Why are animals not scared off by the light from an infrared night camera?

Answer

Hi Andre,

This has everything to do with the wavelengths of light that a wildlife camera emits, and the wavelengths that our eyes (and those of (mammals) animals) can observe.

Light is a form of electromagnetic radiation, which means that you can imagine it as a packet of energy (a photon) that moves in an undulating motion.

The human and animal eye contains cells that are stimulated by photons. They pass that stimulus on to our brains, where the stimuli from those approximately 100 million cells are received, and an image is formed with them.

However, those cells are only sensitive to photons of a certain wavelength: some are only stimulated by photons with a wavelength of 400 to 500 nanometers (nm for short, which is 400 to 500 millionths of a millimeter), while others are stimulated by photons with a wavelength of 500 to 600 nm or 500 to 650 nm are excited. In this way, our brains can distinguish the wavelength of those photons and convert that information into colour.

The shortest wavelength that our eyes can detect is about 400 nm and corresponds to violet light. All light with a shorter wavelength is called ultraviolet (UV). That light is, for example, the UV radiation that can cause sunburn. The longest wavelength is about 650 nm, and is red light. All light with a longer wavelength is called infrared (IR) and is generally very harmless. Mammals can see roughly 400-650 nm, but there are other animals (insects, fish, …) that can also detect higher or lower wavelengths.

Most wildlife cameras have a light source with infrared light (about 850 nm). Most digital cameras can detect IR light, but usually that light is blocked with a filter, because that would make invisible light visible. In a wildlife camera that filter is not there, and on the contrary, the camera is designed in such a way that it just detects the IR light. When it takes a picture, it sends out a fairly bright flash of light, but because it’s IR light, mammals’ eyes can’t see it. The camera does.

Conclusion: the animals are not afraid of the light, because the (mammal) animal eye cannot see that infrared light.

Kind regards,

Benjamin