I love LED's and am always looking to use them in new ways. Especially for cool effects. I found a great way to couple a blue LED into 1/4 inch tubing. Then by filling the tubing with fluorescent liquid, a glow tube can be created. It took a little experimentation to get right and ended up being very simple. Here is what you will need:
1. Quarter inch clear Tygon tubing (Lowe's or Home depot carries it)
2. Ultra bright blue LEDs (5mm, clear lens, narrow beam i.e. 12-15 degrees)
3. A small plastic squirt bottle similar to a condiment dispensing bottle
4. a Fluorescent Highlighter (Available at most office supply stores)
Step 1: Preparing the Florescent Dye
The first step is to prepare the dye. Take the back off of the fluorescent highlighter. You can ether pry the ink reservoir out. It is an absorbent cylinder soaked in the dye. My first try at this I pulled it out and used a lot of the dye. I put about a teaspoon into the plastic squeeze bottle. This was way to much. It causes the light to be used quickly and not travel far down the tubing.
What ended up working best and is easiest it to place the end of the highlighter over the mouth of the squeeze bottle and let the water absorb some of the die
Step 2: Filling the Tubing
The key to t his is to fill the tubing with no air bubbles and then to seal it by pressing in the 5mm LED. They fit perfectly into the tubing and act like corks. They are actually quite hard to remove if you realize you have air bubble later.
1. Have your LED's standing by so you can grab one quickly
2. Hold the tubing so that the ends are even
3. Hold the nozzle of the squeeze bottle next to one end of the tubing
4. Squeeze the bottle so as to have the liquid flow out the other end of the tubing
5. Pull the bottle away and stop squeezing. If you stop squeezing first, the bottle sucks liquid back out of the tube.
6. Push an LED into one end of the tube to seal it.
Step 3: Sealing the Tubing
Now we have to get the next LED into the tubing without air bubbles. Do this by dripping a few extra drops of liquid into the open end until it is completely full. Now press the second LED into the tube to seal it.
Step 4: Testing
For testing purposes I used a CR2032 battery just like an LED "Throwie" uses. It is perfect to test and depending on your final use can power the LED Glow tube for costumes etc. You can get these pretty cheap from Dealextreme: http://www.dealextreme.com/details.dx/sku.751
Step 5: Use and Final Thoughts
These are not quite as bright as a glow stick in the first few minutes. They are brighter than the glow necklaces that are sold at a lot of events. What is really cool is that you get the green glow and some blue leaks through also. The glow definitely drops off further away form the LED but by lighting both ends it makes up for it. The other cool thing for me is that it looks different than EL wires and chemical glow sticks. Begging the question of just what is it?
Interestingly, I started out with UV leds and found that they do work but are not as effective at florescence es as the the blue LED's. Mine are 470nm and my UV ones were 405um. Also the minimal amount of die needed was a surprise. I tried an orange and pink fluorescent highlighters too but they were no where near as bright.
I am wiring mine up with 330Ohm resistors so I can power them from 12 volts for a couple Halloween projects. They can be directly connected to the little CR2032 batteries and will last for a couple days, although at reduced brightness.
What projects can you put these into?