The Jetbeam Jet UV is built on their Jet Mu singe AAA cell light design. This is a solidly built light with Twist-On/Off operation, so there is no inadvertent actuation or standby battery drain. The threads are well cut and lubed; twist is smooth. When twisted perhaps 10 degrees to off, the light can be easily actuated momentarily by simply pressing with the thumb against the head of the light, pushing it toward the supporting forefinger. With output at 365nm it provides an effective UV spectral output for the various UV light tasks... since that's so, beware of where you shine or reflect the beam (pro UV lights often ship with UV protective "sunglasses"). Fortunately, the LED used gives output spilling into the visible range (400nm and up) so there is visible bright purple-white output, unlike infrared lights, or other UV lights whose LED's output is completely or almost completely invisible.
I tested this light using currency from the US, Hong Kong, Thailand, Siri Lanka, and India with very good results compared to Inova's UV microlight and Coast UV pocket light, whose output appears both weaker and more to the 385nm wavelength, which means fluorescing colors are not as accurate or bright as with the Jetbeam Jet UV.
The Battery Junction Jetbeam Jet UV description covers the various uses of a UV light. What you need to know is that this is far better in build and function than most UV microlights, so it's just the ticket for those who need a durable, reliable, every-day-in-use UV light for checking currency, security markings, and other fluorescence as part of their job. It's one of a very few UV lights that even specify output in terms of wavelength, output power, and run time. Comes with a split ring, pocket clip, quality wrist lanyard, and extra O-ring.
Regular users likely best served with an NiMH rechargeable AAA cell; for in-the-drawer-if-I-need-it use, choose a Lithium Iron primary AAA cell for leakproof, long term shelf and standby operation.

The Jetbeam JET UV Light is built on the JET Mu body with a different pill and driver, and offered in Red and Blue Anodizing. Looks good, works good. Small yet solid build by Jetbeam, making a durable, dependable light with dependable Twist On/Off operation using a single AAA cell. UV "color" is in a good range for the tasks one uses this for. Here is a durable, reliable, drop-in-pocket or clipped-to-shirt-pocket solution for such needs. For frequent use during the day, use an NiMH rechargeable cell; for stashing in your desk drawer for some rare future use, better to use a Lithium Iron primary cell so there's no damaging cell leakage as you'd experience with an Alkaline over time.

This key chain light provides a good amount of UV light for viewing larger items up close. The only reason for 3 stars is that I purchased another similar light of a different brand which is 25% cheaper and more powerful and smaller yet.

A good value. Not the top of the line but priced accordingly.

I bought some invisible ink for my fountain pen and this light is fantastic for viewing!