Experiment 18: UV Battery Attachment

While gathering sample IC chips for my Raspberry Pi laser cutter project (which is now on hold until I find some proper stepper motors - I searched two printers, but to no avail), I came across some really awesome ultraviolet (UV) LEDs.  They were free samples, so naturally, I ordered some.  After seeing this Instructable, I decided to replicate it with my LEDs.  The idea is to connect two UV LEDs and a resistor to a 9V battery clip, in order to make an ultraviolet battery attachment that turns your battery into a flashlight of the most amazing (and ghoulish) purple color.  I used this online electrical calculator to figure out the right resistor value for the LEDs.  A resistor is absolutely necessary because without one, your LEDs will be fried by the 9V battery.  For my two 3.4V 15mA LEDs and a 9V battery, the calculator told me to use a 150 ohm resistor.  I didn't have one, so I used two ~87 ohm resistors, for a total value of ~174 ohms, which is close enough.  Then, I bent the leads of the LEDs and soldered them and the two resistors to a 9V battery clip, obtained from Experiment 5: 9V Battery Clips.  Thus, I had a battery clip flashlight that would easily attach to any 9V battery.  I tried it and it worked great!  The LEDs, as stated above, shine with an intense, ghoulish purple color that looks absolutely amazing!  Here is a better-quality picture of the flashlight, in daylight: