Why doesn't a neon sign eventually "run out" of excited atoms and produce dimmer and dimmer light?
472838
Unlike an incandescent bulb which has a filament that can burn out, neon lights have no filament, and have a typical life span of 7 to 10 years, and some have been known to last for 20 years! Neon lights operate on relatively high voltage, but very low amperage (high pressure, but very low volume). Imagine a garden hose with only a trickle of water. Put your thumb over the end, and it comes out with more force, but you use much less water. Just like water pressure, a transformer is needed to increase the electrical pressure to the required current to make the gas inside the tube "glow". Even though neon operates at a higher voltage, the transformer does all the work, thus keeping your electrical load low.
928582
A change in color would indicate some sort of reaction.  xenon is a noble gas and is nonreactive, so no.
105461
Neon gas and Mercury vapor are excited by high voltage to emit light, producing the light spectrum for these elements.\n\nThink neon lights and mercury vapor lights.  Both use a high voltage electrical supply.
518377
Regular (incandescent) bulbs do not emit UV light like fluorescents do. Firstly, the filament temperature is not high enough to permit it to cast UV light.\nSecondly, the glass envelope surrounding the filament is usually made of non-quartz glass which attenuates the UV light.\nThe mercury vapor in fluorescents when excited by electrons, produces + UV light which causes the coating on the inside of the glass envelope to fluoresce thereby producing light.\nBe aware that serious damage can occur to the retina of the eyes if they're so exposed to this light.
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s p d f blocks tell which set of orbitals are the last to fill for those elements.\n\n+ or - depending on whether it will lose or gain an e-\n\ncations are smaller than atoms b/c they lose e-\nanions are larger than atoms b/c they gain e-\n\neach successive ionization energy gets higher becasue the #protons is more and more unbalanced by # e-\n\nhalogens have 7 valence e- and noble gases have 8.  by gaining one e- the halogens now have the e- configuration of a noble gas and are more stable.  gain 1 e- = 1- charge
539515
Moses and Campbelp have it right--the fluorescent light is closer and of larger apparent size (especially if it is a long tube!).  The sun's shadows are not perfectly sharp because it has some size.  This is the cause of the "penumbral" lunar eclipse, when the moon dims but is not fully eclipsed, as it passes through the dim but not dark portion of the Earth's shadow (the penumbra--the darkest part of a shadow is the umbra).
74731
The gas mixture within the latest halogen lamps is designet to interact with the tungsten that is vaporized from the burning filament so that it will not coat the interior of the lamp glass, which wpi;d otherwise dim the bulb, thus extending its lifetime.  It can also be used to affect the spectrum of  the emitted light, with differing gas mixtures altering the emission spectrum.
298815
No a black light is what makes flourescent paint glow.
580964
Gamma decay is probably the one you are after.\nTransitions in the energy levels of the nucleons is the process behind it.\nNuclear Magnetic Resonance is also a nuclear process and would make a better answer as the wavelength of radiation is much safer.
847442
Since there are no metallic ions like sodium or copper to produce intense visible light wavelength emissions, I would suspect that the flame would be colorless or the kind of yellow flame you see at natural gas flaring.  I've not done this experiment (it's pretty hazardous).
651392
None of these are right. An LED wouldn't work without QM (Quantum mechanics).\nA laser is a laser because the dominant process producing light is stimulated emission (StE). LEDs are dominantly spontaneous emission (SpE). As the name suggest SpE is light that just happens, it's spontaneous. StE on the other hand requires photons to seed it, one goes in two come out. Due to this the photons from StE are more "alike" as they are modelled on each other. The key value for a laser is it's threshold. This is the value above which it is a laser, i.e. when the StE process is strong enough to overcome the loss of light in the laser.\n\nedit: sorry couldn't keep quiet, these answers are getting worse. Lasers do NOT have more power than LEDs, for the same size they have LESS power. They do however have higher spectral densities (i.e. more power per unit wavelength). They do NOT have to be collimated. The laser pointers everyone runs around with are only collimated because there is a lens on the front. The laser inside it isn't collimated at all.
