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.

learn more… | top users | synonyms (3)

7
votes
1answer
5k views

What is the meaning of this “let there be light” joke?

Someone across the restaurant is wearing this shirt, and I certainly don't get it. Update Related: What does this quote about the four dimensional divergence of an antisymmetric tensor mean?
7
votes
2answers
981 views

Could an oscillator at a high enough frequency produce light instead of radio waves?

Considering that light is in the 400-800 THz range, if you had an electrical oscillator that ran at that frequency connected to an aerial of some sort, would the antenna emit visible light, in the ...
7
votes
3answers
5k views

How is temperature related to color?

I spent some time studying about temperatures and color of objects. It turns out that as we heat something it turns to red, then yellowish white and if we heat it more it turns to bluish-white. Like ...
7
votes
5answers
8k views

Is it (theoretically) physically possible to project an image into thin air?

Is there some law of physics that strictly prohibits the projection of 2D or 3D images into thin air (such as holograms in movies) or is a solution to achieve this still up for grabs by an eventual ...
7
votes
1answer
722 views

Huygens wave theory not applicable to lasers or parallel beams of light?

According to Huygens wave theory, every point on a wavefront acts as a secondary source of waves. Using this principle we can never have pretty narrow parallel beams of light right? Like lasers? ...
7
votes
2answers
4k views

Why is getting a tan in the evening less likely than getting a tan in the morning?

When I was young I read one book in which is written that you get more tan on the morning than on evening even light angle from Sun to Earth is the same. Don't remember exact reason, I think because ...
7
votes
3answers
2k views

What determines the apparent radius of the rainbow?

Let's say I know how to compute the apparent radius of a rainbow from the viewpoint of the observer: take a photo of the scene, measure the distance to a known reference object, and its dimensions. ...
7
votes
2answers
976 views

Is it possible to have solid light? [closed]

Is it possible to have solid light? If so, what would it be like?
7
votes
2answers
1k views

Slowing down light in an opaque crystal for a whole minute

I just read about a team of physicists at the University of Darmstadt, Germany, that managed to completely slow down a beam of light that traveled through an opaque crystal (article here). How is it ...
7
votes
3answers
1k views

Triple slit experiment

If the experiment is done with single photons and a "detector" at one of the slits the interference pattern breaks down. What happens if three slits are used with single photons and a "detector" at, ...
7
votes
2answers
1k views

Calculating the illumination of the moon

I am trying to find a formula that will enable me to calculate the illumination of the moon down to one thousandth of a percent, given that the Gregorian year, month, day, and hour is known. Can ...
7
votes
2answers
247 views

Bending of light - photon's inertia instead of mass

Using classical mechanics, the formula for gravitational attraction is $$F = G\frac{m_1m_2}{r^2}.$$ This formula does not work for photons, and we need to use Einstein's theory of gravity to ...
7
votes
1answer
227 views

Is Huygen's Principle Axiomatic?

Is Huygens Principle just a fundamental way to understand light? It always seemed to me that it was somehow "derived" or that it should be-but is it simply a well-founded theory?
7
votes
1answer
289 views

Why does separating plastic from a cough drop create flashes?

I was tearing open individually-wrapped cough drops in the dark, and noticed that when I pulled apart two adhesive-joined pieces of silvery plastic film, small flashes of light were produced. It was ...
7
votes
4answers
16k views

What common materials absorb most infrared light?

I'm competing in a simple robotics competition where most of the participants use reflected infrared light to detect their opponent. I'd like to make my own robot as difficult to see as possible. What ...
7
votes
2answers
254 views

Is manufacturing roughness really the only reason we don't see optical interference in thick dielectrics like windows?

I had always kind of wondered why we didn't see interference in things like windows -- we were taught that the condition is that the thickness of the film/slab/medium just has to be an integral number ...
7
votes
1answer
632 views

Why are black mosquito nets so much less visible than white ones?

I have just been installing a couple of mosquito nets for windows in our apartment. The material is polyester, fibers are approximately 0.2mm thick, and the hexagonal "holes" apprixmately 1.5mm in ...
7
votes
3answers
331 views

If light is linearly polarized, does it have some spatial extent?

If light (a photon) is linearly polarized, say vertically, does it have some vertical spatial extent (perhaps in amplitude)?
7
votes
1answer
4k views

Transparency of materials

Is transparency of material has something to do with inter- or intra-molecular bonding? E.g. both graphite and diamond are carbon, but graphite is opaque and diamond transparent.
7
votes
3answers
229 views

Is that a result of thin-film interference?

Several years ago, I was laying on my bed and had a CD shaped transparent plastic disk (which was covering a 100 CD stack), basically a transparent CD. I don't know why but I took my phone and took a ...
7
votes
2answers
518 views

Why does Pyrex glow orange under UV?

In a Physics lesson today our teacher performed a demonstration to show how quinine in tonic water glows blue when under UV light. He showed us the same demonstration using water in a Pyrex beaker, ...
7
votes
2answers
215 views

Why is condensed milk glowing green under UV?

Teeth, nails and also сгущёнка (condensed milk) are glowing green when exposed to black light. What do they have in common? Is it a specific luminophore substance?
7
votes
3answers
13k views

Why does red light travel faster than blue light?

I know that light of all frequencies travel at the same speed in vacuum. But I wonder why their speed differ in any other medium, why does red light travel faster if it has less energy than blue ...
6
votes
6answers
5k views

Is it possible to witness a circular rainbow?

