How does an IR camera work?
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Infrared light is a type of light that cannot be
seen by a person’s eyes. This is because Infrared light uses wavelengths longer
than light of the visible spectrum. Infrared illumination allows a camera to
“see” even in total darkness. It does this through the use of lamps or diodes
that emit infrared light at a specific wavelength. The two wavelengths that are
common to infrared illuminators are 715 nanometers and
830 nanometers. The human eye can see up to 780 nanometers and therefore can
faintly see illuminators that use the 715 nm wavelength. For true covert
nighttime surveillance, illuminators that operate at 830 nm should be used.
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The light produced by the bulbs is filtered so at a minimum the only
wavelengths emitted are either 715 nm or 830 nm respectively. These numbers are
starting points with regards to the frequency emitted; they are the absolute low
end of the spectrum utilized by the camera. Wavelengths lower than the spectrum
used by the camera are reflected and collected inside the IR illuminator. This
collection generates heat in addition to the heat of the wavelengths used by the
camera. If close enough, a person can thus feel that an IR camera is on even
though they cannot see the wavelengths used.
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The ability of a camera to capture a picture based
on the level of light is measured in lux. The lower the lux rating, the better
the camera can see in low light. All IR cameras have a lux rating of 0 – meaning
that they can see in no light at all. Color IR cameras
switch to B&W at night for the purposes of monitoring because of the greater
sensitivity that can be achieved this way. A photo cell inside the camera
monitors daylight and determines when to switch. Some cameras even use a lens to
disperse the IR waves. A distinction should be made between IR cameras and
day/night cameras. Day/night cameras can operate effectively in low light but
they do not come bundled with LEDs, making it impossible for them to work in no
light at all, unlike an IR camera. |
| How to choose an IR camera |
When using an IR camera for outdoor applications, it
is best to use an outdoor IR camera. Combining an indoor IR camera with an
outdoor housing will not work properly as the IR light may reflect off the glass
of the housing. Some success has been reported when the camera is placed flush
up against the glass, though. Also, one should always look at the distance
rating or range when purchasing and IR camera or illuminator. Purchasing an IR
camera for indoor use that has a greater range than the interior dimensions of
the building will overwhelm the camera and result in a washed out bright
picture. It should be noted that IR cameras cannot see through smoke. In order
to achieve this, a thermal camera must be used.
The
CVC-627 IR camera. |
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