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)

1
vote
1answer
28 views

Diffraction grating (finding number of emission lines)

I came across a question on isaacphysics.org where youre given information about a diffraction grating, the spacing of the gaps and the colour and location (in degrees) of 8 different maxima, of four ...
5
votes
1answer
85 views

Why are UV protective eyeware Orange?

Many industrial processes use uv as a curing agent. When one uses such a process, one must protect one's eyes from the radiation. Most uv protective gear I have seen is tinted orange? Does this ...
0
votes
0answers
18 views

Frequency combs measurment

How is a frequency comb actually used to measure something? For example: I don't know the length of my pen, so I take a ruler and measure it -- it reads 10 cm, so now I know my pen is 10 cm. From my ...
2
votes
0answers
30 views

Is it possible to see an infinite distance in a vacuum, or is this prevented by dispersion? [duplicate]

I just came across the old cliche that describes a star as a "little candle that shines its light so far," and am curious whether, barring obstruction and interference, one might be able to detect a ...
1
vote
1answer
39 views

Newtons corpuscular theory

I am learning about the history and evolution of certain physics theories, one being Newtons corpuscular theory. I am reading that Newton predicted the corpuscles, which make up light would travel ...
3
votes
1answer
89 views

Why purple seems so to similar to red? [duplicate]

Purple lights has the highest frequency among all visible lights, while the red lights is the least frequent one. However, purple seems to be a mix of red and blue to human eyes, why?
3
votes
4answers
149 views

Capture the entire light field of a 3D scene and construct a virtual scene

I've been fascinated with light field cameras for quite a while. They are devices that can capture information about the light field emanating from a scene; that is, the intensity of light in a scene,...
0
votes
1answer
44 views

Speed of light in vacuum in special relativity

In special relativity, the speed of visible light is defined as a constant. But visible light is only a small part of the electromagnetism field. So why?
3
votes
1answer
51 views

Is the photoelectric effect 'Ionising Radiation'?

According to the definition on Wikipedia, ionising radiation is radiation which has sufficient energy to remove an electron from an atom. So a high energy gamma ray is definitely ionising, but visible ...
1
vote
1answer
52 views

Stacked motors thought experiment

first of all, I'm not a mathematician, just curious about something that came up to my mind and maybe you can help me out. Scenario: I have a motor that spins let's say at 20K revolutions per minutes....
15
votes
1answer
949 views

Why is everything not transparent? [duplicate]

There is a related question on this site here: Why glass is transparent? Which explains that glass is transparent because the atoms in glass have very large energy differences between energy levels ...
1
vote
2answers
55 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?) ...
0
votes
3answers
77 views

Can electrons emit light when they are independent? [duplicate]

If an electron is independent, it is an individual electron, i.e. not in the orbit of the atom. Is it able to emit light or does the orbit have to do with the production of light?
0
votes
0answers
35 views

Splitting an image in a lens into two sources?

Is it possible to project an image of light that passes into a lens onto two surfaces without affecting the image?
1
vote
1answer
68 views

What Color Are Black Holes Really? (Yes, a serious question)

So I got into a mini-debate in science class today because I proposed that black holes aren't really black, they only look black because light can't reflect off them. But if you were to take the ...
8
votes
4answers
177 views

Why do the edges of glass blocks create a shadow?

I have always observed that the shadow of glass blocks becomes darker as the glass is moved away from the surface where the shadow falls. And I know this is because refracted light rays from the glass ...
1
vote
0answers
81 views

Why does Light change color through Glass slab?

I shone a green laser light(~532 nm) through a glass slab and what I saw inside was that the light beam was now red. Imagine a regular refraction diagram but color the beam outside green and that on ...
0
votes
2answers
49 views

Physics : Light [closed]

Let us assume that 4 person s are sitting on 4 corner of square ABCD. All have their eye on same level from ground.person looks person diagonally. Now when light goes from A toC and B to D then rays ...
4
votes
2answers
194 views

Does an object travelling at the speed of light cast a shadow? [closed]

Asked by my 8yo today and left me scratching my head.
0
votes
0answers
20 views

Transmittance of yellow light through blue substance

I am performing an experiment in which I flash an LED-light through a substance with different opacities and do voltage measurements over a photoresistor on the other side. When I decrease the ...
1
vote
0answers
37 views

Why do different color materal differ temperature in the same sunlight?

I have a blue, red, and green cup and put a thermometer in each. Of the 3 the blue cup had the coldest temperature inside, then green, then red. I understand there may be differences in the ...
1
vote
1answer
28 views

Diffraction pattern from laser shone on coffe-filter plastered on glass pane

I make an ordinary coffe filter wet and plaster it on a glass pane. I then shine a laser onto the filter (on the side of the pane with the coffe filter). When I do this, I see what I assume is an ...
4
votes
1answer
57 views

How much of Ultraviolet is cut out when Sun moves to the Horizon?

EDIT: Original question was whether or not we need to wear sunglasses when Sun is at the horizon. But it was confusing to many users whether it is on-topic or not. So the details are adjusted. From ...
3
votes
1answer
44 views

Momentum transfer of Light to Object

Can light made of photons in theory topple lets say a car? I know basic photon energy is hv where v is frequency. So according to conservation of linear momentum, if high enough and large amount of ...
2
votes
1answer
27 views

Mueller matrix and Lorentz group

I have just learned about Stokes vectors and Mueller matrices for description of polarized light. In the text I studied there is clear restriction for the Stokes vector $\vec S$ that $S^2_0=S^2_1+S^...
0
votes
1answer
46 views

Particle nature of light [closed]

How particle nature of light can be observed in material world? To common man light does not hit them or make them fall when light beam is projected on them.
-1
votes
1answer
85 views

Characteristics of electromagnetic radiation

Is it possible to change the wavelength of an electromagnetic wave without a change of medium?
51
votes
4answers
4k views

Why does moonlight have a lower color temperature?

