In order to see within closed objects devoid of ambient light, light is provided to the VE by a cold (low-heat-producing) light source. A fiber-optic light guide connects the light source with the VE. Light can then travel through the fiber optics of the VE insertion tube and illuminate the field of view at the distal tip. Light sources vary in their configuration and should be matched to the application at hand (Figure 4.15). For example, in field applications, compactness, portability, and battery operational capabilities are the major considerations. Light sources are available that weigh approximately
4 lb, about the size of a hair dryer, and can be operated by battery. Other portable light sources are handheld, like a flashlight. These basic light sources are simple in their operational aspects as well with an on/off control and a brightness control. The light is typically derived from a halogen bulb. Portable light sources may also use LED lights for illumination. If the endoscopic application is to be conducted in a laboratory setting, additional light source options become available. Higher-wattage light is available as well as additional controls such as filters, exposure indexing, and air pumps.
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