What main wavelengths are within sunlight (p.s. not a hw problem)

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    Sunlight Wavelengths
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Discussion Overview

The discussion revolves around the main wavelengths present in sunlight and their effects, particularly in relation to the use of large Fresnel lenses. Participants explore the contributions of different parts of the electromagnetic spectrum, including visible light, ultraviolet, and infrared, to the energy output of sunlight and its interaction with materials.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about which wavelength contributes most to the energy from sunlight, suggesting visible light, ultraviolet, infrared, or potentially others.
  • Another participant asserts that visible light is the primary wavelength, noting that materials are likely optimized for this region.
  • A question is raised regarding the effectiveness of polished aluminum versus an aluminum-gold alloy for reflecting sunlight.
  • One participant mentions consulting an optical engineer who claims that the energy primarily comes from the infrared spectrum, though they express skepticism about this due to the perceived weakness of that wavelength.
  • A later reply supports the optical engineer's assertion, stating that most radiant heat from the sun is indeed in the infrared spectrum.
  • A participant questions whether the high temperatures generated by the Fresnel lens result from infrared or visible light, seeking clarification on which wavelength is responsible for temperature changes.
  • Another participant emphasizes the importance of considering the material being heated, noting that different materials absorb light differently across wavelengths, particularly in the infrared and visible regions.
  • A follow-up question is posed about materials that do not heat up in the infrared and visible wavelength spectrum.

Areas of Agreement / Disagreement

Participants express differing views on the primary wavelengths contributing to sunlight's energy, particularly regarding the roles of visible light and infrared. There is no consensus on which wavelength is most significant, and the discussion remains unresolved.

Contextual Notes

Participants highlight the dependence of heating effects on the material properties and absorption characteristics, indicating that the discussion is influenced by these factors.

rasgar
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I ordered these giant fesnel lenses online. They are about 2.6 by 3.3 feet, and can supposedly melt asphalt. I was just wondering what is the main wavelength that causes the energy: visible light, ultra-violet, infrared, some other that I don't know about, or all of them?
 
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So would polished aluminum be the best for reflecting it, or would some aluminum-gold alloy be more effective in reflecting it?
 
I talked to an optical engineer, and she said that the energy came from the infrared spectrum, but it doesn't seem to make much sense since its a weak wavelength.
 
rasgar said:
I talked to an optical engineer, and she said that the energy came from the infrared spectrum, but it doesn't seem to make much sense since its a weak wavelength.

But she is right. The majority of the radiant heat from the sun is in the IR spectrum.

Zz.
 
So the high temperature that the fresnel lens can generate is from infrared or visible light (i.e. which one could cause that temperature change alone)?
 
rasgar said:
So the high temperature that the fresnel lens can generate...
"Generate" in what object? That's one aspect of the problem to keep in mind as well. Different materials will absorb more light from different wavelengths. Most solids have absorption peaks around the IR and visible regions. How quickly you can heat up a thing with specific wavelengths depends on what the thing is made of.
 
Gokul43201 said:
Different materials will absorb more light from different wavelengths. Most solids have absorption peaks around the IR and visible regions. How quickly you can heat up a thing with specific wavelengths depends on what the thing is made of.

Out of curiosity, does anyone have any examples of a material that does not heat up in the IR and visible wavelength spectrum?
 

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