Wacool; UVB Sensor card 3 pack. This reusable card cn measure ultaviolet(UV) radiation accufrately in 10 seconds. Hold the card under the UV lamp at the basking site to view intensity of the light emitted(low, moderate or high). Low to moderate readings are sufficinet for most reptiels, UV light decreases as it travels away from the bulb. adjust the location of the basking site or bulb until the reading is in the correct range. the bulb will continue to emitt visible light, bugt the UV leel decreases over time. replace the bulb annually or sooner if the card measure s below low intensity level. Card can be used upto 500 time when ued in 10 second increments.