Wondering if there is any evidence that mammals or birds eyes can detect light emitted in the infra-red? The reason I'm asking relates to the use of nest cameras to detect predators, using infra red LED light to take pictures at night. New technology allows a picture to be taken every 3 seconds, throughout the night. Clearly if these can be seen - then a mammal, or nocturnal bird could quickly learn to look for the flashes of light and find a tasty source of food...
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1$\begingroup$ they can detect it sure, just like we can feel heat from sunlight on our skin. $\endgroup$– JohnCommented Jun 28, 2019 at 12:56
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$\begingroup$ Pit vipers do but not using their eyes and they are not mammals or birds. $\endgroup$– WYSIWYGCommented Jun 28, 2019 at 13:38
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$\begingroup$ physics.stackexchange.com/questions/147746/… $\endgroup$– bandybabboonCommented Jul 28, 2019 at 17:35
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2 Answers
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This is an interesting question, and I think what you really want to ask is
How to choose near infrared LEDs that will not be visible to mammals or birds at night?
Remember:
- their eyes will be dark-adapted
- unlike laser diodes, LEDs don't emit a single wavelength, they have a spectral spread which can have long-ish tails, especially high-power LEDS used for illumination, and especially if you plot their spectrum on a log scale, which you should in this case
- a very slightly visible dim, steady dot will not be as obtrusive as a flash, so if there's a small spectral overlap, don't flash to save power.
Outdoor security cameras often have integrated near-IR LEDs to illuminate the scene. When they are not careful and choose LEDs with wavelengths too close to our visible range (I'm going to call our long-wavelength limit 720 nm, though it's quite weak until about 700 nm) you can see dim red dots around the edge of the camera.
Point your cell phone at it and you can often see them more clearly because the near-IR cut-off is not perfect.
Different species will have different photopigments and you'll have to think about both rods and cones.
It's a big job if you want to cut it close.
Since powerful LEDs for illumination can go out to 900 to 950 nm, and a good CCD with its infrared filter removed can be sensitive out there, this should be your starting point.
If the published spectrum of your 900 to 950 nm LEDs show a short wavelength tail that might be visible to some animals, you can also add a short-wavelength cutoff filter in front of the LEDs - letting most of the light through except say anything shorter than 800 nm.
After that, choose some species and search the literature for the spectral sensitivity of neurological responses rather than simple pigment absorption plots which are shown below.
You might ask a separate question in psychology and neuroscience SE about this. Those are the folks that have a century of data on vision systems of animals. A century of mice and cats and pigeons with wires coming out of their heads...
Just as an example, Figure from Imamoto and Shichida (2014) Cone visual pigments (Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1837, (5), May 2014, pp 664-673)
Fig. 4. Absorption spectra of cone visual pigments in representative animals. The spectra of cone visual pigments of human (563, 532, and 424 nm [79], [101]), mouse (511 and 358 nm [91], [97]), chicken (571, 508, 455, and 415 nm [5]), salamander (615 (A2), 567 (A1), 444, and 367 nm [65], [102], [103]), and goldfish (566, 516, 447, and 370 nm for A1, and 617, 535, 454, and 382 nm for A2 [104]) are shown. The absorption spectra of the pigments belonging to L, M2, M1, and S group are shown in red, green, blue, and violet, respectively. The spectra of pigments having A2 retinal is shown by broken lines. These spectra were generated using Govardovskii's template [105].
Just for example see Thorlabs' IR%20Mounted%20LEDs.
NOTE: if you click the option to download the Excel data you can see there is measurable light as short as 750 nm for this particular LED, which is why a filter is a good idea.
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Infrared is a fairly large part of the electromagnetic spectrum, so to get an answer best suited to your specific case, you should specify the wavelength of your LED. There is at least one study showing that ferrets (not sure if it's the best predator to worry about for what I assume is a suspended bird's nest) can see up to 920nm.
So to answer your question, yes, at least some can, but the further into the spectrum you go, the fewer there will be.
I am much less certain, however, that this would attract danger. Nocturnal predators in biomes inhabited by humans generally evolve to avoid rather than seek out artificial light sources.
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2$\begingroup$ Thank you so much TheChymera. The camera LED's are in the 950-970 nm range - so looks very likely they will be out of range of mammals... and hopefully birds too, although I'm not aware of any evidence here - just seems likely. $\endgroup$ Commented Jul 8, 2019 at 9:12
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$\begingroup$ @DamonBridge I wrote this answer before seeing your comment here. Those are peak wavelengths of the LEDs but they can have pretty broad tails - especially when designed for high power for illumination. As mentioned in the answer, you can get short-wavelength cutoff filters that won't stop most of the LEDs' power but will remove the short-wavelength tails. $\endgroup$– uhohCommented Apr 14 at 10:33