Why Reflected Light from a Mirror Does Not Get Absorbed by Polarized Sunglasses

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Light is light; neither the light nor the glasses care about whether the light has been reflected off of a mirror. However, understanding the behavior of reflected light and its interaction with polarized sunglasses can provide insightful knowledge. This article explores the science behind why reflected light from a mirror does not get absorbed by polarized sunglasses and explains the underlying principles of light polarization and its interaction with different surfaces.

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The Basics of Light Polarization

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Light can be described as a wave with both electric and magnetic components oscillating perpendicularly to the direction of propagation. Polarization refers to the orientation of these wave components. Unpolarized light has wave components oscillating in all directions randomly. When light passes through a polarized filter, only the components aligned with the transmission axis of the filter are allowed to pass through, while those aligned perpendicularly are absorbed.

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Polarized Sunglasses and Light Absorption

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Polarized sunglasses work by absorbing light waves oriented perpendicular to the transmission axis of the lens, typically oriented vertically. Unpolarized light contains both horizontal and vertical components, and since the axis of the lens is vertical, only the horizontal components are absorbed. Thus, half of the light is absorbed by the lenses.

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Reflection from Metallic Surfaces

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When light reflects from metallic surfaces, such as the mirror, the light is not polarized to any significant degree. According to Malus's law, the intensity of reflected polarized light can be reduced through a polarizer if the polarization axes of the reflected light and the polarizer are not aligned. However, since the light from a mirror is not polarized, it will have both polarized and unpolarized components. Therefore, half of the light from a mirror will pass through a Polaroid lens, despite the fact that the light is reflected and would, in theory, be polarized.

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The Role of Brewster's Angle

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Brewster's angle is a condition under which unpolarized light is completely polarized upon reflection from an interface. If light is reflected from a surface at an oblique angle, the reflected light becomes polarized horizontally. Therefore, if light from a reflective surface at Brewster's angle is incident on the polarized lens, it can be fully absorbed, as the lens is typically designed to absorb light polarized horizontally.

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Practical Implications

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Practically, the behavior of reflected light from a mirror and its interaction with polarized sunglasses can be seen in everyday scenarios. For example, when light reflects off a flat mirror, it is not polarized and thus contains half polarized and half unpolarized components. When this light hits a vertically polarized lens, half of it will pass through, and half will be absorbed. This phenomenon helps explain why some surfaces, such as smooth mirrors, do not significantly affect the effectiveness of polarized sunglasses, and why other surfaces, like water surfaces at specific angles, can be highly effective.

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Conclusion

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In summary, while reflected light from a mirror does not get significantly absorbed by polarized sunglasses, this behavior is due to the lack of polarization in the reflected light. The angle of reflection, surface properties, and the orientation of the polarized lens all play crucial roles in determining the fate of the light passing through the lens. Understanding these principles not only enhances our scientific knowledge but also helps in designing more effective optical materials and devices.