This instructable will illustrate how to make a hand held black light. This black light was almost free and has withstood a five year old and dozens of scorpion hunts.
Step 1: Tools
1) Soldering Iron (solder, flux)
2) Hot Glue Gun
3) Wire strippers (or sharp finger nails)
Step 2: Materials
Step 3: Assemble LED's
I had a small round PCB board with UV LEDs and correctly sized SMD (Surface Mounted Device) resistors pre-assembled. Otherwise you can easily calculate the required resistance for your LED's and battery setup. Here are two calculators that you can simply input your setup parameters and calculate automatically the resistance required. If using more than one UV LED wire them in series with the resistor and add the Diode forward voltage of the LED's for the calculation (The second more detailed calculator will make the calculation for you).
Note that NOT using a resistor will quickly burn them out as LED's will take as much current as can be supplied by the source. Since the source can usually always supply more current than the LED can handle they burn out.
Step 4: Switch and Battery Case
Solder the switch between the batteries and LED's. I chose a push button switch to prevent my kids from leaving the light on as this switch requires constant pressure to stay on. Positioning of the switch is not important as long as it breaks the circuit.
Step 5: Finalize
Hot glue everything together, the younger the user the more hot glue you should apply.
Put in batteries, test and find scorpions.