The BLAK-RAY ultraviolet Intensity Meter is a hand-held photovoltaic device used to measure ultraviolet intensity, mainly from hot or cold cathode mercury discharge lamps. Visible light does not register on the meters, only ultraviolet plus some infrared. When infrared is present it can be eliminated from the readings as detailed under “Infrared Sensitivity.” Two models are available; one for measuring long wave and one for measuring short wave ultraviolet. Readings are in microwatts per square centimeter (µW/cm2).

The meter consists of a sensor cell attached to a compact metering unit. The sensor cell can be hand-held or placed directly on a surface for measurements. The sensor cell can be used remotely, while connected to the meter housing by a 4-foot extension cord included.

J-221 meter complies with MIL STD 45662-A found in MIL-6868D (J-221 NSN 6635-488-545). Calibration of meters is traceable to NIST.