Solar meters are compact, handheld radiometers with simple pushbutton operation and NIST-traceable accuracy. They're proudly made in the USA. The Solar meter Model 9. 4 Standard Blue Light Meter measures the blue light region from 422-499nm. Applications include monitoring blue LED/lamp intensity and aging, monitoring aquarium lamp intensity and aging, monitoring acne lamp intensity and aging, testing eyewear actinic blocking capabilities, measuring outdoor blue light, and measuring photosynthetic action spectrum blue band. To operate your Solar meter, aim the sensor window located on the top panel of the meter directly at a light source. Press and hold the push-button switch on the face of the meter and read the results in mW/cm on the LCD screen. For best results take note of the distance the reading was taken from the light source in order to ensure repeatable results. A 9V battery is included, along with a rugged carrying case and Calibration Certificate.