Intro: Creepy UV LED Sun Jar!
I'm the kind of instructabler who makes a lot of sun jars, as well as othersolar powered LED devices. I've built several of these with UV LEDs in them, as I like the weird purplish glow, but they're very dim. Now with the simple addition of some glow in the dark paint, the full power of the UV LED is revealed!
As with all of my instructables, if you make your own version of this, be sure to post a picture in the comments and I'll send you a digital patch!
Step 1: SCIENCE!
If you're not interested in how this works, feel free to skip to the next step. Stick around if you're awesome and want to learn about ultraviolet radiation, the visible electromagnetic spectrum, and fluorescence.
Human beings can see in a very narrow band of the electromagnetic spectrum, about 750nm (red) to 390nm (violet)--do you remember ROY G. BIV from gradeschool science class? This is just a tiny chunk of the spectrum, which ranges from radio waves (longest wavelength) at the very bottom all the way up to gamma rays (shortest wavelength) at the very top. Just below the human visible sprectrum is infrared light, far infrared being heat and near infrared is what people use for active nightvision and remote controls. Here we're more concerned with the other end of the spectrum, ultraviolet light. This is the stuff that gives you a tan (or skin cancer) if you get too much of it, though we're working with very safe levels so don't panic.
An ultraviolet LED will put out most of it's light in the invisible near UV range, with it's major output around 375 nm, just outside of our range, but with a smaller output around 400 nm, or just within range. For this reason, to the naked eye an UV LED or a blacklight looks pretty dim, but really they're pumping out quite a bit of light that you can't see. Here's a chart from wikipedia to clarify.
So what good is a bright light that looks dim? Well, UV light has an interesting property, in that it causes a number of chemicals to fluoresce. Fluorescence is when a chemical absorbs light of one spectrum and emits light of a lower spectrum. In this specific case, the high energy UV photon strikes some glow in the dark paint, causing it to emit a spooky green glow (around 540nm, at a guess). Thus, spooky sun jar!
Step 2: Gather Supplies
- Solar Garden Light
- Wire Bale Glass Jar
- Glow-in-the-dark Paint
- UV LED (I get mine from dealextreme)
- Aluminum Foil
As to tools, you'll need:
- Wire Cutters
- Soldering Iron
- Sturdy Scissors
- Screwdriver (maybe)
- Stirring stick
- Hot Glue Gun
I got very lucky, as I happened by the dollar store this summer when they had solar garden lights. I bought a couple dozen, figuring that they'd probably be crap but I could at least reuse the parts for other projects. Much to my surprise, they were actually quite good quality! I went back the next day to buy their complete stock, and I guess someone beat me to it! So anyway, I started checking back whenever I thought about it, and while I never got any more solar lights, they did get a big shipment of wire bail glass jars, which I promptly bought 40 or 50 of!
Step 3: Paint the Jar
Stir the paint thoroughly. Make sure to scrape the bottom, a lot of the glowy stuff settles down there and hardens even with the lid closed. You can still break it up and stir it back in though.
I used a brush like the one you see in the pictures below, I think it worked a lot better than a standard paintbrush would have. I applied a coat, hit it with the hairdryer, and repeated, for three coats total. Don't leave much settled at the bottom, it won't do any good down there.
Step 4: Prep the Electronics
If you've made these before, this will seem like old hat, but if this is your first sun jar, read on.
First you'll need to dismantle the solar garden light. Just keep in mind, you only need three things: the battery and holder, the circuit board, and the solar panel. Just make sure these are intact and all the connections are good, everything else can be cut away and discarded, or saved for future projects (that's what I do!).
It's a lot easier to get clear LEDs than diffused, so just get the clear ones. Using a piece of sandpaper, scuff up the outside of the LED. Instant diffusion!
With that done, snip the connections of the LED that came installed in the solar light. Keep track of which side is positive and which is negative. This is easy if they've marked it on the circuit board, but if not pay attention to the LED itself--they're almost always flat on the negative side. Solder on the new UV LED in its place, making sure to get a good solid join.
Step 5: Install the Electronics
I've had a lot of practice making these, and I find that this is the best way to assemble them:
- Hot glue two corners of the panel to the lid
- Let it cool
- Hot glue the battery holder to the panel
- Let that cool
- Hot glue the circuit board to the battery holder
- Let it all cool for a few minutes
- Epoxy everything thoroughly--E6000 has worked best for me
Let the paint and the epoxy dry overnight before moving on to the next step.
Step 6: Install a Reflector
I do this to most of my sun jars, as much of the light is focused on the bottom of the jar where it won't do any good.
Get a piece of foil, fold it up until it's about the size and shape of the bottom of the jar, then press it into place. This reflects a lot more light back up to the glow in the dark paint and makes it much brighter than it would be.
Close everything up and put it outside in the sun, you're done!
Step 7: Final Thoughts
Thanks for viewing my instructable, I hope you liked it! If you did, please take a moment to rate, subscribe, and comment! Do you have any questions or recommendations? Did I leave anything out?
As with all my instructables, if you make your own version of this, be sure to post a picture in the comments and I'll send you a digital patch!
Thanks for stopping by!
Finalist in the