Posts Tagged ‘ Lux ’

Infrared CCTV Camera

Thursday, September 15th, 2011

Infrared CCTV cameras are becoming one of the most popular types of security/surveillance cameras for residences and commercial applications alike.  Before purchasing an infrared CCTV camera it’s important that you are familiar with some of the terminology and functions associated with this specialized aspect of a CCTV security system.

Most Closed Circuit Television or CCTV cameras today are digital cameras.  Basically, they take pictures or video much the same way as a personal digital camera or camcorder.  These cameras operate by allowing light to penetrate through an iris or variable opening, a lens, and then strike a Charged Coupled Device or CCD or a Complementary Metal Oxide Semiconductor or CMOS.

The iris is basically like the pupil of an eyeball; when there is too much light the iris makes the opening in the lens very small so as not to “flood” the CCD with light.  When there is very little or no light, such is the case for night vision security cameras, the iris is at its maximum opening to allow as much available light as possible to strike the CCD.

The chief purpose of the lens is to keep an image at a certain distance in focus.  Various lens sizes can be used to achieve focus ranges from just a few feet to several hundred.  If the lens is rated with an “F-Stop” the lower the number for night vision purposes is better because it means it does not absorb much of the light passing through it.

The key to an infrared CCTV camera is the CCD or CMOS.  CCDs and CMOSs work by converting light into electrons.  These electrons have a charge which can be monitored and used to produce a digital image.  Both sensors are inherently sensitive to infrared (IR) radiation.

There are basically two types of security cameras used as night vision security cameras.  It’s important to understand the difference between the two.  One type is also called a day/night camera and the other is an IR camera.

Day/night cameras produce color images when sufficient light is present.  These cameras have very sensitive CCD or CMOS chips that allow the camera to process light into an image at very low light intensity.  Light intensity is normally measured in units called LUX.  In full daylight (but not direct sunlight) an average LUX reading ranges from 10,000 to 25,000 LUX.  By contrast, a full moon on a clear night in non-tropical geographical locations produces about .27 LUX.  Many day/night cameras can produce clear images at less than 1 LUX.  In fact some day/night vision security cameras’ specifications indicate sensitivities as low as .0014 LUX or less.  However, day/night cameras must have at least some available light to produce an image.  They cannot produce an image in total darkness or 0 LUX.

Night vision security cameras that can produce images in 0 LUX or no-light conditions are infrared CCTV cameras.  These cameras can “see” infrared radiation in the 700 – 1400 nanometer wavelength range known as “near infrared.”  The human eye cannot see this wavelength of electromagnetic radiation so any “near infrared” light is virtually invisible to our eyes.

Infrared CCTV cameras using IR technology illuminate their target area with infrared light.  This light is provided by light emitting diodes or LEDs that are placed around the lens of the camera.  The stronger the LEDs and the greater number of LEDs placed around the camera lens determines the effective range and field of vision of IR cameras.  In essence, the LEDs are actually providing a spotlight on the target area but because the light is the near infrared type we (humans) cannot see it.

Infrared CCTV Cameras using IR technology produce a black and white or monochromatic image.  This radiation is outside the visible color spectrum therefore the images are not in color.  However, the clarity and contrast is just as sharp as normal color images.   Also, the range of the infrared night vision security camera is limited by the infrared light produced by the LEDs.  Most premium IR cameras have an effective operating range of up to about 150 feet.  It’s imperative to know the specification for IR range when purchasing an IR camera as a camera with a very short range would be useless for monitoring an area 100 feet from the camera.

Knowing a little about the two types of night vision security camera can help you make the right choice for your needs.


What is a LUX Rating?

Wednesday, March 31st, 2010

Security cameras usually have a LUX rating. This LUX rating is the actual available light intensity at which the camera can produce a picture.

A LUX, abbreviated lx, is the International System of Units (SI) measure of the intensity of light. It can be thought of as the strength of light as determined by the human eye. A LUX is based on another unit of light measurement called a lumen, which is based on yet another unit called a candela. In the United States, the non-SI unit to measure light intensity is the footcandle. One foot candle is approximately equal to 10.8 LUX.

In order to put things in perspective, here some are some setting examples with their equivalent LUX rating:

• A quarter moon-lit night produces about .01 LUX
• A full moon on a clear night produces about 0.27 LUX
• A full moon on a clear night near the equator produces about 1 LUX
• An average family room produces about 50 LUX
• An overcast, dark day produces about 100 LUX
• Typical office lighting ranges from about 300 to 500 LUX
• Direct sunlight can range from about 30,000 to 130,000 LUX

The LUX rating of a security camera is based on several factors, three of which are the lens, sensor chip, and “F stop.” The lower the LUX rating of a security camera the less light is needed for the camera to produce a usable picture (video).

When considering sensor chip technology and LUX rating, there are basically two types of sensors used to produce an image, CMOS and CCD. CMOS sensors usually require a brighter intensity of light then CCD sensors and therefore cameras built with this sensor have higher LUX ratings. Generally, the greater the sensitivity of the sensor and therefore the less light needed to produce an image, the higher the cost of the camera.

In addition to sensitivity of the CCD or CMOS chip, the lens can affect the LUX rating as well. Light must pass through the lens and although a lens may appear as perfectly clear, it still absorbs some light as it passes through it. If the lens has any special filter technology, if it is unusually large, or if it is shaped in a unique way, these factors can all increase the LUX rating of the camera.

The camera has an opening or hole that the light passes through before activating the sensor. This is called the aperture or sometimes referred to as the “F-stop.” The lower the F-stop the closer to the camera the image will remain in focus. If the aperture is at a high F-stop, the objects farther away are in focus. Less light is needed for low F-stops to produce a clear image. More light is needed for a greater F-stop. Most cameras do not have a fixed F-stop per se; the iris controls the size of this opening and in most cases varies it as needed.

Most security cameras operate with a LUX rating of 1.0 or less. Some cameras have LUX ratings as low as .003 LUX. If a camera has a rating of 0.0 LUX it must be an infrared camera because a rating of 0.0 LUX means there is no available light and therefore an image can not be captured, unless it is through infrared imaging.

There are many factors that affect the LUX rating of a security camera. Talk with your professional security technician about your particular requirements. A professional security technician can help you choose the right LUX rated camera for your specific application.