The center of the Solar UV Meter with 3D effect can change series of color according to Solar UV Index. It is how Solar UV measuring function is maintained. The 4 standard color indicators show intensity of Solar UV rays. To know the Solar UV Index, it is enough to compare the color change with the 4 standard colors around. The greater intensity is the darker is the color.
Clear colors mean small intensity and dark colors mean great intensity of Solar UV rays.
Very light purple: low intensity, UV index 1-2. Sun-protection not necessary.
Light purple: medium intensity, UV index 3-5. Sun-protection is recommended.
Purple: strong intensity, UV index 6-7. Sun-protection is necessary.
Dark purple: very strong intensity, UV index 8-11. Avoid exposure. Circle-shaped UV tester with keychain is convenient to use.