# 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.

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### Colors of the Earth from space, an “average” of particular emitters?

When we're say about 100 km above Earth's ground and look down to it and see the Amazonian region as green, is this green color a sort of "average" of greens from trees from that forest or is the "...
238 views

### If you combine multiple laser diodes, will it strengthen the effect?

I found this video (How to Make a Burning Laser Hack ), and it seems to be interesting. I'm curious: If you combine multiple laser diodes, will it strengthen it's effect? For example, if you have ...
28 views

### What changes in the moon light (spectrum, intensity, etc…) after the spring equinox? [closed]

There must be a correlation between the earth moon system and the sun during spring, just after the spring equinox.
28 views

### Minimal size of an optical lens

Is the minimal size of an optical lens (diameter, width and curvature) limited by the wavelength of the incident light?
29 views

### How can I get the sensitivity of some eye cone at a specific wavelength?

The following graph shows the sensitivity for eye cones and rods, but I want to know e.g. what is the red cone sensitivity for a wavelength of 500 nm? How can I find an answer for questions like this?...
39 views

### What is the difference between the light coming from Moon and the Sun? [duplicate]

The moon surface is reflective so, we should have the same light spectrum. And yet there is a difference in the quality of these two lights.
7k views

### What is this shadow being cast upon?

The picture below is from on top of Mt. Shasta at sunrise. The sun was directly behind me when I took the picture and it appears to be casting a shadow on.... the sky itself? Can anyone explain ...
46 views

### Why does a blue book appear black in red monochromatic light?

Why does a blue book appear black in red monochromatic light? I found the question on this website but it doesn't provide an explanation.
62 views

### Why haven't we created a material that is completely invisible to the human eye? [closed]

From what I understand, If something was not reflecting photons in any direction, you could then see through it. If photons transfer into thermal energy could something very cold help? Could the ...
37 views

### Firing Single Photon [closed]

We know (or pretend to know) what will happen if we fire one photon at a time and let it pass through slit/slits. But what if we don't use slit/slits and fire photons one at a time at a screen? What ...
23 views

### Clarification regarding atmospheric opacity

I have taken a look at the related questions Can someone explain to me the concept of atmosphere opacity? and Why can spacecraft observe terrestrial gamma rays, but terrestrial observers not ...
108 views

### Why must $v$ be $< c$ in the Lorentz transformations? Do these equations not apply to light? [duplicate]

I was trying to understand how things look from the perspective of light. Looking at the Lorentz transformations, it seems that the universe would contract along the direction of movement into a plane,...
56 views

### How was microscope-level zoom created by a lens and a water droplet?

It was a rainy night. My glasses were speckled with fresh water droplets. I looked at a distant street light and I was surprised to see cells - a single cell was zoomed in to the level where I could ...
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? ...
18 views

### fiber optic face plate physics-opaque to transparent behavior based on distance of object?

Please look at this video below. its of fiber optic plate or compressed fiber lens Here it seems that the object- which is the book or letters here, is visible only when the plate is touching the ...
28 views

### Why anti-reflective coating of silicon nitride colour varies with thickness?

Why the silicon nitride colour varies with the thickness?
35 views

### What properties would a laser need to have in order to be visible in plain air?

We all know what happens if you use a laser pointer in foggy/dusty conditions: you can clearly see the line from the source to the destination. However, in plain air it is not. My question is, what ...
29 views

### Can refraction be thought of as a special type of reflection?

So, I know the difference between refraction and reflection but I've been wondering today if maybe refraction could be thought of as a special type of reflection with a very obtuse angle. Reflection ...
58 views

### Path of photon from Sun to earth unaltered? [duplicate]

I got into a discussion regarding the light from the Sun that reaches the Earth and whether it maintains the same path from the moment it was emitted to the point it is processed by our eyes. My ...
5k views

### Why does the sun have to be nearly fully covered to notice any darkening in an eclipse?

I was looking at eclipse footage and I noticed that it doesn't get any noticeably darker until the very end when it suddenly all the light is gone. As the moon blocks out the Sun, I would expect that ...
67 views

### How does the levitating water illusion work?

After watching a movie in which levitating water was used as an illusion, I was curious to discover how it works. Unfortunately I cannot find any great explanations of the science behind the effect, ...
45 views

### How come we can get mirror-like effects from dark surfaces?

Question: If I understand correctly, an object's color is determined by the optical frequency which it does not absorb. So an apple appears red because it only reflects red. My question is, if this is ...
33 views

### Cheap DIY Zernike-Phasecontrast: Optical Thickness of a inkjet/laser printed contour for phasering? [closed]

Rough guess: Optical Thickness of a inkjet/laser printed contour? Edit I was wondering if there is any research regarding the refractive index and the height of an inkjet or laser printed contour?  ...
70 views

### Doesn't the doppler effect prove that light is a wave? [closed]

According to me doppler effect can only be applied to waves and not particles, as we apply doppler effect on light it proves it having wave nature and not particle nature.
22 views

