There are a number of dedicated meters available; however, a wide range of scale is normally required, e.g., a range from 0.1 to 100 microwatts per square centimeter (μW·cm-2).25 Safety readings require the lower range, and efficacy requires a range up to at least 10 mW·cm-2. A common practice is to have two calibrated meters: one in reserve and for reference. The two instruments should be periodically compared. The user should retain the manufacturer’s instructions, including a description of the meter, its safe use, and maintenance and calibration of it. Some healthcare facilities contract with a full, outside maintenance contractor that uses calibrated meters and correctly and safely replaces burned-out lamps. Some users retain a simple, less precise meter for staff to use, but the installer uses a professional meter.