This reusable card can accurately measure UV radiation in 10 seconds. Check that the lamp is in use by placing the card on the spot under the UV lamp (within 5cm from the lamp). Easy for you to use. When the reaction area on the test card shows purple, indicating that the bulb contains UVB values.If the card does not show any color, otherwise change the bulb. And the card can be used up to 500 times when used in 10-second increments. It is constructed of plastic material. The length of this product is 8.6cm and width is 5.4cm. When not in use, please put the card in a holder or store it in a dark place. Suitable for reptile terrarium tank, feeding box, daily fluorescent lamp, etc. Item Name: UV Sensor Card Material: Plastic Usage: UV Rays Test Features: Reusable, Quick Test, Quick Test Size Details: L: 8.6cm or 3.39", W: 5.4cm or 2.13"(Approx.) Notes: Due to the light and screen setting difference, the item's color may be slightly different from the pictures. Please allow slight dimension difference due to different manual measurement. Package Includes: 1 x UV Sensor Card Note: Due to the light and screen setting difference, the item's color may be slightly different from the pictures. Please allow slight dimension difference due to different manual measurement.