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 (2)

0
votes
1answer
74 views

How many foci does a converging or diverging lens have?

I thought this was a simple question but can't seem to find a direct answer. In ray diagrams with a converging or diverging lens, we always draw F (the focal length) on both sides of the lens. But ...
0
votes
2answers
55 views

When does a monochromatic beam of light on a reflective surface get completely transmitted?

My book says when when a monochromatic beam of light is normally incident on reflective surface it gets completely transmitted. I am bit confused could you explain me?
0
votes
1answer
55 views

An accelerated charge produces an electromagnetic wave. Is light an electromagnetic wave despite not having charged particles? [duplicate]

Light is an electromagnetic radiation contrary to the law of electromagnetism that states that: an accelerated charge produce electromagnetic wave. Please explain.
0
votes
2answers
127 views

Plane polarized light?

I have heard about plane polarized light: light wave which has vibration in one plane. My curiosity forces me to ask a doubt, is there any way to produce polarized light wave which has vibrations in ...
0
votes
1answer
44 views

Beam of electromagnetic wave, with radius of 3cm or less

I need to create a beam of electromagnetic wave, with radius of 3cm or less, for distance about few meters. What is the minimum frequency (maximum wavelength) that it is really possible?
0
votes
5answers
85 views

Is anything coloured “infra-red”?

All our day-to-day objects are things we can see, and thus we can conclude that their colour lies in the visual spectrum. Is there matter that does not have a colour within the visual spectrum? What ...
0
votes
1answer
64 views

Is the glass made up of holes that let the light to go through it?

The following passage has been extracted from the book "The Magic of Science-A.Frederick Collins" (1917): Substances of all kinds have pores or holes in them. A sponge has pores that can be ...
0
votes
1answer
512 views

Why do objects of a given color appear white under light of that color?

Under light from the sun, a red object will scatter the red component of light, and absorb all others. Hence, the human eye perceives it as "red". White objects scatter all wavelengths of light. ...
0
votes
2answers
244 views

Image formation at surface of water

Consider a lake full of water which has an object immersed in it. Now, if an observer was at the surface at a sufficient distance so that the light ray from the object is internally reflected, should ...
0
votes
3answers
445 views

Does light color change when refracting? [duplicate]

When light refracts from a medium to a second one, its frequency stays the same, and its wavelength changes. If this is true, why we see the refracted light ray's colour is the same as the incident ...
0
votes
1answer
87 views

Something about things going in black hole?

Don't hit me if the question is too lame but here it goes 1) We all know that to see something light must get reflected from it's surface and then reach our eye's 2) Any thing which goes in black ...
0
votes
5answers
473 views

Can we create invisible things?

We are able to see this beautiful world because of light. When light gets reflected from the object, the reflected light enters our eye retina and thus we are able see that particular object from ...
0
votes
3answers
69 views

Wall visible after light source removed

Let's say you have a lamp pointed at a wall, in a dark room with no other light source, if you turned off that lamp Would the wall still be visible for any amount of time?
0
votes
3answers
252 views

Is everyone seeing the same color as I see? [duplicate]

As the cone cells are different in numbers in people, how can we say that everyone is seeing the color as same? for example the color you are saying as red may be not the one i see as red..
0
votes
1answer
49 views

Why isn't ray optics applicable for marginal rays?

I have been studying light and going a little bit ahead I studied about ray optics and one thing each book had in notes is ray optics is applicable only for paraxial rays not marginals rays, I was ...
0
votes
3answers
194 views

How do we perceive colors outside our gamut?

Let's take an CIE XYZ color space as an example. There are many colors that are outside our gamut - how do we see such a color?
0
votes
2answers
122 views

Dark light filters letting through less light

I'm looking for an explanation on why darker light filters let through less light than lighter filters (secondary/high school level). Although this seems to the layman like the obvious outcome, our ...
0
votes
2answers
362 views

A light and magnetic mirror paradox?

