Neogonodactylus said:
The blue LED's have a very narrow spectral range peaking at around 470 nm, the same wavelength that you woud find at depths below 30 m in the middle of the day. It is also fairly close to the peak sensitivity of most octopus that have been studied.
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Moon light will have he same spectral qualities, but would be much dimmer. I agree that a tank shimmering in blue light is appealing to our human senses, but it probably seems pretty bright to your favorite octopus.
Very good point-- it's really coincidental that monochromatic blue LEDs happen to look to humans similar to moonlight-- I'd even argue against moonlight having the same spectrum-- it's just blue-dominated, but broad spectrum (reflected sunlight), while the LED is literally photons of only one wavelength. (although white LEDs are really 3 LEDs in one package, so they're 3 distinct single wavelengths). When SCUBA diving, actually, I've noticed I get the same sorts of color-reduction effects as I do in moonlight, for similar reasons... in fact, I like having a small dive light even during the day to illuminate reef bits with full-spectrum light.
It's sometimes hard to remember how differently animals' visual systems are set up to perceive the world, and assume everything sees like we do... even when it's "as different as night and day."
This all made me think of a Moody Blues song/poem:
Cold hearted orb that rules the night,
Removes the colors from our sight.
Red is grey and yellow white,
But we decide which is right.
And which is an illusion?