Active questions tagged visible-light - Physics Stack Exchange

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Why does the sky after sunset mimic the blackbody spectrum?

There are several answers on this site and elsewhere about why the sky is blue and why sunsets are reddish. But I could not find anything that discusses the relationship between the blackbody spectrum and the spectrum of colors seen above the horizon after sunset. In particular, the "physical spectrum" (meaning the set of colors seen in the sky...

Why do two blurry shadows, when brought close to each other, appear to "bulge" and merge?

I have recently noticed that when two objects with blurry shadows cast by the same light source are brought close to each other, their shadows appear to merge in a way where one shadow appears to "bulge" and meet the other even though the two objects are not in contact. I noticed this in my bathroom while I was brushing my teeth. Here is a gif of the...

Why do people say we need general relativity in order to explain why light is affected by gravity?

I've heard said by many physicists things along the lines of "Since light has no mass, we need general relativity to explain why light is affected by gravity." But why is this necessary? We know that light has energy $E=h\nu=\frac{hc}{\lambda}$, and we know that gravity is really based on total energy and not just rest mass, so therefore light has...

Why do colours change in water

I was doing my swimming rounds, when it turned dark, so the pool management turned on the lights. The lights were actually yellow in colour, but they appeared green if I moved far away from them underwater(6 to 7m). They looked yellow above water. Someone please explain this.

A unique phenomenon related to shadows [duplicate]

yesterday I was creating shadows with my hands and observed this - when i bring 2 fingers very close to each other and see its shadow on screen the fingers are distant in real but their shadow kind of bends . this is how(please see picture below).. can someone please explain it. its just out of curiosity.

Is our universe (not space-time) curved if very distant objects images differ from expected?

Images of very distant objects are larger than expected and more curiously for even more distant objects the images become smaller.Can this fact suggest that our space(not space-time) is curved which can be compared with a two dimensional sphere surface but with an extra dimension?Could these even more distant objects make focus of their light at the...

Why does light not produce sound?

We have heard about the definition of a wave - disturbance in the matter or something. But can we think that light is a wave and so does it have vibrations (oscillations). Does it produce sound then? I am not talking about our audible range and consider it in our atmosphere only(material medium).

LED Lens to narrow output from multiple sources

I am trying to place a 30 degree LED lens over 4 small 5050 led chips, however the range of lenses available don't appear to cater to exactly what I need. Are there such lenses made that allow a wide surface area of light to be narrowed down to a smaller surface area? Like a cone shape I guess.. I am basically trying to input light from 4 LED chips...

what's the track it will be for light?

Let's suppose one shaking light starts from Proxima Centauri and travels toward the earth. We know light will travel from more 4 years to reach the earth. It will be interesting if we 'look' at the travelling light in space (suppose we can), the light should be shaking in space, shouldn't it? we will see a shaking light, or a bending light. However,...

Qualitative analysis of dielectric interaction between dielectrics and conductors - how/why do dielectrics have color?

For some context, I'm trying to understand some of the physics behind "Physically Based Rendering" (PBR) in 3D rendering engines, see for example THE PBR GUIDE BY ALLEGORITHMIC - PART 1 THE PBR GUIDE BY ALLEGORITHMIC - PART 2 I'm doing this pretty much to satisfy my own curiosity. I do come from a physics background (masters degree in computational...

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