The Model 5.0 UV Meter uses a semiconductor UV sensor consisting of a GaAsP photodiode chip. The Model 5.0 is completely insensitive to visible light longer than 400 nm and infrared radiation since its spectral response covers only the UV region from 260 to 400 nm. Applications include monitoring UV lamp intensity and aging, monitoring PUVA therapy lamp intensity and aging, measuring outdoor UV, testing acrylic shield transmission, eyewear UV block comparison, and testing window film / tint transmission. To operate, press and hold push-button switch on face of unit. Aim sensor window in top panel of meter directly at UV source. Note reading on LCD and record if desired. Battery operation voltage is 9V down to 6.5V. Below 6.5V the LCD numbers will begin to dim, indicating the need for battery replacement. Under typical service load, the battery should last approximately 2 years.