The instrument has an LCD that can display the value of irradiance. When the 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 UV 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 radiometer, Uses imported UV photosensitive devices, Comes with an integrated filter, Has good cutoff characteristics. Adopting high-precision digital AD, display accuracy is stable and accurate. Imported no stray light effect, Probe material, UV s. Widely used for daily testing of all types of lamps, Effectively help you choose the best and distance of your own bulb.