A true woods lamp is UV and emits at 385-400nm. I use flourescein to stain for corneal pathology and the optimal excitable wavelength is 450-500nm so this conversion was perfect because the LEDs I had were 485-500nm.
When you get down to it, this was just another great reason to hack something.....
Step 1: Materials
Here's what I used for this conversion:
1.) pocket LED magnifier - got this one on sale at Office Depot
2.) Blue LED - took mine from a piece of blue LED reel I use on my multirotors
3.) soldering iron
4.) thin flathead screw driver
5.) desoldering copper braid
6.) heat gun
7.) gorilla glue (super glue works fine)
Step 2: Dismantle Magnifier
Use a thin flathead screw driver to pry the halves apart. After removing the batteries, start the separation at the battery compartment. As the halves begin to separate, work your way around the magnifier until you've completely separated the pieces.
Step 3: Remove Old LED
The LED is small so be careful not to damage the surrounding structures. I used braided copper to facilitate the removal of the solder on the LED pads.
Once the pads are clear, remove the old LED.
Step 4: Prepare New LED
Remove the waterproof plastic from the top. Separate out a single LED. We need to access the tiny + and - pads without damaging the unit.
The best way to remove the sticky backing is to use a heat gun. Place the led over the heat gun and after about 30 seconds you can easily strip away the backing exposing the metal contacts.
Step 5: Solder LED
Place the new LED on the tinned pads making sure you have the correct polarity.
Carefully solder the LED into place. Make sure it's well seated to ensure proper closure of the 2 halves.
Step 6: Put Magnifier of Awesomeness Back Together!
Although you don't have to glue them together, I highly recommend it. I'm a fan of gorilla glue so after the clamps came off it wasn't coming apart!