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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33
votes
6answers
4k views

Does a “capacitor” for light exist?

If I have a light that is flickering at a frequency low enough to be perceived by the human eye, is there any type of material that exists that will smooth out the appearance of flickering? Similar to ...
0
votes
3answers
46 views

Is a light wave's amplitude stretched, along with the “red shift” stretch - making it brighter?

When light waves are stretched and "red-shifted", is the amplitude of the light wave stretched as well, affecting the intensity/brightness of the light wave?
14
votes
2answers
1k views

The speed of light upon reflection [duplicate]

(NOTE: I am an 8th grader, so I may not be capable of perfectly elaborating my point by scientific measures. Also, English is not my first language) I have read that the speed of light is constant, ...
0
votes
0answers
85 views

Does a “capacitor” for light exist? [duplicate]

If I have a light that is flickering at a frequency low enough to be perceived by the human eye, is there any type of material that exists that will smooth out the appearance of flickering? Similar to ...
2
votes
1answer
49 views

How is the amplitude of light related to number of photons?

If you increase the number of photons leaving a light source you increase the brightness/intensity, so it could be said that intensity is directly proportional to number of photons. However intensity ...
18
votes
3answers
563 views
+100

trouble reconciling doppler shift for energy and momentum of light

[See late addition at bottom for what currently remains unresolved in this question.] I have seen the assertion in a couple of places that if you trap light in a reflective resonator, or any other ...
0
votes
1answer
32 views

Software/apparatus to measure wavelength of visible light

I need a software or an apparatus (avaiable in school conditions) to measure wavelengths of visible light. In my lab I use coloured filters to get different colours of light, but I have to measure ...
11
votes
4answers
2k views

Why do stars flicker?

Why do stars flicker and planets don't? At least this is what I've read online and seen on the night sky. I've heard that it has to do something with the fact that stars emit light and planets reflect ...
-3
votes
0answers
59 views

What is the color of light with white spectrum? [on hold]

I can think of two ways to define the color white: The color of daylight The solar spectrum is approximately that of a black body at ~5800K, with maximum power around the green: The sensation ...
240
votes
22answers
83k views

A mirror flips left and right, but not up and down

Why is it that when you look in the mirror left and right directions appear flipped, but not the up and down?
9
votes
2answers
1k views

Green dot on photos when taking photo facing the sun

When taking a photo towards the sun, I found there is a green dot on the photo. I'm pretty sure this is caused by the sun, the camera has no problem. Question: what is the cause of this green dot? why ...
0
votes
1answer
53 views

What is the process of a photon transforming into an electron and positron? [duplicate]

How did they come into existence from a photon? Is it really understood how the process works? Is there even a process or is it just something fundamental?
-1
votes
0answers
13 views

What is the Lambertian Limit

I am new to this area, and I'd like to find an exact definition of the Lambertian Limit that frequently appears in solar cell related papers.
0
votes
1answer
47 views

Photons inside laser cavity

In a laser, the pumping mechanism excites an electron to a metastable state. This electron remains in the metastable state for a longer time and is de-excited to the ground state by emitting photons (...
0
votes
1answer
326 views

Why the crest of water absorb more light than the trough of water?

I have done my experiment using water ripple to study the behavior of waves. I know that the crest will absorb more light than the trough so that the image created on the white paper sheet appeared to ...
1
vote
1answer
50 views

What happens to the visible light that a substance does not reflect on an atomic level?

Let's say we have a blue, opaque material. If white light was incident on that material, the blue light would be absorbed by electrons and the electrons would transition to a higher energy state, and ...
-2
votes
1answer
33 views

Wave nature of light [closed]

I'm currently working on a project to demonstrate the wave nature of light. Now, my question in specific is: How could the phenomenon of interference be used to MATHEMATICALLY explain the wave nature ...
19
votes
4answers
3k views

Why don't loop currents produce light?

If a charge travels in a circle it must accelerate, thereby producing EM. However, a wire in a circular loop is analogous to many charges moving in a circle. So, why don't circular currents produce ...
-2
votes
0answers
17 views

Finding the index of refraction [closed]

I'm given the angle of incidence which is 60 degrees and the angle of refraction 27 degrees. And two possible indexes of refraction for the second medium which are 1.923 or 2.417. How do I figure out ...
1
vote
1answer
49 views

Are RGB LED's only capable of producing three colors of light? What about all the other colors?

I had a light sensor hooked up to an LED and noticed that it only read a constant lux value when I had any of the RGB values at 255. Anything less made the lux value fluctuate quite rapidly. I get ...
14
votes
5answers
2k views

How many photons are needed to make a light wave?

What is the smallest number of photons needed to make a "light wave"? In other words, how many (coherent?) photons start to exhibit classical behavior? For example, how many photons are needed to get ...
0
votes
0answers
43 views

How Light interacts with Atoms? [closed]

I think I have confused myself about how light interacts with matter, would somebody be able to clear these questions up for me? How does an atom reflect light? Can an electron just essentially '...
2
votes
1answer
27 views

How does infrared light behave through water?

I have a project involving the detection of the presence of water in a cylindrical transparent plastic container (diameter=25cm) And I cannot put any device inside, so I was thinking of using and IR ...
1
vote
4answers
51 views

What is the actual mechanism behind the reflection of various colored light by material of different color?

When light (composed of photons with different frequency and wavelength) falls on a material, some of it gets absorbed and some get reflected depending upon the color of the material on which it ...
9
votes
2answers
1k views

How do color filters placed in front of a light source,change the color of light that passes through?

For instance, placing a blue transparent folder in front of a desk lamp, makes the light that shines through it appear blue. From what I understand some red car lights do not have red light sources, ...
0
votes
1answer
44 views

Density of photons at distance, r, from point light source [closed]

I am trying to derive an expression for calculating photon density $\left(\frac{Photons}{M^3}\right)$ at any given distance from a point monochromatic light source for fun (assuming previous knowledge ...
0
votes
0answers
31 views

How thin can a mirror be? [duplicate]

What affects the reflective properties of a material? From everyday experience, metals are good at reflecting light. How thick should be a mirror to reflect most sun light energy? For the case with ...
3
votes
2answers
111 views

How is light related to photons? [duplicate]

This may seem like a duplicate but I do not understand other explanations. I have read that light is an electromagnetic wave (a fluctuation or disturbance in the electric and magnetic field). How ...
-1
votes
1answer
37 views

Refractive index calculation without using snell's law [closed]

If I have a ray of light travelling from a transparent medium to the air in 70 degrees in the medium and 52 degrees in the air, how can I calculate the refractive index of the transparent medium ...
2
votes
2answers
60 views

Which materials redshift light?

I'm currently researching ways to get the human perceived colors red, green and blue when you only have a mostly blue spectrum available at your source (using electroluminescence). The solution should ...
3
votes
4answers
6k views

Relativistic Doppler effect derivation

This is about a step in a derivation of the expression for the relativistic Doppler effect. Consider a source receding from an observer at a velocity $v$ along the line joining the two. Light is ...
3
votes
2answers
538 views

Finding the illuminance from a triangular light source

Since most light sources in games are point-like, it's pretty difficult to approximate area light sources with point sources. As triangles are a universal form to represent 3D models (thus area light ...
1
vote
1answer
134 views

Calculating the color temperature and intensity of skylight with an algorithm

I think it will be possible to calculate the natural sky light intensity and color balance (CCT) based on time of day/year, GPS location. Has anyone seen a formula/algorithm for this? I would like to ...
0
votes
0answers
32 views

Does the general theory of relativity imply time dilation across the whole universe? [duplicate]

If not, why is my idea below not possible? The general theory of relativity tells us that time is slowed down by gravitational fields. We bounced radar signals off planets further from the sun, and ...
0
votes
2answers
658 views

How to use a magnifying glass or any lens to enhance small light power?

I am currently trying to amplify a tiny amount of light so that a photodiode will recognize it. In order to amplify the light I thought about using a magnifying glass since I got to know that such ...
-4
votes
1answer
28 views

Despersion of visible light [closed]

I was wondering what is the main point for light despersion through a triangular glass prism? Why this dispersion occur?
1
vote
1answer
20 views

Jones formalism for calculating quarter waveplate angle for circular polarized light

I am planning to change the polarization of a vertically linear polarized laser to circular polarized light with the help of a quarter waveplate. I know the final result: I have to rotate the fast ...
0
votes
0answers
16 views

Increasing brightness of light source by reducing apature and reflecting the remainder?

Can the amount of light per area be increased by reflecting all but a small area of the lamp back on the light sources rear reflector or would the reflected light just end up as heat? I attempted a ...
3
votes
3answers
280 views

Why is there less UV light on earth in winter

So I have often read that, at least in e.g. northern Europe, in the colder seasons, there is not enough UV (-B) light arriving from the sun, so many people have not enough vitamin-D from that. At ...
1
vote
0answers
39 views

Is light spectra different for all living bodies? [closed]

As we know that honey bees can see lots of different colours, is it possible that the light spectra is different for them? My main question is that is light spectra different for all living organisms?...
2
votes
1answer
53 views

How does a screen (computer moniter movie theater et cetera) produce the color black?

This might seem a dumb question, but here goes: I can't help but notice that a black screen on my computer looks more like black than the screen when the computer is turned off. Similarly a black ...
1
vote
1answer
75 views

What do we mean by speed of light dependent on direction?

I have a statement in textbook saying: When the speed of light is independent of direction, the secondary waves are spherical. When is it dependent on direction and how will the secondary ...
22
votes
3answers
2k views

Is there a theoretical lower limit to watts needed for lumens?

For example 100 watt incandescent bulb produces 1600 lumens. Led 23 watt can produce 1600 lumens. Is there minimum amount of watts needed ?
-1
votes
1answer
46 views

Change in Speed of Light [duplicate]

Whenever light enters from air to glass its speed decreases but when it cross the glass and again come in air its speed increases. What is the reason behind this property? What is slowing it and what ...
0
votes
1answer
255 views

Dispersion in a rectangular prism

Why are the colours visible only at the fringes of the light refracted through a rectangular prism?
0
votes
1answer
51 views

Can light change the shape of a black hole?

If light orbits a black hole without ever getting closer or further from it, and the black hole pulls on the light from all directions nearly simultaneously, does the black hole extend at its equator? ...
1
vote
1answer
62 views

Why is glass transparent to visible light and opaque to ultraviolet amd infrared light

I was thinking that UL and IL are being absorbed when striking glass which makes no light passing through. need clarification.
2
votes
2answers
77 views

Expanding Universe [closed]

So an expanding universe has the metric $$ds^2 = g_{\mu \nu} dx^\mu dx^\nu = -dt^2 + a(t) ( dr^2+r^2 d\Omega^2)$$ where $d\Omega^2 = d\theta^2 + \sin^2\theta d\varphi^2$ as the usual spherical ...
-2
votes
2answers
60 views

A concept of primary colors [closed]

It's a common conception that there are at least three different colors which produce most of the visible spectrum. I am wondering if there is a unique set of these "primary" colors which could be ...
0
votes
1answer
44 views

Time dilation along a curved path

I was thinking about Einstein's elevator, more specifically, a box, say with one side labeled A and the opposite labeled B. On side A, a laser sends pulses of light to side B at equal time intervals. ...