Capital & Recurring Costs: The cost of lighting includes up-front capital costs as well as recurring expenses. The ratio is approximately 8 percent capital, 4 percent maintenance (cleaning and bulb replacement) and 88 percent electrical costs. Obviously, the efficiency, or efficacy of the lamp (measured in lumens per watt) and its life expectancy has a large impact on the overall cost of lighting. The table below provides comparisons between different types of lamp efficacy and expected life (there are 8,760 hours/year, 8 hours/day is 2,920 hours/year).
Depending on the operating environment, cleaning of lamps is important since dirt will reduce the efficacy of a lamp by 5 percent per year in an office and 20 percent per year in an industrial environment. Aging of the lamp can also reduce its efficacy by up to 20 percent during its lifetime.
Lighting Levels and Security
While it is difficult to identify the direct correlation between nighttime artificial light levels and crime levels, studies in Crime Prevention Through Environmental Design (CPTED) show that criminal activity is less prevalent in open, well-lit areas.
A study by Rensselaer Polytechnic Institute (RPI), published in 1996, measured the "sense of security" felt by people in response to the implementations of different lighting designs in various environments, such as the exterior of a garden apartment complex, a loading dock area and retail parking. The qualitative findings were that installations with increased lighting levels and improved lighting uniformity produced a higher "sense of security" and, in some cases, more cost efficient lighting.
Lighting and Video Cameras
Faceplate Illumination: Of the light that is reflected from an object being viewed, some is absorbed by the lens of a camera before arriving at the sensing element. Most camera manufacturers will specify the light sensitivity or minimum illumination, in lux or footcandles, required at the camera faceplate to produce full or usable video, given a lens with a particular f-stop. If the actual lens being used has a higher f-stop, less light will be available at the image sensor. If you are in any doubt about the available light for a camera application, it makes sense to request a demo unit and test it in the actual environment that it will be used.
Megapixel Cameras: Megapixel cameras are a boon to many security applications and are needed to save us from the embarrassment of the low-quality images from convenience store hold-ups that appear on the nightly news. However, the image sensors in megapixel cameras require a higher intensity of light than conventional cameras to excite all of the pixels, and the lens needs to be of much higher quality. Be aware and ensure that the correct light levels and accessories are specified to maximize the megapixel camera's performance.
Low Light and Video Motion: Another essential for adequate light levels is where camera image display and recording is being initiated by video-analyzed motion detection. When the level of natural or artificial light decreases - day passing to night or interior lighting being reduced on a timer or by a standalone motion detector - the camera element may still receive enough light to produce a snowy or pixilated image; the "snow" may be interpreted by the camera as motion so that the image is recorded at all times and "real" motion alarms are lost - along with your video storage budget!
Glare and Light Contrast: Video sensing elements do not normally handle high contrast in lighting as well as the human eye can. Where we may be able to filter out the sunlight glaring off of the lobby marble floor, the camera may be blinded. Obviously, the best option is to locate and align the camera so that it does not suffer from this problem, however, in some applications, high contrast is inevitable. Select a camera that has offers a wide dynamic range and, as noted for megapixel cameras, if in doubt, test it out!
Infrared Cameras: As noted earlier, camera sensing elements are able to "see" further into the infrared (IR) band of the electromagnetic spectrum than our eyes can. Some cameras are designed to sense only infrared energy and produce monochrome images that show the heat emitted by hot bodies. Humans, animals and vehicles can be clearly differentiated from surrounding grass and foliage.
An alternative is to shine IR light on the surveillance area, and there are a number of cameras that include built-in IR-emitting LEDs. Standalone IR lighting fixtures can also be focused on the scene. Using this lighting technology, nighttime surveillance becomes covert since we cannot see the light. An added advantage is that light trespass is no longer a problem.