UV index is a measure that indicates how much Ultraviolet radiation which is UV in sunlight or light from the lamp reaches a certain spot.
This is expressed in figures 1 is very low and 11 is extremely high for humans then.

How is the UV light test card in use? Very simple!

Keep the card 10 seconds under your lamp
Get him out from under the lamp and look at the color that best matches
UV decreases as you move away from the lamp goes off. This makes it easy to measure where the animal is normally

Measurements are highly accurate, but would like to know the exact output of your UV lamp? then choose a UV meter.
This is because the UV lamp testing cards also at higher radiation (UVI of 10 or higher) responds to UVA and UV meters are not susceptible.

UV or UV index is a measure for the amount of ultraviolet radiation (UV) is in the light.
The RepTech UV card measures these UVI radiation and converts it into a color of which is to read what is the index of the lamp.