If light is an electromagnetic wave and lightspeed is constant (we ignore spacetime or gravity for this question) why can't we slow down light with a few dozen wellplaced magnets and electricly ...
0
votes
2answers
175 views

Is an electric lamp a transducer? [closed]

Silly thought. A transducer, by definition, is a device that converts variations in one form of energy to another. An electric lamp converts electricity into visible light - the brightness may vary ...
0
votes
1answer
22 views

Semiconductors light emission

Suppose a pure semiconductor, with a direct gap. If I apply a constant voltage to it the electrons will jump to the conduction band. So when I turn it off will it emite light?, because the electrons ...
0
votes
1answer
68 views

Is it possible to produce coherent light with a thermal source? [closed]

Coherent light means monochromatic light and alle waves have the same phase difference. This is given for laser, where the resonator is a potential box and the outgoing waves have the same phase ...
0
votes
2answers
37 views

What is the maximum of information in a beam of light?

If I look at the space I can see the Andromeda Galaxy as a small dot in the sky. If I look through a telescope, I can see the spiral shape. If the saw right through a huge telescope, I could see a ...
0
votes
1answer
12 views

Recalculating lux from EV

I have to calculate amount of light from IR emmiter. The only equipement, that I can use is Sekonic Light Meter like this one: http://www.ebay.com/bhp/sekonic-l-358 The problem is that i need to have ...
0
votes
3answers
69 views

UV filter, does it exist?

On the video here https://www.youtube.com/watch?v=o9BqrSAHbTc, Thomas Leveritt uses a UV filter which, as far as I understand, lets only the UV through. I couldn't find any photo filter that do that. ...
0
votes
1answer
24 views

How does the flow of photons (qty/s) vary across the spectrum? (In everyday life)

Humans see only a narrow band of light wavelengths. Many animals see much deeper into infrared. Maybe one clue to explain why we don't see IR naturally, has to do with the light intensity as a ...
0
votes
1answer
30 views

Duality in Electromagnetic Spectrum

Is visible light the only portion of the electromagnetic spectrum that exhibits particle/wave duality? If so, how/why do other frequencies (i.e. radio) behave as waves?
0
votes
4answers
45 views

Is there some difference between blue light and light covered by blue paper?

Let´s talk only about photons absorbed by detector. Would it detect something else if the photons came from blue star than if the photons were filtered by blue paper? And what about ultraviolet ...
0
votes
1answer
106 views

Is it possible to project black light? [duplicate]

A thought passed by me and I wondered if projecting black light was possible. We can make lights with many other colors, but I'm not so sure about black. So, is it possible? Has it been done?
0
votes
1answer
766 views

Effect of varying distance of light source from a Light Dependant Resistor

I'm doing the experiment described here and I have a few questions about it. I have a miniature light dependent resistor (LDR) hooked to a multimeter set to $\Omega $ and a $25\,\mathrm W$ Light ...
0
votes
2answers
46 views

Why doesn't the color of an object change when signal of different frequency impinge upon it?

Correct me if I'm wrong but I've always thought that the color that an object has is due to the oscillation of the atoms that makes up the material of that object. When white light is shine upon an ...
0
votes
1answer
76 views

Why do we perceive a colour?

White/yellow light hits a red case, and the red color is reflected into our eyes, since other wavelengths are absorbed. My question is: since both the paint on the case and the white light have ...
0
votes
2answers
63 views

Why Can You Only See Direct Light In Water From a Lighthouse

Whilst observing a lighthouse, I noticed that I could only see the cone of light reflected in the water when the lighthouse light was directly pointed at me. At all other points, I could just about ...
0
votes
2answers
133 views

Faraday Effect does light bend or lose energy?

