UV torch with 9 L.E.Ds .
Read all about how UV light works; see lots of photographs of what you will see with UV light, click here.
Note: this is a UV (ultra violet) lights, for ordinary (white light) lights click here.
Wavelength: probably about 400nm
Size: 3.5 inches long X 1 inch diameter (90 X 25mm)
Power: three AAA batteries
More info, more pictures
Click on the picture above, see the security markings on an old (pre-2017) twenty pound note,