Applicability   Photovoltaic systems are applicable to almost any function that requires low levels of electric voltage. In the landscape, this includes a wide variety of lighting needs such as area, parking, and security lighting; street and path lighting; and lighting for signage. They can provide power for a number of other applications: emergency call-boxes and for water pumps used in landscape irrigation; decorative fountains; and pumping potable water to facilities for human usage. One private company even uses solar power for an electric security fence.       In order to help people understand the environmental benefits of a photovoltaic system, the Environmental Protection Agency (EPA) has developed a "pollution prevention calculator" for carbon dioxide, nitrogen oxides, and sulfur dioxide, which are some of the most prevalent pollutants in the atmosphere. For those considering purchasing a PV system for environmental reasons, the calculator can quantify exactly how much good one is doing, and, correspondingly, if the investment is worthwhile. The calculation is based on the amount of electricity produced by a PV system, and the geographic location of the system. The calculator renders pollution reduction tangible by equating reduced CO2 emissions with the number of miles a car would have to travel to produce that amount of CO2, or the number of trees it would take to absorb that amount of CO2. To calculate carbon (C), rather than carbon dioxide (CO2), emissions, one can take the EPA's CO2 values and multiply by 0.3. For example, a PV system that prevents 10,000 lbs. of CO2 emissions will prevent 3000 lbs. of carbon emissions.