ABSTRACT
A second means of controlling intensity is through varying the amount of light that is being produced in an environment. The simple choice of a particular luminaire or lamp can produce an incredible range of lighting intensities. Lamp wattage alone can make the difference in whether you can clearly see a stage or are forced to strain your eyes to decipher the materials that may be in front of you. The distance that separates the light source from the task also plays a role in the intensity that is observed in an environment. Rooms with higher ceilings require higher wattage or more efficient luminaires than rooms with lower ceilings to produce the same amount of footcandles on a desktop. Another popular method of controlling intensity is simply by selectively turning on and off various elements of a lamp, luminaire, or circuit. In the simplest case, a lamp will be provided with two separate filaments of different capacities. In order to provide one level of brightness, power is provided to one of the filaments. To provide a second level of brightness, power is provided to the other filament, and for maximum brightness, power is provide to both filaments. This is the basic principle in which a three-way table lamp operates. On a larger scale this principle is applied to luminaires that contain multiple lamps, in which one or more lamps may be powered at any given time. Bathroom vanities and makeup mirrors often contain lamps wired in several circuits that can provide a limited amount of intensity control. In office buildings, the familiar ceiling fixtures that contain four fluorescent lamps were frequently modified during the energy shortages of the 1980s and ’90s so that only two of the lamps were used during normal conditions while the other two were placed on a separate switch and turned on only when needed. Finally, a room’s lighting can be broken down into several different circuits as opposed to having all of the lights controlled by a single switch. In commercial buildings, this allows the occupants to turn on the lights only in those areas of the room that they are using-once again saving power and lamp life.
