views

How to get the direction of bending light?

When light passes from a more dense to a less dense substance, (for example passing from water into air), the light is refracted (or bent) away from the normal. My question, is there any ...
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1answer
69 views

Photons “rate of fire”

I'm not sure if this makes any sense but, do photons "discharge" from a source at an infinite rate?
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167 views

Redshift of a reflected photon from a solar sail

Can someone help me understand my mistake here? I'm thinking of a photon travelling with momentum $p=h/\lambda$ which reflects off a solar sail of mass $m$ travelling with momentum $p_0$ in the same ...
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1answer
82 views

What does the size of an object have to do with it's color?

Stephen Hawking mentions in his book 'A Brief History of Time' that quarks are much smaller than the wavelength of visible light so they do not have any color in the normal sense. What exactly does ...
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1answer
192 views

What does adding a visible light blocking IR filter do with heat?

Lets say I have a strong halogen light source which has a lot of IR radiation (e.g. a construction lamp). If I change the transparent front glass from the enclosure with a IR filter that blocks ...
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2answers
87 views

Does a light wave that has been cancelled by another light wave continue traveling forward?

I imagine that if a light wave is cancelled out by another light wave, it would still continue to exist as a photon that is traveling at the speed of light--only without a wavelength. Would it behave ...
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1answer
243 views

Physics and Skin Color: What differences do physicists observe between different skin colors?

I majored in social sciences, so I haven't taken a science class since 1999, so forgive me if I don't ask this right. What difference would skin color make from a physics perspective? Would there be ...
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1answer
485 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 ...
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2answers
110 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 ...
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2answers
7k views

what is the best way to collimate light emitted by a led?

I'm new to this forum. This is half a question, half a challenge. And it's more engineering then physics but I thought I might get good insights from a physics forum. I would like to cure a UV ...
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1answer
1k views

Visible light through a single-mode optical fiber?

If I understand things correctly, the optical fibers used for (long-range) data transmissions are generally single-mode fibers, transmitting light in the 1300-1500 nm spectrum. Now, could such a ...
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1answer
5k views

What causes refraction of visible light? [duplicate]

Refraction is the bending of a wave when it enters a medium where its speed is different. The refraction of light when it passes from a fast medium to a slow medium bends the light ray toward the ...
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2answers
1k views

Polarized sunglasses: should the axes in both lenses be parallel?

See the pictures below. A pair of sunglasses I recently purchased has the polarization axis in one lens offset about 20 degrees (by eyeball estimation) from the other. I don't have much experience ...
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1answer
2k views

Light dispersion in water

Simple question: Water is clearly not disspersive if we have it, for example, in a glass of water. We don't see the rainbow through a glass of water. However drops of water disperse light in the ...
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2answers
92 views

Photon's multiple frequencies by Fourier

Since any source of light will have a finite duration, the light emited won't have a particular frecuency. It will be a sum of different frequencies (infinite, I think) if we apply Fourier's series ...
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2answers
594 views

Why can't some light ever reach earth? [duplicate]

Note: I'm a layman in physics. Excuse me if this question is a duplicate, I lack the knowledge in technical terms to find the answer to this by research (I've tried). Let's suppose there's a star ...
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1answer
1k views

Factors affecting the size of a shadow

What factors affects the size of a shadow and how would you derive the diameter of a shadow of a circular object on a flat screen?
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1answer
115 views

Relationship between photon polarization and photon angular momentum

What direction is the angular momentum of right hand polarized light points to? Is it vertical to its propagating direction? I want to recognize this in quantum theory.
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136 views

Speed and transparency of light

I have been puzzled with a fact that as an object moves faster, it ceases its property of opacity. I mean to say that as an object moves faster we can see right through it (more clearly than in a ...
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1answer
257 views

william herschel discovering infrared problem

when william herschel conducted the experiment of separating white light with a prism and measuring the different colors, he put a thermometer past the red color as a control finding it to pick up the ...
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1answer
838 views

Resistance of Light Dependent Resistor (LDR)

Is there a mathematical expression relating the resistance of Light Dependent Resistor (LDR) with light intensity?
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1answer
643 views

How can you test what color different people perceive? [closed]

If I would show someone a yellow object and ask them, "is this object yellow?" That person would say "yes". But I could never know if my perception of the color yellow is the same as that other ...
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2answers
609 views

Building a LED lamp, which is the brightest? 3 LEDs of 2500 mcd or 1 LED of 6000 mcd?

