# Tag Info

18

If it is incandescent, then temperature to some extent, but mostly the light of the wrong color gets filtered out by the colored glass bulb. If it is something like electric discharge lamps, then it is the gas used (eg sodium vapor) or the phosphors coating the inside of the tube converting UV to visible light/color (eg mercury vapor UV emissions). With LED ...

10

For starters, even though you don't say it explicitly, I'm going to assume you're talking about incandescent light bulbs (since you mention filaments in your question). There are many other types of light bulbs, such as compact fluorescent lamp (CFL) or light-emiting diodes (LED). Each of these different types work somewhat differently, and as a result, ...

9

Lasers by definition only emit a single wavelength of light. You use one if you want that wavelength or if you want your photons to be in phase. You don't care about the photon phases, and you want to sample all wavelengths, so a laser is very much the wrong tool. If you just want collimation of the light, mirrors, lenses, or even just well-separated ...

8

Interesting question! Cherenkov radiation would definitely be inefficient for illumination. You only get Cherenkov radiation from charged particles moving faster than the local speed of light in a medium. If you have a transparent medium with index of refraction $n=2$ and you're sending fast electrons through it, you'll only get Cherenkov radiation while ...

7

I am going to answer this on the assumption you are talking about an incandescent lamp. A tungsten filament is heated by the current flowing through it, and starts to behave like a black body radiator. Now a tungsten filament is not a perfect black body: the emissivity is a function of wavelength and has been characterized (see ...

6

Long ago, English speaking sailors measured horizontal distances in units of nautical miles but depths in units of fathoms. The distance in fathoms to some point $z$ fathoms deep and $x$ nautical miles along the surface is $d^2 = 1012.68591^2 x^2 + z^2$. There's nothing physical to that factor of 1012.68591. It's solely a result of using inconsistent units ...

6

To follow the information in Chris White's answer - essentially, you would want a medium that allows you to see the spectra. There are several online resources that could help you in this experiment, in particular, the CD spectrometer, which can be constructed simply and on that website, it shows several examples of how everyday light sources can be ...

5

The quantity $c$ is a very fundamental constant related to space and time. It is largely independent of the existence of matter or light or any other substance. It is probably more ontologically appropriate (if not pedagogically appropriate) to define it as the number that makes Lorentz transformations between reference frames work. The quantity $c$ would ...

5

You speak of fading over seconds. This is not likely to be a result of filament glow in a mains voltage domestic light as they cool very fast. There is unlikely to a sodium vapour lamp in your bathroom either. Most LED lights will turn on and off pretty fast as storage capacitors are expensive to waste. Possibly a thick filament (low voltage) halogen ...

4

"Relativistic" velocities (velocities in excess of 0.1 c) are not needed. Any velocity difference will do. People use the doppler effect right here on Earth. Some sample uses: Catching speeders. How fast is his fastball? (Very important at this time of year.) Where is that tornado going?

4

Your eye has a lens in it. Without a lens, the light is all spread out and overlapping, just like you say. The light from any given pixel goes out in all directions, but a lens can make it re-converge back to a point. Hold up a sheet of white paper. Is there an image on it? No, of course not. It has light on it---light coming from each object in the ...

4

Quite aside from the issue of ionizing radiation, Cerenkov generating particles also lose energy by other processes and that ends up as heat. Moreover, all the kinetic energy of the particles once they drop below the Cerenkov threshold is lost in non-optical channels (i.e. more heat). So no, they could never be anywhere near as efficient as diode ...

3

Very simply, when a plate is quite thick, the fringe patterns will be very close together - because a tiny change in angle will result in an additional wavelength's worth of path difference. Different colors will have a different repeat distance (because of different wavelengths); and light will typically arrive at the eye from more than one direction ...

3

To have depth perception two eyes are needed. Our two eyes are some distance apart which causes the photons from an object to arrive at slightly different angles. The brain then reconstructs the depth field from these differences. Similarly, we can figure out how far nearby stars are by using images made by a telescope at two different times of the year, ...

3

You said that the lamp gave off a yellow glow, so it is possible that it could be a sodium lamp. However, your conception about light intensity and wavelength is a bit off. If the lamp that you are speaking of gives off a monochromatic light source, it is most likely using an electrical current to excite the atoms of a single element. When excited, ...

