Monday, July 2, 2012

DIY Glow In The Dark Fob

After some experimentation with Glow-in-the-Dark pigment powder and creating the "fireworm", I came up with an application for it - an inexpensive but IMHO pretty cool solution for a GITD fob. This fob can be attached to any object, one might look for (or want to avoid) in the dark - flashlights, , keychains, backpacks, zipper pulls, water bottles, weapons, light switches (regular or pull-chain), cabinet handles, hand-held radios, etc - the list is endless. It is nothing fancy, but it is inexpressive, easy to make and very durable.
The bill of materials includes:
1. Fine particles Glow In The Dark powder - Europium activated Strontium Aluminate (green color is the brightest, followed by ice-blue in glow intensity). There are number of Internet sites selling it (,, etc).
Strontium Aluminate is the "good stuff" - it is VASTLY better than the old zinc sulfide pigment and after it is fully charged, it will glow for as many as 8 to 12 hours. (very bright for the first couple of hours and of course, 8 hr. later it will be dim but still visible in complete darkness). For comparison, the Zinc Sulfide GITD pigment will not be visible an hour after charge. Charging time, light intensity and spectrum are the main factors when it comes to glow duration.
GITD pigments work very much like a rechargeable "light battery" going thorough charging-discharging cycles. Light (UV emissions in particular - 200-450 nm wavelength) raises the electrons from a baseline energy level to an excited level. When the exciting radiation is gone, the electrons try to go back to their baseline energy level but get trapped in a "meta-stable" level from which they go to their baseline level after some delay.
The energy which excited them in first place is stored in the meta-stable level and then released when the electrons make the transition to their baseline energy level. This energy release is in the form of photon emission (light))
When purchasing, make sure that the pigment is manufactured as fine particles - not large particles which are then crushed, as breaking the crystals will change the glow properties.
2. Clear Vinyl Tubing - I used 1/4" OD but other sizes will work too. (hardware or home improvement stores). It must be tested beforehand for UV protection agents as I encountered tubing which contains such. (This cab be done easily by placing some of the GITD powder inside the tubing and exposing it to light)
3. Clear, LOW-ODOR Silicone sealant. Low-odor type is not very (or at all) acidic. Normally, as the silicone sealant cures, it releases acetic acid which might react with the pigment (again hardware/home improvement stores). I used the "Kitchen/bath" sealant as it is less likely to contain UV block agent but this is speculation on my part - I need to do some tests to confirm if such agent is present.
4. Small size cable tie
5. Strong, thick, braided type nylon string.

In addition, a small, shallow, colored plastic container, plastic spatula or flat tip screwdriver and a large syringe ( I got one from a pet supply store) are needed.

I mixed a few milliliters of silicone sealant with some of the glow powder. One must work quickly as the silicone will start curing once it is out of the container. I worked under a bright light, turning it off a few times, while adjusting the ratio of the mixture. The goal is to get as much glow powder as you can while still preserving some of the transparency of the mixture in a "test dab" approx 4-5 mm thick (hence the colored plastic mixing container). The idea behind this is to allow the light to "soak through" and charge the entire "glow core" of the tubing, even if it only comes from one direction. If the mixture is too "loaded" with glow powder it will become opaque and only the side, exposed to light during charging will glow (it will become also too thick to inject and not as flexible when it cures). Use plastic spatula to mix it very well (for a uniform glow) and load the mixture through the back of the syringe. I cut the vinyl tubing into 2 1/2" - 3" pieces and injected the mixture in each piece. While injecting, I stop when the mixture reaches about 1/2" from the opposite end of the tubing. Air bubbles can be avoided by first squeezing the air out of the syringe and also injecting in one smooth, continuous motion of the plunger.
It takes a couple of days for the silicone to completely cure as it is inside an almost sealed space. After that, the lower end of the tubing (where the injection was done) can be trimmed.
I made a small loop from the string with a double knot at the end. (If the string is thin, keep adding to the knot until it barely fits inside the tubing). I pushed the knot into the empty 1/2 inch portion of tubing and used a cable tie to squeeze the tubing right above the knot, trapping it. As an alternative, large-diameter wire-splice copper ferule can sliced to 3-4 mm rings and crimped - it might look better but I like the all-plastic version.

That's all! In an hour, I made over a dozen of these in green and ice-blue colors to mark different objects and devices. I like both colors but the ice-blue reminds me of Cherenkov radiation :-)
One neat thing is that because of the optical refraction properties of the 1/4" clear vinyl tubing, once filled with the glow mixture, the tubing walls are not visible anymore from the side - it appears as if the tubing wall is paper thin and the entire thing glows. In other words - the tubing wall acts as a lens, magnifying the GITD core.
I am not one these ARES freaks (on contrary - I have very little love for ARES) so I don't have an ARES go-box full of gear or the ridiculously tacky cooler turned into portable station (don't even want to discuss the ply wood versions) but these GITD fobs come pretty handy during power outages or camping.

The cool thing is that such GITD fob is VERY durable and can take a lot of abuse - it is 100% weather-resistant, soft and flexible, it will not break or tear easily and can be used for many many years. Most importantly for me - it is made entirely out of soft plastics and will not scratch the surface of  the object, which it is attached to. (metal fobs can scratch the anodizing finish of a flash light or damage powder coating, plastic surfaces like the display bezel of a HT radio and acrylic fobs get scratched themselves by metal parts)
Longer pieces can be even sewn to clothing - hats, jackets, shoes, gloves as a "tracer" and will not be affected by regular washing.
This GITD fob works best when used outdoors as it needs about 10-15 min direct sun light to fully charge (or a couple of minutes with a high-power flashlight will do the job too) - the longer, the better. In artificial lighting environment, it works better when charged with fluorescent, LED or halogen lights than the regular incandescent type.
If the object is normally always in the dark (in a box, pouch, cabinet) it is useless to have one of these - try tritium vials.

(Tip: For a neat GITD electric light switch face-plates, I used smaller OD tubing. Two holes (the size is the of the tubing) are drilled in the face-plate - approx. 3/4" apart and connected using a small file. This creates a small, elongated window. A slightly longer piece of the glow tubing is then attached on the back side with hot-melt glue.)


Unknown said...

good day

where could i buy the GITD powder i'm from South Africa and don't know where to get it.
please help

best regards

Andrey E. Stoev said...

Just try eBay. Search for "glow in the dark powder" and then check the sellers for their shipping options. There are many who ship internationally and will ship to South Africa