### Reason for absorbance

First quoting the example which raised my curiosity"when light passes through polaroid it absorbs certain direction light rays" My question is how this phenomenon of absorbance occurs is this some ...
9 views

### What is the relation between color perception and the lux of white light to which it is exposed?

If we have a particular shade of blue in 100 lux of white light, how will the perceived shade of blue change if the illuminance of white light is increased to, say, 200 lux? or 500 lux? I want to know ...
88 views

### Does every past state of the Earth currently “travel” through the universe?

So I just read this question. The 27 year old user asks if it would be possible to see his own birth if he would be 27 lightyears away from the earth and the answer states ...
970 views

### What is the color of a group of trillions of electrons, protons, and neutrons

Since an electron is smaller than visible light, then what what color would a group of electrons (trillions of electrons) be if there were enough of them to be seen by the eye? What color would a ...
976 views

### Is it possible to have solid light? [closed]

Is it possible to have solid light? If so, what would it be like?
30 views

### What causes the bright glow on the edge of fiber optics and translucent sheets?

http://imgur.com/8PHxy6z On top of the picture, we have a number of translucent sheets. The edge of the sheets seems to glow compared to the rest of the body; why is this? On the bottom of the ...
102 views

### Why doesn't sunlight ALWAYS get split (into monochromatic) when going through the clouds?

It is my understanding that clouds are largely made up of water, which is known to split white light into its frequency components, and that's why we see rainbows sometimes. My question is, with ...
2k views

### What is the farthest planetary body or star system object we have observed using visual light?

What is the farthest object which we can get a direct Detailed visual image of using visible light which appears more than just a dot and falls into one of the following categories: Planet Satellite ...
37 views

### Why does violet (purple) color contain red component? [duplicate]

We see rainbow color on short-wavelength side as violet or purple: And this color is obviously contain R component from RGB. How can this happen, if only blue pines can percept this color, while ...
46 views

### Proving that angle of incidence over angle of reflection is constant in Snell's Law

First let me state what I think I know: Snell's Law states that $\frac{sin(i)}{sin(r)} = \frac{v_1}{v_2}= \frac{\lambda_1}{\lambda_2}= \frac{n_2}{n_1}$ where i is the angle of incidense and r is the ...
32 views

### Self propagating EM waves mechanism of propagation

Electric fields generate magnetic fields and visa/versa,and this is attributed to be how a light ray self propagates. Can anyone further clarify how exactly light rays self propagate? If the mechanism ...
75 views

### The criteria of light

My question is regarding if the "speed of light" 299,792,458 m/s should only apply to certain frequencies of light/colors/amplitude and most the medium in which it travels at 299,792,458 m/s . Shouldn'...
466 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 ...
47 views

### How can you easily measure your visual range? [closed]

There are numerous ways of estimating your hearing range by generating sine waves at a certain amplitude and trying to tell when you are no able to hear a difference between on and off anymore. An ...
40 views

### On parabolic concave mirror in car flashlights

Sorry for the seemingly silly question but what's the advantage of having a concave mirror in car flashlight? I understand how the physics works but I just don't get what the advantage of having this ...
17 views

### Would an HI or HII region have a color?

That is, if we were approaching an HI or HII region in a spaceship, would the cloud have a color visible to the naked eye? Of the HI region, Wikipedia says: These regions do not emit detectable ...
56 views

### Why is 2000 grit good enough for a mirror finish?

The mean particles size on a 2000 grit sandpaper is ~ 1 um, which is not that smooth compared with the wavelength of visible light. But usually when I want a mirror finish, 2000 grit will provide a ...
39 views

### Derivation of Specific Rotation formula?

This is sort of a weird question, so bear with me: I was reading about how chiral molecules rotate plane polarized light and decided to think of a "logical" formula for expressing the amount that ...
35 views

### WHY are reflections stronger at an angle acording to the Fresnel equation?

When looking straight at a glass surface you can mostly see through it, but if you look at it at an angle it becomes more and more like a mirror surface. This is described by the Fresnel equation, or ...
17 views

### Broad Spectrum Contact Lenses - How Soon?

Given the amazing advances in metamaterials, how soon will we have the means to view a broad spectrum of electromagnetic radiation (IR through UV) by having it faithfully compressed into the range of ...
44 views

### Why does our eyes see red when exposed to too much light? [closed]

When I looked into my projector when it was on the blue screen it left a red spot in my vision. I should not have tried it but all the colors left a red spot. Why not a blue or yellow spot was left?
116 views

### How comes unpolarized light do not undergo destructive interference?

As far as I know, unpolarized light is defined as light which as no clear axis of polarization, but electric field vectors in all directions. However, I also know that electric fields can be ...
126 views

### What is the amplitude of a light wave?

Referring to this question How can I measure the amplitude of a light wave? I'm curious about what is a amplitude of a light wave. Especially for light from a thermic source.
74 views

### How can I measure the amplitude of a light wave?

Suppose I have a light wave and I want to measure its amplitude, or check to see if it has an amplitude of a certain value: how would one go about doing this?