This flashlight works great with this "invisible" ink UV reactive marker.You can write secret messages that can only be seen in UV light.Just some of the uses for UV LED lights: - Bugs/Insect Detection - Minerals Hunting - Police use it for scanning the crime scene Unbreakable - Checking currency and ID - Fluorescent inks/dyes used as anti-counterfeiting measures - Examining artwork and glasswork for hidden repairs - Locating damaged/cracked glassware - Detecting scorpions Specifications: Bulb Life :100,000 Hours Battery Life :Approximately 40 hours on 3 AAA batteries (not included) Switch Type :Press on, Press off from rear cap Weight :2 oz.Head Diameter:1.2" 31 mm Body Diameter :1.08" or 27.5 mm Length : 3.8" or 94.2 mm