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When seen from below by a predator, the animal's light helps to match its brightness and colour to the sea surface above. Counter-illumination is a method of active camouflage seen in marine animals such as firefly squid and midshipman fish, and in military prototypes, producing light to match their backgrounds in both brightness and wavelength.
Currently issued in the USMC, the AN/PEQ-16B helps to consolidate the number of attachments on the hand guards of infantry weapons, including the visible, and infrared lasers, an infrared illuminator, and a white-light illuminator for urban or dark environments where night vision devices may be impractical or not available.
Large lenses can gather and concentrate light, thus intensifying light with purely optical means and enabling the user to see better in the dark than with the naked eye alone. Often night glasses also have a fairly large exit pupil of 7 mm or more to let all gathered light into the user's eye.
An NVD image is typically monochrome green, as green was considered to be the easiest color to see for prolonged periods in the dark. [2] Night vision devices may be passive, relying solely on ambient light, or may be active, using an IR (infrared) illuminator. Night vision devices may be handheld or attach to helmets.
Photophores on fish are used for attracting food or for camouflage from predators by counter-illumination. [ citation needed ] Photophores are found on some cephalopods including the firefly squid , which can create impressive light displays, as well as numerous other deep sea organisms, such as the pocket shark Mollisquama mississippiensis and ...
Fossilised skin pigmented with dark-coloured eumelanin reveals that ichthyosaurs, leatherback turtles and mosasaurs had dark backs and light bellies. [21] [22] The ornithischian dinosaur Psittacosaurus similarly appears to have been countershaded, implying that its predators detected their prey by deducing shape from shading. Modelling suggests ...
This increases the amount of light each photosensitive cell receives, allowing the bird to see better in low light conditions. [4] Owls normally have only one fovea, and that is poorly developed except in diurnal hunters like the short-eared owl. [77] Besides owls, bat hawks, frogmouths and nightjars also display good night vision.
Predators need not locate their host directly: Kestrels, for instance, are able to detect the faeces and urine of their prey (which reflect ultraviolet), allowing them to identify areas where there are large numbers of voles, for example. This adaptation is essential in prey detection, as voles are quick to hide from such predators.