Day & Night Vision, Infra-red Capability
Article updated and as presented in CPD seminar in Feb 2012 in Compucon House
Day Vision refers to the operation of a camera under normal daylight conditions, whereas Night Vision refers to night time when the intensity of visible light is low such as 1Lux. When there is no visible light, the camera will have to rely on Infra-red (IR) for seeing. However, if the camera is stated as Day & Night but with no mentioning of IR, we must not assume it has IR capabilities.
Infrared is a term used in many areas such as for controlling a wireless mouse or TV channel selection. Many people ask for Infrared when requesting prices for a video surveillance system as a habit. We shall find out about this magic term Infrared (IR) but would like to confine the scope to physical security only plus a bit of scientific data for support purposes.
The simplest use would be in Passive Infrared (PIR) sensors which many organisations have installed for detecting intruders. Human body has a temperature of around 36.8 degree Celsius and the body emits radiation of a certain Infrared wavelength at all time (yes this is true). By detecting this particular wavelength, the sensor determines if there is a human intruder by the presence or absence of this particular wavelength in the area under surveillance.
A video surveillance camera can add such a PIR sensor to the camera body as a separate device to the lens. Many cameras cannot see in darkness whereas the PIR sensor does not need visible light. The camera or its recording software can include an algorithm for recording motions only when confirmed by the PIR sensor during dark times. When the PIR sensor detects human motion, the camera or its recording software can turn on lighting to facilitate recording. This is achieved via a Digital Output port that most modern IP cameras are equipped with.
The next development is to include Infrared (IR) LED in the camera such as on the outside circumference of the lens. These LED will emit Infrared when darkness is detected and stay inactive in daytime under the control of a sensor. The emitted Infrared is not visible light as Infrared is not visible to the human eyes. It can record in black and white only (not in colours). The distance of surveillance covered by such a camera would be limited as this depends on the strength of the installed LED. When its manufacturer claims 30 metres, we can expect 30 metres to be marginal. As far as the recording mechanism is concerned, the camera can be set to the same criteria whether it is in daylight on visible light or in darkness on IR.
If we want to cover a longer distance of surveillance, employing an external Infrared Illuminator would be the best way to go. This is because cameras integrated with IR LED have fixed IR LED suitable for a certain distance and angle of view only. An external IR illuminator provides choices and allows the best fit for purpose. We need to verify that the distance and angle of view covered are aligned with the camera and our requirements.
There is in fact another IR related camera surveillance capability called IR filter cut-off. This capability does not relate to any IR LED or illuminator at all. It is an electronic implementation within the camera to filter off IR during daytime especially when the day is transitioning to night. When the visible illumination is low, IR that exists in the environment will become noise to the camera and render low illumination images lesser clear. Do not assume that all cameras have this capability.
IR covers quite a large part of the spectrum of electromagnetic waves. It has a smaller wave frequency than visible light which consists of red at its lowest frequency border and violet at its highest border. Scientists have broadly and artificially separated IR into 3 ranges: Near, Mid, and Far. The above discussions relate to Near IR only.
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