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Author: Subject: What is stronger? Sunlight or artificial light?
RawWork
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[*] posted on 8-4-2018 at 05:55
What is stronger? Sunlight or artificial light?


I won't tell you why am I asking this, because that deserves another topic/thread.

I am asking this. What is stronger per same area? Light from sun in best case (summer) or artificial light in best case (from burning charcoal or lamp or torch or arc).

One additional comparison question is this. What is stronger? Sunlight or thunder light?

Of course I am not asking about theory, like what has more energy or what is bigger or what will release more light in space or somewhere else. But what will release more light on us, on me, on some object I am working with.

I know that sun releases about 1 kWh/m2.

I am thinking practically for heating purposes. I think it's anything artificial because it's solid. That's why we have to use face shields and other equipment, correct?
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Sulaiman
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[*] posted on 8-4-2018 at 06:21


There is no answer to your question because it is vague,
what artificial light source, at what distance, over what area ?
e.g. Stadium lights at close range would kill most plants, a laser would burn through cellular life.

P.S. The sun delivers approximately 1.5 kW/m2 above the atmosphere and 1 kW/m2 at ground level.

NOT 1 kWh/m2 which is a measure of ENERGY per unit area.
ENERGY and POWER are NOT the same thing.




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DavidJR
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[*] posted on 8-4-2018 at 06:30


Sunlight, by far, is 'stronger' than the most frequently encountered artificial light sources. The human eye has an extremely nonlinear response to light (which is actually a good thing as it means we have a huge dynamic range) so it can be difficult to appreciate the difference in irradiance.

Try playing with a fully manual film camera (w/ light meter) and you'll see that in general you need a lot more exposure for bright indoor artificially lit scenes than for a sunlit scene on a sunny/slightly overcast day.
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RawWork
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[*] posted on 8-4-2018 at 06:30


Well, let's say I want to build solar furnace to get 4000 degrees celsius. If I use artificial strong light, i may be able to build it using much smaller lenses than the one is built on our planet, which is too big? If I use same lenses, the one which focuses light from fire will give stronger heat at opossite end. Excluding possibility of direct heat transfer from furnace, that is if lenses are far enough from normal fire, so that only light plays role here.

I am saying this because I don't care about getting free energy, at least not in this case. I just want extremely high temperature to melt, vaporize, react, reduce etc. Best of all light is cleanest, no fans, interactions, impurities, sounds, gases... I can build normal furnace and focus red hot charcoal light?

Yeah I wanted to say kW only. Obviously if I said kW you will imagine it as kW for one hour, as it's easy to convert. Forgot it. Sorry when I edited this line of text I had to reedit it 2 times, because I wrote kWh twice accidentally instead of kW. Probably because I got used to calculating electric energy price.

"The rays are focused onto an area the size of a cooking pot and can reach 4,000 °C (7,230 °F)"

https://en.wikipedia.org/wiki/Solar_furnace

Yes I noticed that. But that is probably because incadescent light source is only small percent of light and rest is heat. If sun is stronger, then why can I watch it with eyes and can't watch red hot charcoal or steel? Why people have to wear face shields when working with torches? How can lasers damage or kill somebody? I have feeling that it's opposite.

[Edited on 8-4-2018 by RawWork]
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NEMO-Chemistry
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[*] posted on 8-4-2018 at 06:42


It takes tiny parabolic mirrors that are positioned constantly by fractions of a mm. There was (maybe still is), a small pilot plant in a desert somewhere that melted salt as the heat sink. A frenzel lens will get very high temps as well, but go careful these things are not toys and serious burns are a real possible.
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Sulaiman
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[*] posted on 8-4-2018 at 07:44


Have you considered an electric arc for high temperatures ?

P.S. Heat radiation varies as (area)x(T4) https://en.wikipedia.org/wiki/Thermal_radiation
so enormous power is often required to heat even a small surface area,
consider for example the tungsten filament area in a filament lamp.

