The Diamonds and Gemstones can glow up to 8 hours in total darkness. **Because this is a natural phenomenon there are many factors that create the glow. The *UV index is the most important. The higher the UV index* above the index standard of 3 the better the afterglow. It’s basically the same as getting a sun tan. The stronger the suns rays the quicker the tan. Typically the further south you go toward the equator the higher the UV index.
* UV Index is a standard for measuring the Ultraviolet Light Value by a numerical value. 0 is no UV light with the value of 3 being just enough to start tanning 8 or 9 is much stronger. The highest value ever recorded was in Cusco Peru with a value of 25.
**In testing the longest emission of afterglow from a Ocular Cut Night Glow Brand Diamond after being removed from strong UV light and placed in TOTAL DARKNESS was 8 hours.