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Incandescence?
saltiness
Registered User regular
Registered User regular
I had an argument with my teacher yesterday about incandescent light sources. He claimed that the sun was an incandescent light source while a photography strobe (or flash) is not. I asked him why the sun is incandescent and he said it's because it glows by heating metal (iron). I called bullshit and explained that the sun radiates photons because of nuclear fusion. Light is emitted by Hydrogen and Helium atoms. He said yeah ok but a strobe emits a "burst" (his word) of light and it is not continuous. It also is heating up Argon gas to emit light so it's not incandescent so he says. I told him that a) I believe photography strobes use mostly Xenon gas and b) this does not explain why it is not incandescent and the sun is. My instinct tells me that neither the sun nor a photography strobe is incandescent.
Eventually I dropped the argument because I didn't want to waste the other students time.
TLDR; Is the sun or a photography strobe incandescent?
Eventually I dropped the argument because I didn't want to waste the other students time.
TLDR; Is the sun or a photography strobe incandescent?
XBL: heavenkils
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First, they're totally different spectra.
Secondly, they're two different sources of light. Incandescent light is produced by heating up a material to a high temperature. Sunlight is one range of electromagnetic radiation produced by nuclear fission.
I don't know about a photography strobe, but according to Wikipedia they work by sending an electrical current through ionized xenon gas, which would mean they're not incandescent, either.
the "no true scotch man" fallacy.
the sun is a mass of incandescent gas,
a gigantic nuclear furnace,
where hydrogen turns to helium
at a temperature of millions of degrees
in this case, incandescence is the release of thermal radiation due to temperature
Light bulbs and stars would be incandescent, fluorescent bulbs and LEDs would be luminescent.
partial credit, but close enough
fluorescent bulbs fluoresce. LEDs work via electroluminescence. both are forms of luminescence, which is any light not generated by high temperatures alone. other forms are bioluminescence (fireflies), cathodoluminescence (crt televisions), and chemiluminescence (using luminol to test for blood ala CSI)
Also, Feral, I'm pretty sure spectra has nothing to do with incandescence or luminscence. It only tells us light temperature and what elements are involved in the emission of photons, not how they are involved. And sunlight is a result of fusion not fission. This still leaves the question of exactly how the sun emits light.
your issue lies mostly in the vocabulary. the hydrogen and helium gas in the sun *is* incandescent, because of the heat. similarly, sticking a poker into a fire until it is red hot causes it to become incandescent (it glows). the filament in an incandescent bulb glows because it is heating up from absorbing the electricity. anything heated until it is "glowing" is incandescent.
you were right in calling bullshit on the professor, because it most definitely isn't the glowing iron that lights the sun. however, the fact that it is glowing from the heat (caused by nuclear fusion) makes it incandescent.
check out http://www.eoearth.org/article/Solar_radiation for more info
also, in the strobe example you brought up earlier, the light isn't from heating the xenon gas, it comes from sending a charge through the gas which excites it, releasing photons as it drops down from the excited state. this is similar to fluorescent lights, which are filled with mercury gas. fluorescent lights differ in that the tubes are coated with a chemical (phosphor) that absorbs the photons released from the mercury, and in doing so release different photons of their own which have longer wavelengths
Are you sure? It was my understanding that incandescent light typically has a specific range of frequencies. If I'm wrong, let me know.
Yeah, I should learn to proofread.
the "no true scotch man" fallacy.
Well, with Hydrogen/Helium the range of frequencies pretty much covers the visible spectrum. So yes, in a sense it is a specific range, but for each element.
Uhh, those are just two parts of the same shape curve
http://en.wikipedia.org/wiki/Black_body
The Sun is, except for lots of absorption lines, a black body. The emission of photons from fusion heats up the hydrogen and other gases in the sun. Those hot gases then radiate a black body spectrum. This is how we know the temperature of the sun, without being able to go and stick a thermometer into it.
Any object glowing due to its heat will produce a blackbody spectrum. Hot metal, fire, incandescent light bulbs, and plasma will all have a blackbody spectrum. So do people, in fact! But our emission peak is not in the visible (lucky for us).
So, if your definition of incandescence is that it looks like a black body, then, yes, both the sun and a light bulb are incandescent. But this has nothing to do with the composition of the sun (which is, in fact, only .16% iron) and would work the same if the sun was made entirely of hot fudge.
edit:
To clarify: what he said about having to be continuous is crap. You can have a blackbody for any length of time you want. I believe a camera flash is not a blackbody, as rannelvis said.
Just because the shape of the curves are sort of similar doesn't mean it's the same spectral output. The graphs have handy X-axis markings so you can see that yes, there is more red in the incandescent bulb's output relative to its yellow output than in the sunlight.
The difference *also* doesn't mean that the sun isn't incandescent, it only means that the spectral output of the two light sources is different.
http://www.thelostworlds.net/
They aren't "sort of similar" shapes--they're identical shapes. Any blackbody curve has the form T = 2hf^3/c^2 e^(hf/(kT)). Their peaks will be in different places depending on T, but they're still the same curve. Read the article I mentioned.