Absorption of light in a mirror

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Discussion Overview

The discussion revolves around the absorption of light by mirrors, specifically addressing whether mirrors can be considered 100% reflective and what types of light they absorb. The scope includes theoretical considerations of reflectivity and material properties of mirrors.

Discussion Character

  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants assert that no mirror is 100% reflective, implying that all mirrors absorb some amount of light.
  • One participant questions the logic of a mirror being 100% reflective while also absorbing light, seeking clarification on the nature of absorption.
  • Another participant explains that mirrors can absorb a little bit of all wavelengths and that different materials enhance reflectivity for specific parts of the electromagnetic spectrum.
  • It is noted that aluminum is commonly used for visible light mirrors due to its significant reflectivity in that range, while gold is preferred for near-infrared light.
  • A participant mentions that the appearance of mirrors can vary, with some looking greenish, indicating differential absorption of wavelengths.

Areas of Agreement / Disagreement

Participants generally agree that mirrors are not 100% reflective and do absorb some light, but there is no consensus on the implications of this absorption or the specifics of what is absorbed.

Contextual Notes

The discussion includes varying interpretations of reflectivity and absorption, with references to specific materials and their properties, but lacks a definitive resolution on the nature of absorption in mirrors.

richardz03
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I read in some place that the mirror be it 100 per cent reflective, will also absorb if a light strikes to it. Is it true? what does it absorbs?
 
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No mirror is 100% reflective, so yes, some amount of light will be absorbed no matter what. A perfectly reflective mirror would, by definition, reflect 100% of the light and absorb none. But these do not exist.
 
Drakkith said:
No mirror is 100% reflective, so yes, some amount of light will be absorbed no matter what. A perfectly reflective mirror would, by definition, reflect 100% of the light and absorb none. But these do not exist.

Ok but what does it absorbs? does it absorbs all the color a little bit or something else happens
 
richardz03 said:
I read in some place that the mirror be it 100 per cent reflective, will also absorb if a light strikes to it. Is it true? what does it absorbs?

This doesn't quite make any sense, does it? If it is 100% reflective, then there is no absorption.

What exactly are you asking here? Are you asking on what happened to the light that is not reflected in a typical mirror? Or are you asking for something else?

Zz.
 
It will absorb a little bit of all the wavelengths. Mirrors can be made from many different materials to enhance their reflectivity of certain parts of the EM spectrum. For example, mirrors designed to reflect near-infrared light are typically made of gold because it reflects a larger portion of near IR light than most other kinds of mirrors. Aluminum is typically used to make visible light mirrors since it reflects a significant portion of visible light that falls on it, but will reflect less of other types of EM radiation such as UV or IR (it's also much cheaper than most alternative materials).

See the graph below, which comes from here: http://en.wikipedia.org/wiki/Reflectivity

400px-Image-Metal-reflectance.png


As you can see, the amount of light reflected (measured by the Y-axis) changes depending on the wavelength and the type of mirror. Note that visible light has a wavelength between 400 nm to 700 nm. In this range the aluminum (Al) mirror reflects more light than the other two. Gold (Au) and silver (Ag) reflect more light in the near-IR range which is the right half of the graph.
 
Just FYI, posts from another thread have been merged into this one.
 
Drakkith said:
As you can see, the amount of light reflected (measured by the Y-axis) changes depending on the wavelength and the type of mirror. Note that visible light has a wavelength between 400 nm to 700 nm. In this range the aluminum (Al) mirror reflects more light than the other two. Gold (Au) and silver (Ag) reflect more light in the near-IR range which is the right half of the graph.
Aluminium also reflects different wavelengths more evenly, so the reflections appear in the same colors as the original.

As seen from the side, mirrors often look greenish, revealing that they are not perfect mirrors but absorb different wavelengths a bit differently.
 

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