The instrument has an LCD that can display the value of UVC irradiance. When the lamp's output drops to 70% of original readings please replace it. Simply press and hold the push-button on the face of the unit. Aim the window in the of the meter directly at the source. Note reading on LCD and record if desired. To get more accurate data, please take several tests at the same distance and averaging. Compact , Uses imported photosensitive devices, Comes with an integrated UVC filter, Has good cutoff characteristics. Adopting high-precision digital , display accuracy is stable and accurate. Imported , light effect, Probe , glass. Widely used for daily UVCtesting of all types of lamps, Effectively help you choose the best and distance of your own bulb.