Day-Night IP surveillance cameras are quite common today and can display images based on reflection of IR light (invisible to eyes, but picked up by camera sensors) from near-infrared (IR) spectrum. Then there are Thermal IP surveillance cameras that can display images using reflected heat (thermal radiation) in total darkness. So if you want to monitor your facilities in low-light or night, you can do it with IP surveillance cameras.
Day-Night IR Surveillance Cameras:
With visible light images are produced when the eye sees the reflected light from an object. But visible light is a small part of the electromagnetic spectrum (wavelength range: 400 to 700 nm). The intensity of visible light is measured in Lux – Lumens per Square Meter.
But the electromagnetic spectrum extends beyond the visible light. Day-Night IR surveillance cameras can see and record images using the reflected near-infrared (IR) rays instead of visible light. The near-infrared spectrum extends over wavelengths of 700 to 1100 nm. It measured in mW per square meter.
The Day-Night IR surveillance cameras require some light source to function effectively and cannot work in pitch darkness. Most of them produce black and white images, but some of them can produce colored images as well using color corrected illuminators. But these are mostly restricted to scientific applications as the scope of error with them is higher.
For places that become totally dark during nights, either an artificial white light based illuminator could be used (or) an IR illuminator that can produce near-infrared light (which is invisible to the human eye) can be used. In most cases, the latter option is used for night vision surveillance. These illuminators, either integrated with the camera or used as a separate unit, enhance the images in extreme low-light/night conditions. An IR illuminator can illuminate larger spaces than normal light at similar power levels.
These Day-Night Cameras use IR Cut filter in the day in order to record normal color images reflected by white light. This filter disallows IR waves. But during the night the IR Cut filter is automatically removed and black & white images are recorded based on IR reflections.
Thermal IP Surveillance Cameras:
While Day-Night Cameras can be used for detection and identification of objects in low-light conditions, Thermal IP Surveillance cameras can be used for detection of objects in nil (or) zero darkness conditions. It will enable you to recognize that someone is passing through a secured area but not who.
This is because Thermal cameras detect and use the thermal heat (radiation) emitted by a body/material to produce images. These images are a function of the temperature of the body and all materials emit some degree of heat. Hotter bodies emit more thermal radiation and colder bodies emit lesser thermal radiation. The varying temperatures are represented by varying colors to produce a negative like image (digitally) using Thermal Cameras that use germanium or similar alloys to block the visible light and allow thermal radiation (instead of glass).
Thermal cameras are quite expensive and are used in specific applications like military, securing high net-worth places (like oil fields), sensitive national boundaries, etc. Thermal cameras perform well under total darkness, fog, rain, smoke, haze and other such vision inhibitors as they are not based on reflected light.
There are different types of Thermal cameras. Some of them use cryogenic cooling at very low temperatures for producing clearer images, but they are very expensive to buy and maintain. Some of them use micro-bolometers which still require some cooling. There are other thermal cameras which use uncooled thermal image sensors. The third category of thermal cameras are popular for enterprise surveillance applications as they are relatively less expensive and can last for years without extensive maintenance.
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