I was reading upon Faraday effect when it said Faraday effect causes a rotation of the plane of polarization That in mind, does this mean the light can be bent around or does the light loose ...
0
votes
3answers
94 views

Problem on speed of light

As I was reading special relativity, my book says the speed of light is $c$ with respect to any other thing. Does that mean the speed of an individual photon is $c$ even with respect to another ...
0
votes
2answers
82 views

Wavelength of blue filtered light

Does blue filtered white light have a certain wavelength, or is this highly dependent on the filter and source of light?
0
votes
2answers
110 views

How camera flash can send information

Nikon have CLS a system that allow to trigger one flash with other flash. I don't know how exactly it work from user point of view, I think that one flash (in command mode) can send information like ...
0
votes
1answer
187 views

Why isn't steam/cloud blue like liquid and solid water?

Most of us here are aware as I think that pure water has a natural quest to absorb visible red colour wavelength slightly due do which liquid water and sometimes even ice appears to have a blue colour ...
0
votes
2answers
395 views

Is it possible to project an image onto water? [closed]

Is there a way to create an image/projection in the water? Or form the water to project an image, little dot/pixel? Use some type of frequency to modulate the little dot in the fluid?
0
votes
3answers
287 views

Refraction through prism

We know that the light gets refracted when it enter a medium low/high refractive index. But why light is not refracted when it comes out from the vertex of a prism.
0
votes
1answer
128 views

What is the intrinsic colour of the star? [closed]

Hey I have this question and I am wrestling with it all day and I am completely lost. The V magnitude of a star is 15.1, B-V =1.6, and absolute magnitude Mv= 1.3 The extinction in the direction of ...
0
votes
3answers
1k views

Can a glass window protect from heat radiation?

I have been reading in this and found a statement saying : " Glass will not transmit heat radiation.". So now I am confused. If glass won't transmit heat radiation, then why do we feel hot when we sit ...
0
votes
1answer
162 views

Concentration of photons: How many can you slow down in a given unit of space?

Being able to slow down light to the speed of a bicicle as shown in this vid: http://www.youtube.com/watch?v=EK6HxdUQm5s Led to a question: Given a unit of space e.g. 1cm^3, and then you slowed down ...
0
votes
2answers
125 views

Length contraction as $v>c$

What would theoretically happen to an observed object's length (let it be a 5 meter line) moving at some speed greater than that of light in a straight path?
0
votes
1answer
151 views

Why does a street light cast a wavey shimmer across the water (at night)

See image You will have to zoom in. Why is the reflection a wavey one? Could someone explain how this is occurring, to the layman, (with the style of feynman if possible -heh) :)
0
votes
2answers
361 views

What type of electromagnetic radiation strikes the Earth's surface the most?

If you can could you lists the types of light from the greatest amount to the least amount (Ex: Visible, Infrared, Violet).
0
votes
2answers
8k views

Does more reflective aluminum foil make a room cooler compared to less reflective foil?

Aluminum foil is said to be not absorbing light at all. It reflects light. So, does it mean that a more shiny aluminum foil will reflect more light and thus make the room more cooler as compared to ...
0
votes
2answers
3k views

Light bulbs, Wattage meaning? [closed]

Light bulbs, Wattage meaning? Two incandescent bulbs (120 V, 25 Watt) and (120 V, 500 Watt) connected to the same batteries. Which one shines brighter? And why?
0
votes
1answer
42 views

Can the choice of reflection angle for light can be derived from a minimality condition?

When the light hits on a surface, it reflects with the "same" angle as the one that hits the surface. I was wondering if this choice of angle can be explained by a minimality condition?
0
votes
1answer
243 views

Which fraction of light is refracted from a source of light under a lake?

I was trying to solve this problem: "A punctiform source of light is standing inside a lake, at a height h of the surface. f is the fraction of the total of energy emitted that escapes directly from ...
0
votes
2answers
847 views

The color purple in a rainbow

In a rainbow the colors order is red then orange (made from red and yellow, thus making sense that it appears in between them) the yellow followed by green after which comes blue (again green formed ...