[Edited on 8-4-2018 by Sulaiman]




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RawWork
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[*] posted on 8-4-2018 at 08:31


No, man. Electric arc furnace is no different, actually is worse, than filament or any other. Worst of all dirty, dynamic, wasting...
But I am not here to discuss furnaces, but simply possibility of making stronger temperature using artificial light instead of natural light.

This could be asked in different way, which would i think receive same answer. Can solar cell give more energy if placed near fire or some light instead of in sunlight?
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aga
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[*] posted on 8-4-2018 at 08:42


Some torches are quite bright these days :
https://www.youtube.com/watch?v=pMSyGOoesfM




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[*] posted on 8-4-2018 at 09:18


There are xenon arc lamps that have similar output to that of the sun at short distances but they cost in the thousands of dollars, require a special power supply and cooling system, are pressurized to several atmospheres so you have to wear blast gear when handling them, and only last around a thousand hours.

[Edited on 8-4-2018 by Plunkett]
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[*] posted on 8-4-2018 at 09:22


Quote: Originally posted by aga  
Some torches are quite bright these days :
https://www.youtube.com/watch?v=pMSyGOoesfM


Is the laser using air or oxygen in conjuction with the photons. Quite a light show.
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[*] posted on 8-4-2018 at 09:22


Quote: Originally posted by RawWork  

"The rays are focused onto an area the size of a cooking pot and can reach 4,000 °C (7,230 °F)"

https://en.wikipedia.org/wiki/Solar_furnace

Yes I noticed that. But that is probably because incadescent light source is only small percent of light and rest is heat. If sun is stronger, then why can I watch it with eyes and can't watch red hot charcoal or steel? Why people have to wear face shields when working with torches? How can lasers damage or kill somebody? I have feeling that it's opposite.

[Edited on 8-4-2018 by RawWork]


I think you would benefit from doing a lot more background reading before jumping to your conclusions. People have to wear face shields when working with torches because of the ultraviolet light that is produced. Lasers are powerful due to the coherent light that is concentrated on a small point. And you shouldn't look directly at the sun either, or you may suffer eye damage.
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RawWork
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[*] posted on 8-4-2018 at 12:02


Why am I having feeling that all you all are trying to say is that sun is stronger?
Isn't the sun the weakest?
Can't infrared light and heat also damage eyes? Don't we have to wear face shields because of that too, and not only because of UV?
If sun is strongest, then why i don't feel any damage (heat or uv)?
And don't worry about looking directly in sun, I looked into it directly for hours after reading it's beneficial for health in form of "sun gazing" and "sun tanning". Of course authors recommending that said it's best to do in morning and evening, that is when sun is weakest, no rapid change to be expected, no extreme exposures.
Isn't the laser stronger than sun? If sun were stronger it would cut things, correct? Laser are strongest? I can make 4000 C using lasers?
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[*] posted on 8-4-2018 at 12:43


How powerful is the laser? If you’re talking about a 1mW pointer or even a 100mW burning laser then of course they’re going to do some damage when focused (especially to the eyes), just as the Sun will when focused. When you stand outside, the rays are collimated but there is no natural mechanism for focusing them onto your skin so it doesn’t immediately burn like a strong laser. Grab a magnifying glass though and it’s a different matter, which does about the same damage as the focusing plane of a 100mW+ laser (stinging the skin, melting black plastic, scorching leaves). Make that lens larger, like a 1m Fresnel lens, then you have a large enough power area focused into a small enough point that you can literally melt metal and stone with it. It all depends on the power you are dealing with over a certain area - lasers are low power over an extremely small area, whereas sunlight is a higher power over a larger area, but comparing the area in W/m^2, the laser wins out unless the power from the sun’s rays is focused using a lens.



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[*] posted on 8-4-2018 at 12:51


Quote: Originally posted by RawWork  
... i don't feel any damage (heat or uv)? ...

You feel no heat from the Sun ?

What Planet are you on ?

sciencemadness.org is (currently) based on Earth, a small planet out on the edge of an insignificant galaxy.

Edit:

A quick chat with Polverone confirms that he had a chat with Elon Musk and we should be based on the Moon by 2020, also a Mars data centre by 2023, IF Musk's car crashes there as intended (the boot is full of servers).

