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.