681841
Same principle as neon lighting.  With a neon light you have a gas with current passing through it causing it to emit off a light.  In this case it sounds like a concentration of whatever the specific gas happened to be in the air at the lightning strike, and what you saw was the gas emitting it's light.  Anyone happen to know what gas gives off green light in neon lights?
664272
Just goanna tell you why it is like that physically not mathematically but the math part I think you already know.\n\nFor starters there aren't any 2 level lasers there are 3 level lasers and 4 level lasers (4 levels is better then 3) never 2, you will understand why.\nNow first of all you have three processes:\nStimulated emission ;(SE)\nStimulated absorption ;(SA)\nSpontaneous emission;\nThe first two are absolutely symmetric they work with the same constants, they have just one difference, the SE is   proportional to the number of electrons in the exited state and SA proportional to the number of electrons in the fundamental (I do not consider empty places because in practice they aren't really important, don't know if you have saw them if not forget it). Now imagine your gain medium in the fundamental state, you pump it, the medium passes to have more electrons in the exited state, you pump it hard, so now what happens you have the 3 processes. The SA increases the population in the upper level and the SE in the lower level, the SA at first is more successful because there are more atoms in the fundamental state. But you arrive to a point where the population in the 2 levels is equal then both processes have the same intensity, that’s the limit of this system equal population, but you pump even stronger  trying to get an inversion population, what happens? Both process are equal in intensity the population will not vary, now let’s consider the third process. This is a less intense process if you pump well; this will just contribute to the population in the lower level, so you never arrive to have half the atoms in the upper state because even if the SA and SE are equal the spontaneous emission will create one more atom in the lower level.\n\nYou can never have population inversion in a 2 level system. There aren't any lasers with 2 levels, but you can do the calculations for. If you do not understand why population inversion is important here it goes:   you always have lost in your cavity, reflection in the gain medium, output coupler ...Only when you built a laser you see: there are "huge" losses in the laser everywhere. So you have to compensate that with a gain at every passage, well your gain medium only will have a gain > then 1 if you have population inversion, if not your medium will absorb and emit the same quantity having given 0 photons in plus to your system, So you will lose photons at every turn your light will end up really quickly.\n\nNow 3 level systems, in this systems you can pump really hard to the level 3 you can pump electrically by other means, you can pump it optically… but for instance imagine that the only thing getting out of 3 is the spontaneous decay from 3 to 2 only (which is possible, stimulated emission from 3 to 1 might not even be possible) then you can have more atoms in 2 then 1 you have population inversion. 3 level systems are the ruby, first laser ever built, and the Nd:Yag a very powerfull laser, used a lot \n\nIn relation to 4 levels 3 levels systems difference, there you can see the following, when you start to pump in the 4 level systems your base state (in relation to the emission line), is desert you have population inversion immediately, is easier to obtain gain.\n\nTo finalise this part of the answer I can tell you that getting energy out of a 2 level system would be like getting more energy then the one you input it would violate the thermodynamic law the energy conservation principle.\n\nThe second part of the question, I do not now if you where talking in the 2 level or in the 3 level system but I suppose it’s the 3 level system all the way.\nNow the answer to your question is one of most beautiful things that the basic laser physic has, remember you have medium and a cavity, this cavity reproduces it self times and times over. You need the source in 1 to 3 and you create population inversion, now your medium will emit in all directions b
567446
Due to the fusion process taking place inside the sun it emits radiation. The sunlight has solar energy.\n\nIf u would use some other source of light may be artificial then may be the energy generated would be less
121146
Because it takes power from the battery to start the engine.  So the lights get a little less power for that brief instance that the engine gets started.  But once the engine IS started, it produces power on it's own through the alternator, thats why they stop being dim.
275900
Thomas Edison explored this very same issue. He experimented many different components and found that a steel wire in a vacuum lasted longest.\n\nSo yes the light would work, but for a short period of time when the wire, exposed to air, would oxidize then burn up.
138271
This question has two different answers depending on how you read it.  The intensity of the light that reaches you will be reduced as you move away from it, but the intensity of the source stays constant.  Its a matter of perspective, so therefore the preson who asked you this question should clarify it for you.  I'd write both answers and explain each.  Your teacher should except that.