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). The reaction area on the test card shows purple indicating that the bulb contains UVB values.  If the card does not show any color, change the bulb annually or earlier and the card can be used up to 500 times when used in 10-second increments.  When not in use, please put the card in a holder or store it in a dark place.   Specifications: texture of material: Nff-71 UV test card Product category: Other aquatic products Weight: 5g Size: as shown Package Included: UV test card*1