How do you assure that you are proposing a video system that will do everything that your customer wants, including recording clear images in all types of light, without running up the cost? Day/night cameras can be a dilemma. When do you propose them and when are they not required? What setting guarantees you get the best image clarity when using them? Are there different variations of day/night cameras on the market? What criteria do most of them meet? What else do you need to propose as complementary products when using day/night cameras? This month, we address all these questions and more as we demystify the technology.
Know the functionalities
Day/night cameras are capable of providing usable images at night by changing camera parameters to work more efficiently in low light. A basic example of day/night operation is the use of infrared (IR) LEDs within the camera housing. Although people can see only visible light, security cameras see both visible and IR light. The addition of artificial IR illumination enhances the ability of the camera to record an image without giving away the camera's presence or field of view.
As security cameras use color filters (blue, green and red) to create a color image, each filter allows IR light to pass through onto the sensor, muddying the colors. Since most lenses are designed for visible light only, most security cameras have an IR filter to block the IR light. This filter improves both the color fidelity and sharpness of the image.
Some lower cost day/night cameras (like those with IR illumination built into the camera housing) generally use software to create the best image they can, given the limitation of allowing both visible and IR illumination through the pixel color filters. At night, the algorithm changes, giving a slight improvement to dark image recording. Changes include desaturating the colors to give the viewer a black and white image.
Technology advances inside cameras have helped aid lighting needs. More sophisticated cameras-those cameras considered true day/night-can physically remove the IR filter from the light path, allowing the camera to see both visible daylight and IR light. This can make the camera 15 to 20 times more sensitive at night compared to a standard day-only camera. These cameras require day/night lenses to keep the scene in focus both day and night. Day/night lenses are generally more expensive because of the added complexity of focusing a broader color spectrum (from visible through IR) onto the sensor. However, show your customer the difference and the price will seem minimal compared to the benefits.
Defining a true day/night camera
A true day/night camera has a movable IR filter. During day performance, the IR filter is in place blocking all the IR light, creating a nice color image. In this case, the IR filter (represented in brown on the chart) will block all IR light greater than about 750 nanometers wavelength. At night, when light decreases, the IR filter is replaced with a clear glass dummy filter. The clear glass allows all available visible and IR light to reach the sensor and be recorded. Nonetheless, there can still be some dark corner images, which are caused by the IR illumination level dropping off as the camera moves farther away from the illumination. Although removing the IR filter improves the light sensitivity, it does so at the expense of color fidelity. To counteract the degraded color in night mode, the software for most day/night cameras desaturates the colors, creating a monochrome image.
How do you know when your customer needs a day/night camera? If there is enough visible light in the scene, a standard camera with IR filter can be used for night security applications. Illumination sources (referenced later in this text) may provide sufficient visible light. As a result, use of a day/night camera in night mode may not be necessary. In this case, the use of a day/night lens is optional. When there is adequate visible light at night, a non-day/night lens can be used with a standard, non-day/night camera. Just make sure that the lens can support the number of megapixels in the camera.
Pick the right lens