One of the biggest problems with camera systems has always been producing viable, working images in the dark. I'm not just talking about low light, I mean in the dark. Yes, we have had the technology to look around in the dark for the past 30 years, but could we afford it, and could we do it in color? Let's start with a quick overview of the problems that face image production in the dark.
In the Dark
The first step is to understand how a camera sees. It produces an image the same way the human eye does. We take the reflective light from a scene and focus it on the imager, which is made up of several light-sensitive points (pixels). The imager creates an electronic pattern in response to the highlights and colors. Simple.
The first mistake most designers make is measuring the ambient light in an area and considering that measurement to represent the light the camera uses. However, cameras see reflective light as well, so with only an ambient light measurement, we come up anywhere from five percent to 95 percent short in our lighting. For example; if the ambient light at the darkest point in a parking lot is .01 foot candle (fc), we must remove 95 percent of that to determine the actual working light of the camera, because asphalt has a five percent reflectivity. The consequence is that we really have .0005 fc of usable light in that parking lot at night.
Light loss caused by the lens is another impact that may be missed. Light loss from the lens can be as much as two to three f-stops. An f-stop is a unit of measurement assigned to light gain or loss. One f-stop gain is equivalent to a 50 percent decrease in light, and one f-stop down is equal to a 100 percent gain in light. Therefore, if our lens has a two f-stop light loss factor, we must decrease our .0005 fc by 50 percent two times (once for each f-stop): .0005 fc / 2 = .00025 fc / 2 = .000125 fc. Now we don't have to know what a fc of light is to be able to understand that there is a huge difference between the original ambient light measurement of .01 fc and the final .000125 fc.
Our dilemma lies in the lack of useable reflective light for the camera and the lack of color reflectivity below 2 fc of ambient light.
Options and Pricing
A short five years ago, our options in the above situation were limited. We had four choices:
1) Use a black /white (BW) camera with good sensitivity.
2) Use an intensified camera (also BW)
3) Use an infrared enhanced lighting scheme with an IR-sensitive camera (also BW)
4) Use a thermal camera (no color orientation).
Five years ago, the sensitivity range for a BW camera directly corresponded with the price. The higher the sensitivity, the higher the cost of the unit. But BW cameras were still the most affordable cameras, ranging from $800 to $1,200 for up to .0001 fc. The intensified camera of the past averaged between $8,000 and $12,000 without housing or lens and averaged a sensitivity of .00002 fc (half moonlight).
The IR-enhancement light scheme would include one or two large, expensive IR lamps with a potentially expensive camera. As a set, the average IR lamp/camera would cost about $3,000 to $5,000 complete.
The thermal camera of five years ago started at around $50,000 and could work up to $300,000 very quickly (dependant upon lens and image enhancements). The sensitivity of the IR-enhanced and thermal cameras is a moot point, because the IR camera uses IR light enhancement as an aid and the thermal camera does not recognize light.
So what's so exciting about the market today as opposed to just a few short years ago? Everything!
Color at night. We are quickly realizing color at night. The new color cameras are toting sensitivity ranges as low as .003 fc. This is a huge improvement over the sensitivity of previous versions, and it is literally changing many, if not most of our night views. The door to color at night is wide open and applications are streaming in.