[Edited on 8-4-2018 by aga]




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RawWork
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[*] posted on 8-4-2018 at 13:18


I feel heat, but not enough to melt common metals. I am still alive you see. About 30 celsius is highest temperature I ever felt from a sun. I am asking this:
If sun is at its highest possible temperature in my area, let's say it's 40 degree celsius, and if strongest laser on planet are compared over same area or object, who is stronger? Or if both are over same lense.
Simple question.

Or simply, what will take less space to build if i want to melt metals using light? Sun or some artificial device like laser? I read already about solar furnace, but that one which gives 4000 celsius looks big. Will laser give smaller?
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[*] posted on 8-4-2018 at 15:20


I wonder how intense sunlight would be if you took into account the inverse square law and measured it from a short distance out from the surface of the sun?
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[*] posted on 8-4-2018 at 15:43


As others have said, you're conflating energy per unit area with energy alone. The Sun puts out an absolutely staggering amount of energy compared to anything humans have ever built, but because it's all emitting radially outward and we're quite far away, the amount that reaches you specifically is lower than anything a laser, torch or furnace might output were you to get near one.

Therefore, the answer to your question largely depends on the melting point, size and mass of whatever you're trying to melt. If it's just a tiny bead of aluminum, no bigger than the size of a pea or so, a Fresnel lens and a good sunny day should be fine. But if you're trying to operate a larger-scale furnace or trying to melt things like stone or ceramic, I would imagine other approaches to be a better use of your time.




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[*] posted on 8-4-2018 at 16:07


On the youtube channel "king of random", there are a few videos where Grant uses a screen from a projection tv (which shouldn't be too hard to find these days). Check it out, he melts glass, concrete, and quite a few metals with it. Hard to beat with a homemade laser, for myself at least.
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[*] posted on 8-4-2018 at 23:14


Just for fun I thought I'd work out the power flow from a "cooking pot" at 4000C, assuming an emissivity of 1. If the "cooking pot" is approximated by a 20cm sphere then the surface area is about 0.5 m^2.

At 4273K the heat radiated form the pot works out to 9.45 megawatts (Stefan - Boltzmann equation). So you would need that much power input to account for radiated loss alone, in order to reach 4000C (thermal equilibrium). In sunlight terms (@1000W/m^2) that would require a mirror of 9,000 m^2, focused to a 20cm spot - which I'm not sure is even optically possible. Or you'd need a ridiculously high powered laser. Maybe the NationaI ignition facility would let you play with theirs?

Even reducing the emissivity of the cooking pot to something slightly more sensible, the power involved is still crazy.

Maybe try heating something smaller - much smaller.



[Edited on 9-4-2018 by Twospoons]

[Edited on 9-4-2018 by Twospoons]




Helicopter: "helico" -> spiral, "pter" -> with wings
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Tsjerk
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[*] posted on 9-4-2018 at 03:17


Am I correct when I say a perfectly black object, hovering in a vacuum will reach the temperature of the surface of the sun, when exposed to sunlight? In theory.
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[*] posted on 9-4-2018 at 04:09


Quote: Originally posted by Tsjerk  
Am I correct when I say a perfectly black object, hovering in a vacuum will reach the temperature of the surface of the sun, when exposed to sunlight? In theory.

No. It will give off black-body radiation.




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[*] posted on 9-4-2018 at 04:18


It’ll give off radiation, but won’t it reach equilibrium? Reaching a certain temperature through absorption whilst preventing it from continuously gaining energy through radiation.



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[*] posted on 9-4-2018 at 04:24


If the object to be heated was inside a large perfectly mirrored sphere,
with a hole just large enough to illuminate the object,
then I think that the object temperature would approach the observable temperature of the Sun.





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[*] posted on 9-4-2018 at 04:58


@Sulaiman; I think that was the theory I was after.
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[*] posted on 9-4-2018 at 05:03


Come on, people. If that were true, then all planets like would be suns. Maybe not all because some block light from coming to others, but at least then Mercury would be. Then you have to consider that these hot planets would radiate their energy to colder ones, so they will never be of the sun temperature. :cool:
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