This tiny flashlight is super easy to make and only costs about $10 in parts!
Step 1: The Parts
First, you will need a project box big enough to hold all the components. You can purchase these at RadioShack; I purchased mine online. An altoids tin would also work. Whatever works for you aesthetically.
You will also need: two super bright 5mm leds (I'll be using 15,000 mcd white), 2 led mounts, 2 CR2016 batteries, a coin battery holder, and some wire.
Not pictured: You will need a switch to turn the light on and off. You can choose a toggle switch, slide switch, or a push button. Again, this is largely a question of aesthetics. You should consider though if a momentary switch or an off/on type would best suite your needs. I chose an oversized push button that does both.
Step 2: Assembly
Start by drilling two holes in the box for the led mounts and then attach them. A 5/16 drill bit should be the perfect size.
(Make sure you don't put the mounts too close together or you wont be able to screw on the nuts.)
After the led mounts are done, you can Insert the two leds.
Next, drill a hole for the switch and attach it.
Step 3: Soldering
Now you are ready to solder! The leds should both have a long wire (the cathode) and a short wire (the anode). Solder one of the led's anode wire to the other led's cathode wire.
Next, solder one of the led's remaining wires to one side of your switch.
Then solder a small piece of wire to the other side of the switch.
Finally, solder that piece of wire to one of the tabs on the battery holder. Solder the other tab to the unused led wire. (Keep in mind that you have to have the battery holder wired for the correct polarity. It helps to test this before you solder, though if you mess up you can always just flip the batteries upside down.)
Step 4: Final Touches
Insert the batteries and test it out. If everything works then you're almost ready to close it up. Before you do though, it's a good idea to cover the solder joints and bare wires with liquid electrical tape to avoid shorts.
Now you have a very cool pocket light to show off to your friends!
A few final thoughts:
This design leaves a lot of room for modification. You could try different colour leds, more/less leds, you could add a potentiometer to make it a variable light, ect. You could also add another battery (the holder will fit multiple fairly well) to make the light noticeably brighter, but you would need to add a couple of resisters or your led life would probably be shortened. Have fun experimenting.