The instrument has LCD that can display the value of UVC irradiance. When the lamp's output drops to 70% of original-readings, please replace it. Simply and hold the push-button on the face of the unit. Aim the window in the of the meter directly at the UV source. Note reading on LCD and record if desired. To accurate data, please take several tests at the same distance and averaging. Compact radiometer, Uses UV photosensitive devices, Comes with integrated UVC filter, Has good cutoff characteristics. Adopting high-precision digital display accuracy is stable and accurate. no stray light effect, Probe material, UV glass. Widely used for daily UVCtesting of all types of lamps, Effectively help you choose the best and distance of your own bulb. Response spectrum:220-280nm Measurement: 0-2000uW/cm Measurement accuracy: 1uW/cm Response time:T less than equal 0.5s Measurement error:10% Power consumption:less than equal 0.25W Power supply:2xAA battery(excluded) Color:As Shown Material:plastic Package Contents: 1 * UVC Light Meter Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.