In this project,I will show you how to make a reasonably simple ultraviolet black light with a few UV LEDs, a PVC tube, and some other scraps I found in my workshop. This is a fairly simple project perfect for anyone with an appreciation for science and a little experience with LEDs, no advanced knowledge of electronics necessary!

With an ultraviolet light, you can make a few everyday objects glow (fluoresce), read and write secret messages in invisible ink, or just show off your amazing soldering skills.

Ultraviolet light isn't great for your eyes (or your skin), so use caution when handling ultraviolet light and do not shine the light into your eyes for any extended period of time.

Step 1: Supplies

To build this project, you will probably need:

3-5 UV LEDs - these can be purchased online from most electronics distributors
a 0.5" PVC tube - CPVC and other firm plastic tubes with a 0.5" diameter work just as well
some thick wire - a wire coat hanger might work
some thin wire - to connect the LEDs
a few screws, almost any size works
a switch (optional)

Tools:

a soldering iron and solder - basic experience with soldering is recommended
a drill - you'll need to poke a few holes in the tube to make room for the LEDs
paint (optional)
some glue or tape (also optional)
2-3 AA batteries, I used rechargeable 1.2 volt batteries. the LEDs required 3 of them in order to shine at full brightness

Time:

I completed this project in an afternoon

Step 2: Measure, Plan & Design

This project will use about 10" to a foot of PVC pipe. Each battery is 2" long, and you may need three of them to power the LEDs. (Only 2 are needed if they are 1.5 volts each). To better fit the LEDs and batteries, you'll probably want to measure. Allow at least half an inch at either end of the pipe.

We will be using the bottom section of the tube (opposite the LEDs) as a battery holder, since each AA battery is roughly half an inch in diameter. A screw will be placed at the bottom and some thick wire near the top to make a good electrical connection.

Use a pencil to mark the spaces where the LEDs will be, as well as to mark some holes on each end of the battery holder section of pipe. One hole straight through the bottom, an appropriate size for the screw, and another set of holes across the top (I drilled four individual holes) to thread the thick wire through.

Step 3: Drill Some Holes and Paint

Use a drill bit roughly equivalent or slightly larger than the diameter of the LEDs. For the thick wire, drill a set of smaller holes closer to the diameter of the wire. Finally, drill holes in the bottom for the final screw. The thick wire will act as a positive terminal and the screw will act as the negative terminal.

Step 4: Solder the LEDs Together

Solder the set of 3-5 (I used four) LEDs in parallel, like a ladder. Add a length (a little more than half the length of the pipe) of red wire to the positive side of the LEDs. Add another length (a little more than the total length of the pipe) of blue wire to the negative side. The red will connect to the positive terminal of the batteries (that thick loop of wire) and the blue will connect to the negative terminal (screw). Once you have all the electronics put together, test them and make sure everything works. If it all lights up, we're almost finished!

Step 5: Put It All Together

Carefully slide the LEDs into the tube and through the holes. Remove the screw and insert the batteries, with the positive side facing the LEDs, into the battery holder. Re-attach the screw and wind the exposed end of the blue wire around the screw multiple times to ensure a good connection. Bend an exposed section of the red wire into a hook than can be placed around the thick wire. Once the hook is attached, all LEDs should spring to life! Congrats! You now have your very own handheld black light!

You can now use it as a source of UV light for science experiments or even read and write in invisible ink. Just remember that you shouldn't expose your eyes to ultraviolet light for long periods of time.

Enjoy!

-Matt