# Tagged Questions

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.

0answers
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### Is it correct that the polarized scatter of a polarized light source is max. orthogonal to the light source?

First of all, is the statement above correct? And if so, is there a constant gradient, with no polarized scatter parallel to the polarized source up to fully polarized at 90 degrees?
1answer
46 views

### What happens when two polarized lights of the same wavelength interfere at 90 degrees with each other?

am I right in assuming that if I cross two polarized lights of the same wavelength the result would be destructive interference? I don't mean 90 degrees as in 'orthogonal polarization', but the two ...
6answers
2k views

### Light's inverse square law: Does it require a minimum distance from the source?

Does the inverse square law begin to take effect the moment light leaves its source? For example, does light's intensity decrease, i.e. does the area in which the photons might land increase, at a few ...
0answers
30 views

### Is it possible to approximately know the wattage/luminosity of a lamp knowing distance and using a DSLR?

I'd like to know if it is possible to approximately know the wattage/luminosity of a lamp knowing distance and using a DSLR (digital single lens reflex camera) mounted on tripod. Maybe, when shooting ...
0answers
23 views

### Why does some peoples' hair look blue when I look out the train window while wearing sunglasses?

Specifically, when I look through the window, black hair looks blue when people pass the window outside, and black shiny benches look like somebody painted them blue. Pretty sure my sunglasses are ...
0answers
14 views

### How does the area of illumination affect the numerical aperture / optical resolution of an optical system?

I have been reading an optics paper in which they designed a microscope with the following setup. A light source passes through a small pinhole, illuminates a sample, which then forms a diffraction ...
1answer
38 views

### What kind of other light sources can disturb the detection of LASER [closed]

My project objective is to detect different lasers , for example Laser Range Finder: pulse width 10ns and repetition rate is ...
0answers
11 views

### When light reflects from a medium of lower index of reflection to a medium of higher index of refraction, why does the light undergo a phase shift? [duplicate]

I learned in my physics class that there is a phase shift when light reflects off a low $n$ from a higher $n$, but never got the explanation.
3answers
9k views

### How is 6W equivalent to 40W, as claimed by adverts for LED light bulbs?

Every advert I come across for LED bulbs advertise them as the equivalent of a higher W incandescent bulbs. This makes no sense to me, if the room requires 40W to lighten it up then it'll always ...
1answer
30 views

### Michleson Interferometer fringe shift

I have a problem with interferometer fringe shift. I am learning it from my physics book. In the book, it is written, "As the L1 (Displacement of moveable mirror) is changed, the pattern of ...
3answers
657 views

### What gives things color? [duplicate]

I know that color comes from things not absorbing a certain wavelength of light, but what property gives something color? Like what property of copper atoms makes copper as a whole brown, or cobalt ...
1answer
59 views

### Why do some elements burn different colors? [duplicate]

I have a torch lighter and it makes a green color when the flame passes over the metal in the center. What on the molecular level would a flame change color although there is no difference in ...
0answers
20 views

### Why emulsions do not show Tyndall Effect?

The particles in an emulsion are large enough than that of solution, but why emulsion does not show Tyndall Effect?
3answers
103 views

### Is this true about low-light/one photon at-a-time double-slit interference?

I've consistently noticed in pictures of double-slit interference when very low-light or one photon at-a-time is used, that there's lots of "stray" photons detected in the areas of destructive ...
3answers
4k views

### Can something without mass exert a force?

I am something of a dilettante in physics, so please forgive me if the answer to this question is painfully obvious. The question is simple, can something that theoretically has no mass exert a force. ...
1answer
81 views

### Backing out of interactions: Does physics account for such a thing?

Does physics account for interactions between light and matter ever being "not completed" or backed out of? Here's what led me to the question. In learning about interference in light, I ended up ...
1answer
42 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 ...
1answer
30 views

### Why is it easier to make inks which show up on white paper than on black? [closed]

Not sure if this is a Physics question, but... Why is it easier for inks to show up on white paper than on black? You can get "special" inks which print solidly on top of black surfaces, but your ...
1answer
64 views

### How does Compton scattering demonstrate particle over wave behavior?

Why is Compton scattering thought to demonstrate light's behavior as a particle over that as a wave. I'm interested in the thoughts at the time of Compton, but also how it contradicts current theory ...
0answers
23 views

### Fresnel Diffraction

In fresenls treatment of a plane wavefront when the aperture is infinty then intensity on the screen must be equal to the intensity of incident wavefront. Intensity comes out to be 1/4 times the ...
1answer
28 views

### Finding Intensity of light incident on a photodiode

Given a halogen lamp(9500lumen,500W) at a distance d from a photodiode. How can I find the intensity of light incident on the photodiode?
3answers
110 views

### Create a laser from sun light

I have read on wikipedia the basic theory behind laser. A photon passes through an excited electron which then produces the exact same photon. Light is bounced off mirrors to create more photons. Is ...
0answers
7 views

### Height of a point in a plane given a measure of luminance

Context Assume a left-hand rule coordinate system and X points right, Y points up, Z points out. I have a camera facing perpendicular to the X-Z plane in the negative Y direction. I have 4 ...
0answers
20 views

### Mirror shake emulation for the light

Is there any way to simulate mirror shaking? Final goal is to make send light beam to the mirror and get reflected beam the same, as it happens if mirror is vibrating. Mechanical vibration is limited ...
0answers
23 views