What conditions would make it possible to see a naturally occurring fully 360° circular rainbow? Would it even be possible?
6
votes
3answers
1k views

Reflection at intersection of two mirrors

Consider two mirrors, which intersect at an angle. Let us talk about geometric optics. If we draw a light ray intersecting the mirrors at their point of intersection, how will it reflect? What will ...
6
votes
6answers
638 views

Why isn't it allowed to use a flash when taking pictures in a certain place?

When I go to, for example, a museum I try to take some pictures. Sometimes the museum staffs forbid me to use a flash. Do you know the reason? I don't think it is related to photo-electric effect, ...
6
votes
4answers
2k views

Colors from a computer vs. colors from visible spectrum of sunlight

Observation: So, I know that all computer screens are able to project many different colors by varying how they display the RGB (Red, Green, Blue) pixels. Question What's the difference between say,...
6
votes
4answers
2k views

The Sun as a gravitational lens

Since the Sun is a gravitational lens with as focal length of 550 AU for visible light, with an immense amplification factor, shouldn't it light up objects hanging out there? We should get solar ...
6
votes
2answers
2k views

Why doesn't my pinhole camera work?

We all know that light travels in straight a line, which can be proved by pinhole imaging as in the picture shown : But when I'm doing this little experiment with an apple, no matter how I change ...
6
votes
4answers
824 views

Why is the sky blue: For a 3-year old [duplicate]

My nephew asked me yesterday why the sky was blue. I tried to explain it to him as best and as dumbly I could, but I failed. I tried to explain the concept of scattering of light using an analogy of ...
6
votes
6answers
1k views

How can molecule of a few angstroms absorb visible light of a few hundred nanometers?

I guess visible light is visible, because it has the right wavelength to be absorbed (or not) and emitted (or not) by many different molecules. Now visible light has a wavelength in the order of a few ...
6
votes
2answers
1k views

What would we see in the sky if it weren't blue

What would we see during the day when we look into the sky (other than clouds), if it weren't for Rayleigh scattering making the sky blue? Would the sky be dark, like at night?
6
votes
2answers
953 views

Homemade Spectrometer

Recently I have had ideas of how to build a spectroscope, but I'm not sure if it will work. As can be seen in the diagram, the experiment is simple: it consists of a laser that generates the light ...
6
votes
5answers
544 views

Blue light filtering

Prologue: my knowledge in these topics is fairly limited, so please feel free to point out the mistakes or the not-so-clear points, and bear with me for the oversimplicity of the language used. I was ...
6
votes
1answer
844 views

Test whether a glass prevents you from getting your Vitamin D portion?

I work in an office with glass, which I believe filters the UV radiation of the sunlight. Is it possible to test if exposure to the light coming through the glass will supply Vitamin D for me as a ...
6
votes
5answers
685 views

What are colors?

If you go to any course about photography, you learn that all colors are made up of the colors red, green and blue (RGB). (If you mix red, green and blue light, you will get white light, or any other ...
6
votes
1answer
487 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 ...
6
votes
4answers
263 views

Is light amplitude spatial?

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 ...
6
votes
5answers
485 views

Trapping a lightray

Given a solid whose interior is a hollow sphere with perfectly reflecting mirrors. A small hole is drilled in the sphere and a photon is sent in at some angle. Will it always eventually exit through ...
6
votes
5answers
594 views

What exactly are light waves?

We know a sound wave is a disturbance that moves through a medium when particles of the medium set neighboring particles in motion. And using the pressure variations we can plot a pressure/time graph ...
6
votes
3answers
414 views

Can visible light be emitted from a non-thermal source?

I was reading about thermal and non-thermal radiation and I was wondering if visible light can be emitted from a non-thermal source?
6
votes
3answers
424 views

Why does light seem to occlude objects in front of it

My question: why does light seem to occlude an object in front of it, especially when viewed from a distance? E.g. imagine a grid-like structure (for example an empty gasometer) viewed from a distance,...
6
votes
5answers
463 views

What is the difference between heat and light?

What i know is that light is an electromagnetic wave. Is heat also an electromagnetic wave of certain wavelength other than light ? Why the light wave cause heat in an object when it falls on the ...
6
votes
5answers
1k views

Can we change a photon's frequency in mid-air?

Can we have a light source emitting photons in the infrared range and after, lets say, 5 meters, these photons become a photon in the x-ray range? The only way I know we can change a photon's ...
6
votes
6answers
9k views

How to Make RF Waves Visible

I understand RF (Radio Frequency) Waves are electromagnetic waves and a mode of communication for wireless technologies, such as cordless phones, radar, ham radio, GPS, and television broadcasts. Most ...
6
votes
2answers
3k 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?
6
votes
2answers
619 views

Blue-shifting as opposed to violet-shifting

A recent XKCD comic implies that the sky is blue as opposed to violet due to human physiology, and that animals more sensitive to shorter wavelengths will perceive the Earth's sky as the shortest ...
6
votes
2answers
411 views

What is changing in latest light bulb technologies?

I'm confused with the latest home lightning bulbs. Understanding filament bulbs was easy. For example take 220V, 100W filament bulb: Power = $V^2/R$ Filament gets heated and emits energy in the form ...
6
votes
2answers
481 views

Single-mode fibers and ray-theory of light

I have read ray-theory cannot be applied to single-mode fibers. Why? I know rays are kind of an approximation to describe the real behavior of light, and electromagnetic theory and photonics are ...