Moonlight has a color temperature of 4100K, while sunlight has a higher color temperature of more than 5000K. But objects illuminated by moonlight don't look yellower to the eye. They look bluer. ...
1
vote
0answers
32 views

Light through micro-perforation [closed]

I am trying to have a metal film with micro-perforation lit from one side by LED so that only the perforated pattern appears on the other. Example: Misfit Shine How do I calculate the film thickness,...
1
vote
0answers
46 views

Question related to optics [closed]

My teacher asked me a question, the question is this "Sunlight enters into a room thorugh a triangular aperture, when i place a screen nearer to the aperture it casts a triangular image, but when the ...
0
votes
1answer
21 views

What is the difference between 'Illumination' and 'Illuminance', if any?

What is the difference between 'Illumination' and 'Illuminance', if any? From my knowledge, both of them have the same unit, the lux. So are the two words used to refer to the same parameter or are ...
1
vote
1answer
33 views

Why are some Air Gap Sparks Orange?

While testing the ignition system on my car with a variable gap spark tester I noticed that the spark was orange. I suspect that there may be a problem with the ignition coil such that there is ...
2
votes
0answers
50 views

Lenses that pixeliate incoming light [closed]

Is it possible to make a lens that 'pixelates' the light passing through it? I imagine a pair of glasses, that when put on, turn the world into a grid of discrete pixels, each having, or appearing to ...
1
vote
1answer
59 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 ...
0
votes
1answer
65 views

Why do objects not appear invisible?

I have taken views of many websites and books about how objects have color and they offer only one explanation: it's because they absorb all other colors and reflect color of only one wavelength and ...
2
votes
0answers
44 views

Printing zone plate with laser printer

I tried to print my own zone plates on transparent plastic with laser printer with this generator. I prepared a lot of plates with different settings - focus from 4 to 60 cm, 3 wave lengths, etc. Yet ...
1
vote
2answers
90 views

Why aren't clouds multi-colored?

Clouds are made out of tiny droplets of water. These droplets, to my understanding, act like tiny prisms (which is why there are rainbows after rain). From my line of thinking, if we had a room with ...
0
votes
1answer
27 views

Illuminance on the vertical façade from the ground

I am trying to understand the illuminance on a vertical façade from the light reflected from the ground. And am reading this through Daylighting and Architecture book. On page 41 it makes use of two ...
55
votes
3answers
10k views

Why do beams of light (from torches or other directed sources) not extend to infinity?

When I'm in a dark environment, and I turn on a torch, I can see the beam of light from the torch. To the best of my understanding, the main reason why I can see the beam of light is that the light ...
1
vote
1answer
26 views

What's wrong with finding the maximum refraction angle? [closed]

I am wrong with this derivation of $1 = \mu^2$ for arbitrary $\mu$ obviously, but I can't find what's wrong. $\delta := \theta_{1} - \theta_{2} $ where $\frac{\sin \theta_{1}}{\sin \theta_{2}} = \mu_{...
0
votes
0answers
59 views

Do photons traverse through the vacuum of outer space as a helix? [duplicate]

I’m trying to understand “Electromagnetic waves”. If electromagnetic waves traverse as a helix then do photons traverse as a helix?
0
votes
0answers
12 views

Light scattering and absorption in material

I would like to get your inputs on a way for measuring light characteristics (scattering + absorption) in a specific tissue. My aim is to compare characteristics at different wavelength vis and nir. I ...
1
vote
0answers
33 views

Intersection point of two wires

When I observe two thin wires (up to 1cm, relatively) at a distance, if those two wires are intersecting (but may or may not have physical contact) the absolute point of their intersection is ...
4
votes
2answers
166 views

Why aren't the hottest stars mostly invisible due to radiating mostly in ultra-violet? [duplicate]

The hottest stars have surface temperatures in the range of 40,000K. Wolfram Alpha says that such a star acting as a black body should radiate almost no energy in the visible spectrum. Why then do ...
1
vote
3answers
79 views

If energy of a wave is proportional to frequency, why are higher-powered lightbulbs brighter?

E = hf. Got it. P = dE/dt, right? Not seeing an amplitude anywhere in the formula, so shouldn't the power rating on the lightbulb only be driven by the color? Is it a problem with the way the ...
0
votes
2answers
53 views

how to see photons

I recently saw a couple of videos, in which you could visualize photons traveling through something (a bottle, for example). So my question is: how does it works? How can we see light if it doesn't ...
0
votes
1answer
101 views

Why can I see a beam of light coming in through the window sometimes, but not all the time?

Does it have to do with moisture in the air? Does it have to do with the window itself? Could the light reflect/refract off of the air? If there were no moisture or smoke or dust, just air, would I ...
0
votes
2answers
80 views

Why do electromagnetic waves diffract? [duplicate]

The expansion of electromagnetic waves due to diffraction can be easily explained with Huygens' principle (and in introductory courses this is usually how it is explained). But Huygens' principle is ...
0
votes
1answer
39 views

What will happen if you move a photon move in a straight line with no oscillations? [closed]

As light is a wave, it travels in an oscillating pattern: | _ _ _ _ _ _ _ _ |/_\ _ /_\___/_\ _ /_\___/_\ _ /_\___/_\ _ /_\___ | \_/ \_/ \_/ \_/ \_/ \_/ ...
-3
votes
1answer
60 views

Why is there a cap on the speed at which we can attain? [duplicate]

Also, If you are traveling 1 mph under the speed of light on a train and throw a baseball in front of you at 20mph what would a viewer outside the train see?