### Light bulbs Flashing on when disconnected

For the 2nd time I've had a lightbulb flash on in my hand after removing from the power socket. The first time the overhead light in my hallway was out for a couple of days before I got around to ...
1answer
54 views

### Is fire more harmful than a phone?

I have read somewhere that the higher the frequency of electromagnetic radiation, the higher the damage it causes to your body, and visible light has a very high frequency in comparison to microwave ...
1answer
49 views

### What is “Condensed Light”?

It is mentioned in this article It seems to be a Bose-Einstein condensate of some kind, but it is not exactly clear how one can create a BEC with just photons Light consists of tiny indivisible ...
2answers
57 views

### Is the rate of light emissions actually the frequency of the light?

I am confusing with the concept of frequency in the context of Doppler effect studying SR. The Schutz says, if the source emits pulses more frequently, then the observer would see the lights not only ...
1answer
34 views

### Blue light is reflected, red is not. What happens to other visible/non-visible light?

The problem says: The certain film on the glass reflects blue light of wavelength 480nm, but does not reflect any red light of wavelength 640nm. 1) If we say that it reflects blue light but no red ...
0answers
44 views

### Can 2 photons make up the same colour as another photon?

So, my question deals with the excited electron shown above. (1st diagram) This electron can return to its ground state by either of two ways. One of the ways involves the emission of 2 photons. (2nd ...
1answer
57 views

### Glowing light around my shadow during sunrise

This morning I was jogging when the sun came rose. I was in the middle of wheat-fields and noticed that there was a glow around the upper part of body's shadow on the fields. At first I thought that ...
1answer
47 views

### Explain Sun Glare

Above is a picture that I took just before the sun set. Notice the prominent red blob to the left of the sun. Can anyone explain the phenomenon that creates superimposed shapes and blobs in images of ...
1answer
53 views

### Basic question about light

My understanding is: when light hits an object, it can do one of three things: transmit through the object, be absorbed into the object, or reflect from the object. However, I have also learned that ...
2answers
264 views

### Is light getting another color when travelling through a prism?

When white light travels through a prism the speed of this light is slowed down. Now there is a relation between speed of light, frequency and wavelength. So when a red light of 700nm enters a prism ...
0answers
18 views

### Is there a limit to the frequency of light? [duplicate]

I am assuming that light frequency would eventually be limited by Planck distance and/or Heisenberg limitations. Could this frequency ever be approached in practical terms?
2answers
274 views

### Why is infrared radiation associated with heat?

I am little confused with infrared radiation. I understand that when an object is hotter, it radiates electromagnetic waves of a bigger frequency and this waves are also more energetic, that is why ...
1answer
44 views

### Is it scientifically possible to stop a screens polarization by adding a layer? [closed]

Back story: At work we deal with confidential data, however our desk layout does not allow for screen privacy. We do not a privacy screens and are not allowed to take apart our screens. In searching ...
1answer
50 views

### why my eyesight glasses the color of the things I see?

I have started to need eyesight glasses (I am short-sighted) a while ago and I am puzzled by the fact that when I wear my glasses the color of the things around me are less bright than when I don't ...
3answers
146 views

### Do gravitational waves affect light?

Gravity "bends" light, predicted with theory of relativity and subsequently observed: how does gravity and gravitational waves achieve this effect, and shouldn't this effect be present wherever there'...
0answers
60 views

### Cherenkov Luminescence Imaging, Cherenkov radiation,

Is it possible to see glowing from Thin Layer chromatography (TLC silica gel on Aluminium) when we image it by IVIS spectrum (no radioactive source)?
1answer
40 views

### Sphere, silver reflector, refraction questions

A sphere with its back silvered can act as a retroreflector. When a fine beam of light is directed to the sphere as shown, it is refracted at the front surface, and focused on the rear interior ...
1answer
37 views

### Tricky Optics Questions, shifting lenses [closed]

A candle is placed at a fixed distance in front of a wall. A lens is inserted and moved slowly between them. At two particular positions, sharp images are formed on the wall. The heights of the images ...
1answer
86 views

### Given is an object which is cyan when illuminated with white light. What is the perceived colour of the object when illuminated with yellow light?

I know the perceived colour of an object depends on which wavelengths of the incoming light are reflected and not absorbed, which lead me to believe that it is impossible to be red or yellow... I ...
0answers
33 views

### Doppler shift of light from stars and galaxies [duplicate]

I was reading about how we can ascertain whether a cosmic object is receding from or approaching us by studying the doppler shift of its spectrum- I mean the redshift and blue-shift. But we have no ...
0answers
14 views

### Color Temperature Variation of Sunlight

I want to know what is the Variation of the color temperature in Kelvin of Sunlight as viewed from the earth from Sunrise to Brightday to Noon to Sunset. Will there be any change in the color ...
1answer
60 views

### Can two different RGB color triplets give the same color?

It is easy to understand that RGB color models cannot represent all colors. First the coding on a finite number of bits (16, 24...) cannot reproduce the infinite number of tones. Second, the RGB ...
0answers
20 views

### can you concentrate diffuse light?

how do you turn diffuse light into direct light?
1answer
85 views

### Why is glass green?

When I look at a glass block at an angle the edges appear green, but when I look at the edge sideways, so that is directly in front of my eyes it appears transparent. Why?
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 ...
1answer
82 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 ...