I want to build the brightest lamp, for it to be seen at daylight, should I use 3 2500 mcd LEDs or 1 6000 mcd? And also Why?
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1answer
156 views

Where do the high order rainbows appear?

This site shows locations of the high order rainbows up to sixth order. My thought is that, There should be even higher order bows like 7th, 8th, etc. (Though they would be practically impossible to ...
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1answer
109 views

What would the spectral distribution of a greenbody look like?

Suppose you had a body that behaved like a blackbody for all wavelengths except some range that we would call "green". For those wavelengths it reflects all radiation incident upon it. Am I just ...
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1answer
7k views

Why are umbrellas black?

Why are umbrellas specifically in black? Of course we do have colored ones, but black is the majority. Is there any scientific reason behind it?
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2answers
452 views

Light pollution calculation using camera

Is it possible to calculate light pollution values using camera (analyzing camera feed) integrated in new smartphones (8 Mpx camera) but with pretty decent accuracy? Or that is only possible with ...
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3answers
2k views

Conversion formula from spectrophotometer readings to any standard color space profile?

I have readings of colors from a spectrophotometer that records across the human visible color spectrum 390nm to 790nm intervals. I'd like to convert this into any color space, could be CIE XYZ, HSL, ...
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1answer
56 views

Diffraction wavelength relationship [on hold]

This question appears somewhat similar to other questions asking about why wavelength affects diffraction (a concept which I'm still not 100% sure on...) however my query is different and not answered ...
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1answer
29 views

How does sunlight undergo interference as shown in the video?

As far as I know, for interference to happen in a double-slit experiment, the light source should be coherent and monochromatic. If that is the case then how come sunlight undergo interference and ...
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2answers
39 views

Double slit with opposite circular polarizers

Let's say I'll send linearly polarized light onto double slit but in front of one slit I'll have quarter wave plate and before the other I'll have 3/4th wave plate (half+quarter? minus quarter?) ...
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1answer
57 views

How are professional laser shows done [closed]

How are professional laser shows done ? I need an explanation of the phenomenon of a laser visible in mid air ,(NOT THE APPARATUS USED which means I don't want the engineering aspect of it,I only want ...
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2answers
87 views

Can light projection on a wall travel faster than the speed of light? [duplicate]

If I project a flashlight beam on a wall and turn the source, the projection (as seen on the wall) is seen moving along the direction of the turn with some speed. If I have projected it on a gigantic ...
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1answer
48 views

I would like to know if violet bends the least or red [closed]

I had read that violet bends the least. But most of the webpages state that red bends the least. I would like to know why it is so.
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2answers
79 views

How come lenses alter the path of photons?

From what I know, photons are theorized particles and believed to be massless (just energy) and travel at the speed of light. How come a lens, which is an object made of atoms, can bend a light path? ...
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1answer
26 views

How does light behave after experiencing fully destructive interference, as in an interferometer?

I'm thinking about a laser interferometer like the one used in LIGO. Here's the basic layout (from Wikipedia - Interferometry): My understanding is that the half of the light that is reflected by ...
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1answer
15 views

illuminance on a slope plane

I am trying to understand the illuminance from an extended source(sky dome) on an inclined plane. The article I am reading has beautifully explained it. Yet I don't understand the angles and boundary ...
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1answer
94 views

How physicists explained straight line propagation of Light thinking of light as wave? [duplicate]

To explain the fact that light travels in a straight line assuming light as a wave physicist said that it has small wavelength. So how does the small wavelength explains the property?
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1answer
39 views

Is illuminance defined only on a surface normal to the flux?

Assuming on the below image the source is a point source, I can understand that since the light flux falls on dA is the same within the solid angle and since the intensity I = Φ/dω and E = Φ/dA it can ...
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1answer
54 views

Implication of Relativity [duplicate]

According to relativity, no useful matter can travel faster than light. Suppose that your are a light beam travelling. Now you have a parallel light beam travelling beside you. Suppose you look at the ...