3

This is a very complicated question and a complete answer would be very deep and very, very long. Much of it stems from the fact that the speed of light is independent of the frame of reference from which it is being observed. In this sense, it is one of few "universal constants" - that is, quantities which do not depend on the observer. Since it has units ...

2

If you reduce the intensity of the light beam so that effectively you know you only have one photon in the apparatus at a time, then what is observed will depend how it is observed. In all cases though, the detected light (photons) will have the same frequency. If you set up a detector so that it records the arrival of photons (note, you cannot have half a ...

2

Cosmology usually adopts something called the "Cosmological Principle", which is that, on large scales. the universe is homogeneous and isotropic. Therefore the universe looks the same wherever you are and looks the same in all directions. Thus light emitted from our part of the universe travels outwards and is received by distant parts of the universe ...

2

Let me go a little further than @mark-h's answer: The behavior of light at an interface is described by the electro-magnetic field solution to the Helmhotlz equation. It gives the reflected and transmitted electric and magnetic components as a function of the refractive indices of the incident and exiting media. From those solutions we can derive the ...

2

This is just an opinion, but the moon on the horizon is simply less visible than the sun is. I suspect that color changes it makes are more subtle and less easily noticed. However full moons are often noticeably orange. Here is a page with a wonderful time lapse view. http://www.pikespeakphoto.com/moon-rising.html

2

In addition to @Floris response: You have missed a lot of wavelengths in your list of wavelengths that would experience interference. Take your example of a $6,000,000 \text{ nanometer}$ pane of glass, and consider that 15,000 waves of $400 \text{ nanometer}$ wavelength light exactly fills this space. So, indeed, this light will experience some sort of ...

2

As you clearly ask for a detection criterion of the doppler shift on "a sample light wave", I have taken the liberty of assuming the following scenario. You detect light from a source, emitting light of a known wavelength (the usual case in astronomy for instance) with an instrument that is capable of measuring wavelength with an accuracy (i.e. with an ...

1

Many light bulbs already do this. See for example this article. I was in the lighting technology business at one point. At that time it was done in some tungsten-halogen incandescents. I don't know current state of things.

1

Everything scattering light has a characteristic spectrum. The spectrum is defined by the way wherein the particular thing interacts with light, and this is set by the (1) chemical makeup and (2) texture (at the wavelength-of-visible light scale). You cannot change the spectrum without changing one of these two things, either by e.g. (1) altering the ...

1

Unfortunately, as interesting an idea as this is, and as creative as you must be for thinking of it, it's not an actual possibility as far as I'm concerned. A one-way mirror works much in the same way that a metallic screen door works. It allows you to see from the inside of your house, outward. However, this is due to the fact that there is far more ...

1

Better late than never? Yes, what you found in the Matlab package is correct. The luminosity function is the exactly the same curve as the green part of the three XYZ Tristimulus Curves used in modeling human perception of color. Note the XYZ color space is not the same as the RGB color space of a display; XYZ represents the totality of what humans can ...

1

But I've never seen that happen. You haven't looked then. The rising or setting Moon is rather reddish, just as is the rising or setting Sun. However, there is a difference between the Moon and the Sun. You can look directly at the Moon, even a full Moon, regardless of where it is in the sky. On the other hand, you can only glance at the Sun when it is ...

1

The spot of light isn't below the line of sight of the laser gun, and the outside observer shouldn't expect that to be the case. The laser gun is attached to the elevator wall, so according to the outside observer, the momentum of photons as they come out of the laser gun must have a non-zero upward component, or else conservation of momentum would be ...

1

Reflection,refraction and transmission of light are macroscopic manifestation of a phenomenon called scattering.In this incoming photons are absorbed and either the quantum energy level of an atom is raised (as in case of resonance absorption) or the outer electron cloud is set into motion(this is responsible for light around us).Almost instantaneously ...

1

Binocular vision has already been discussed, but it left out an important aspect. A single eye is sensitive to distance. The shape of the lens changes to focus on near/far objects. The reason this is needed is that our pupil has finite size and cannot be modeled as a pinhole. The same physics is going on here as in a lens of a camera focusing on an ...

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