B Is Infrared Light Invisible to Humans Due to Eye Limitations?

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Infrared light is invisible to humans because our retinas contain cone cells that are sensitive only to a limited range of wavelengths, specifically not extending into the infrared spectrum beyond 750nm. The light from the sun encompasses a broad spectrum of wavelengths, but human vision is restricted to a small portion of that spectrum, primarily in the visible range. Different animals can perceive other parts of the spectrum due to variations in the proteins present in their eyes. This limitation in human vision is a result of evolutionary adaptations. Understanding these concepts enhances knowledge of both physics and biology.
gehrenfeld
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I am 74yo and love Physics.
If my basic knowledge of physics is correct, light is a photon.

My question is:
1. Is the reason we cannot see infrared light because the spectrum travels at a wave link our eyes cannot see?
2. Does the light from the sun have all the different waves combined, and we only see one frequency, or are all the waves separate?

I hope my question made sense.
 
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Thank you.
I learned a great deal from those articles.
 
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More specifically, the reason we can't see infrared is because our retinas have cone cells with proteins that are sensitive to a small range of the spectrum, and they are not stimulated by light in the IR range. (off the right side of the graph - wavelengths > 750nm):

1650229552276.png

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

This explains why some animals can see in other parts of the spectrum - they have different proteins.
 
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